ASTM C518-21

Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus

SIGNIFICANCE AND USE
4.1 This test method provides a rapid means of determining the steady-state thermal transmission properties of thermal insulations and other materials with a high level of accuracy when the apparatus has been calibrated appropriately.  
4.2 Proper calibration of the heat flow meter apparatus requires that it be calibrated using specimen(s) having thermal transmission properties determined previously by Test Methods C177, or C1114.
Note 1: Calibration of the apparatus typically requires specimens that are similar to the types of materials, thermal conductances, thicknesses, mean temperatures, and temperature gradients as expected for the test specimens.  
4.3 The thermal transmission properties of specimens of a given material or product may vary due to variability of the composition of the material; be affected by moisture or other conditions; change with time; change with mean temperature and temperature difference; and depend upon the prior thermal history. It must be recognized, therefore, that the selection of typical values of thermal transmission properties representative of a material in a particular application should be based on a consideration of these factors and will not apply necessarily without modification to all service conditions.  
4.3.1 As an example, this test method provides that the thermal properties shall be obtained on specimens that do not contain any free moisture although in service such conditions may not be realized. Even more basic is the dependence of the thermal properties on variables, such as mean temperature and temperature difference. These dependencies should be measured or the test made at conditions typical of use.  
4.4 Special care shall be taken in the measurement procedure for specimens exhibiting appreciable inhomogeneities, anisotropies, rigidity, or especially high or low resistance to heat flow (see Practice C1045). The use of a heat flow meter apparatus when there are thermal bridges present in the specimen may ...
SCOPE
1.1 This test method covers the measurement of steady state thermal transmission through flat slab specimens using a heat flow meter apparatus.  
1.2 The heat flow meter apparatus is used widely because it is relatively simple in concept, rapid, and applicable to a wide range of test specimens. The precision and bias of the heat flow meter apparatus can be excellent provided calibration is carried out within the range of heat flows expected. This means calibration shall be carried out with similar types of materials, of similar thermal conductances, at similar thicknesses, mean temperatures, and temperature gradients, as expected for the test specimens.  
1.3 This a comparative, or secondary, method of measurement since specimens of known thermal transmission properties shall be used to calibrate the apparatus. Properties of the calibration specimens must be traceable to an absolute measurement method. The calibration specimens should be obtained from a recognized national standards laboratory.  
1.4 The heat flow meter apparatus establishes steady state one-dimensional heat flux through a test specimen between two parallel plates at constant but different temperatures. By appropriate calibration of the heat flux transducer(s) with calibration standards and by measurement of the plate temperatures and plate separation. Fourier’s law of heat conduction is used to calculate thermal conductivity, and thermal resistivity or thermal resistance and thermal conductance.  
1.5 This test method shall be used in conjunction with Practice C1045. Many advances have been made in thermal technology, both in measurement techniques and in improved understanding of the principles of heat flow through materials. These advances have prompted revisions in the conceptual approaches to the measurement of the thermal transmission properties (1-4).2 All users of this test method should be aware of these concepts.  
1.6 This test method is ...

General Information

• Status: Published
• Publication Date: 31-Aug-2021
• ICS: 91.120.10 - Thermal insulation of buildings
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.30 - Thermal Measurement

Relations

• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM E230/E230M-23a - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-Nov-2023
• Refers: ASTM E230/E230M-23 - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-May-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM C1045-19 - Standard Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
• Effective Date: 01-Apr-2019
• Refers: ASTM C1114-06(2019) - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
• Effective Date: 01-Mar-2019
• Refers: ASTM C687-18 - Standard Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
• Effective Date: 01-Sep-2018
• Refers: ASTM C168-18 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2018
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM C168-17 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2017
• Refers: ASTM C687-17 - Standard Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
• Effective Date: 15-Mar-2017
• Refers: ASTM E178-16 - Standard Practice for Dealing With Outlying Observations
• Effective Date: 01-Jun-2016
• Refers: ASTM C168-15a - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Oct-2015
• Refers: ASTM C167-15 - Standard Test Methods for Thickness and Density of Blanket or Batt Thermal Insulations
• Effective Date: 01-Sep-2015

Overview

ASTM C518-21, titled "Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus," is an internationally recognized standard published by ASTM International. This standard specifies the procedures for determining the steady-state thermal transmission properties-such as thermal conductivity, thermal resistance, and thermal conductance-of flat slab materials using the heat flow meter (HFM) apparatus. Widely employed in thermal insulation testing, this method offers a rapid, accurate, and efficient approach, provided that the equipment is properly calibrated. ASTM C518-21 supports quality control, product certification, and material characterization in industries where understanding thermal performance is essential.

Key Topics

• Purpose and Scope: Defines a method to measure steady-state thermal transmission in flat specimens using a heat flow meter. Applicable to a wide variety of insulation materials and other materials.
• Calibration Requirements: Emphasizes the importance of calibrating the heat flow meter apparatus with reference specimens whose thermal properties are traceable to standards determined by absolute measurement methods (such as ASTM C177 or C1114).
• Test Conditions: Specifies the need for matching the calibration and test conditions (such as mean temperature, temperature difference, material type, and thickness) to achieve precise and reliable results.
• Factors Affecting Measurements: Recognizes variability due to material composition, moisture content, mean temperature, temperature gradient, and prior thermal history. It is important to note that values measured may not represent all service conditions.
• Apparatus Design: Details necessary features of the heat flow meter apparatus, including isothermal plates, heat flux transducers, and measures to reduce edge heat losses (e.g., edge insulation or guard heaters).
• Result Reporting: Outlines reporting criteria to document test conditions, calibration details, measurement uncertainty, and physical properties of the specimen.

Applications

The ASTM C518-21 test method is widely used in:

• Thermal Insulation Testing: Determining the thermal conductivity and resistance of insulation products such as fiberglass, foam boards, loose-fill, blanket, and batt-type materials.
• Building Materials Evaluation: Assessing wallboard, roofing, flooring, and other flat building materials for energy efficiency purposes.
• Product Certification and Quality Control: Supporting manufacturers and laboratories in certifying insulation materials and maintaining compliance with building codes and regulations.
• Research and Development: Facilitating the development, comparison, and optimization of new thermal insulation products and materials for residential, commercial, and industrial applications.
• Material Characterization: Generating reliable thermal transmission property data for use in thermal design calculations, product literature, and regulatory submissions.

Related Standards

ASTM C518-21 references or is closely related to the following standards:

• ASTM C177: Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus (primary or absolute method of calibration).
• ASTM C1114: Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus.
• ASTM C1045: Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions (used in conjunction with C518).
• ASTM C167, C687: Related to thickness, density, and preparation of insulation specimens.
• ISO 8301:1991: Thermal insulation-Determination of steady-state thermal resistance and related properties-Heat Flow Meter Apparatus (the international equivalent to ASTM C518).
• ASTM C1058, C1046: Provide guidance on temperature selection and in-situ heat flux measurement.

By following ASTM C518-21, laboratories and manufacturers ensure standardized, consistent, and accurate measurement of thermal properties, supporting the effective specification, selection, and certification of insulating and thermal materials across industries.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C518 − 21
Standard Test Method for
Steady-State Thermal Transmission Properties by Means of
the Heat Flow Meter Apparatus
This standard is issued under the fixed designation C518; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope approaches to the measurement of the thermal transmission
properties (1-4). All users of this test method should be aware
1.1 This test method covers the measurement of steady state
of these concepts.
thermal transmission through flat slab specimens using a heat
1.6 This test method is applicable to the measurement of
flow meter apparatus.
thermal transmission through a wide range of specimen prop-
1.2 The heat flow meter apparatus is used widely because it
ertiesandenvironmentalconditions.Themethodhasbeenused
is relatively simple in concept, rapid, and applicable to a wide
at ambient conditions of 10 to 40°C with thicknesses up to
rangeoftestspecimens.Theprecisionandbiasoftheheatflow
approximately 250 mm, and with plate temperatures from
meterapparatuscanbeexcellentprovidedcalibrationiscarried
–195°C to 540°C at 25-mm thickness (5, 6).
out within the range of heat flows expected. This means
1.7 This test method may be used to characterize material
calibration shall be carried out with similar types of materials,
properties, which may or may not be representative of actual
of similar thermal conductances, at similar thicknesses, mean
conditions of use. Other test methods, such as Test Methods
temperatures, and temperature gradients, as expected for the
C236 or C976 should be used if needed.
test specimens.
1.8 Tomeettherequirementsofthistestmethodthethermal
1.3 This a comparative, or secondary, method of measure-
resistance of the test specimen shall be greater than 0.10
ment since specimens of known thermal transmission proper-
m ·K/W in the direction of the heat flow and edge heat losses
ties shall be used to calibrate the apparatus. Properties of the
shall be controlled, using edge insulation, or a guard heater, or
calibration specimens must be traceable to an absolute mea-
both.
surement method. The calibration specimens should be ob-
tained from a recognized national standards laboratory. 1.9 It is not practical in a test method of this type to try to
establish details of construction and procedures to cover all
1.4 The heat flow meter apparatus establishes steady state
contingencies that might offer difficulties to a person without
one-dimensionalheatfluxthroughatestspecimenbetweentwo
pertinent technical knowledge. Thus users of this test method
parallel plates at constant but different temperatures. By
shall have sufficient knowledge to satisfactorily fulfill their
appropriate calibration of the heat flux transducer(s) with
needs. For example, knowledge of heat transfer principles, low
calibrationstandardsandbymeasurementoftheplatetempera-
level electrical measurements, and general test procedures is
tures and plate separation. Fourier’s law of heat conduction is
required.
used to calculate thermal conductivity, and thermal resistivity
1.10 The user of this method must be familiar with and
or thermal resistance and thermal conductance.
understand the Annex. The Annex is critically important in
1.5 This test method shall be used in conjunction with
addressing equipment design and error analysis.
Practice C1045. Many advances have been made in thermal
1.11 Standardization of this test method is not intended to
technology, both in measurement techniques and in improved
restrict in any way the future development of improved or new
understanding of the principles of heat flow through materials.
methods or procedures by research workers.
These advances have prompted revisions in the conceptual
1.12 Since the design of a heat flow meter apparatus is not
a simple matter, a procedure for proving the performance of an
apparatus is given in Appendix X3.
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved Sept. 1, 2021. Published September 2021. Originally
approved in 1963. Last previous edition approved in 2017 as C518 – 17. DOI: The boldface numbers in parentheses refer to the list of references at the end of
10.1520/C0518-21. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C518 − 21
1.13 The values stated in SI units are to be regarded as 3. Terminology
standard. No other units of measurement are included in this
3.1 Definitions—For definitions of terms and symbols used
standard.
in this test method, refer to Terminology C168 and to the
1.14 This standard does not purport to address all of the
following subsections.
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.2.1 calibration, n—the process of establishing the calibra-
priate safety, health, and environmental practices and deter-
tion factor for a particular apparatus using calibration speci-
mine the applicability of regulatory limitations prior to use.
mens having known thermal transmission properties.
1.15 This international standard was developed in accor-
dance with internationally recognized principles on standard- 3.2.2 calibration transfer specimen, n—(CTS) a thermal
ization established in the Decision on Principles for the calibration specimen that has been measured by a national
Development of International Standards, Guides and Recom- standards laboratory (7).
mendations issued by the World Trade Organization Technical
3.2.3 cold surface assembly, n—the plate that provides as
Barriers to Trade (TBT) Committee.
isothermalboundaryatthecoldsurfaceofthetestspecimen(s).
3.2.4 controlled environment, n—an environment some-
2. Referenced Documents
times employed in the apparatus to limit lateral heat flows.
2.1 ASTM Standards:
3.2.5 edge insulation, n—auxiliary insulation used to limit
C167 Test Methods for Thickness and Density of Blanket or
lateralheatflows,thesearesometimespermanentlymountedin
Batt Thermal Insulations
the apparatus.
C168 Terminology Relating to Thermal Insulation
C177 Test Method for Steady-State Heat Flux Measure-
3.2.6 guard, n—promotes one-dimensional heat flow. Pri-
ments and Thermal Transmission Properties by Means of
mary guards are planar, additional coplanar guards can be used
the Guarded-Hot-Plate Apparatus
and secondary or edge guards are axial.
C236 Test Method for Steady-StateThermal Performance of
3.2.7 heat flow meter apparatus, n—the complete assem-
Building Assemblies by Means of a Guarded Hot Box
blage of the instrument, including hot and cold isothermal
(Withdrawn 2001)
surfaces, the heat flux transducer(s), and the controlled envi-
C687 Practice for Determination of Thermal Resistance of
ronment if used, and instrumentation to indicate hot and cold
Loose-Fill Building Insulation
surface temperatures, specimen thickness, and heat flux.
C976 Test Method for Thermal Performance of Building
3.2.8 hot surface assembly, n—the plate that provides an
Assemblies by Means of a Calibrated Hot Box (With-
isothermal boundary at the hot surface of the test specimen(s).
drawn 2002)
C1045 Practice for Calculating Thermal Transmission Prop-
3.2.9 heat flux transducer, n—a device containing a
erties Under Steady-State Conditions
thermopile, or an equivalent, that produces an output which is
C1046 Practice for In-Situ Measurement of Heat Flux and
afunctionoftheheatfluxpassingthroughit.Themeteringarea
Temperature on Building Envelope Components
usually consists of a number of differently connected tempera-
C1058 Practice for Selecting Temperatures for Evaluating
ture sensors placed on each face of a core and surface sheets to
and Reporting Thermal Properties of Thermal Insulation
protect the assembly.Aproperly designed transducer will have
C1114 Test Method for Steady-State Thermal Transmission
a sensitivity that is essentially independent of the thermal
Properties by Means of the Thin-Heater Apparatus
properties of the specimen.
E230/E230M Specification for Temperature-Electromotive
3.2.10 metering area, n—the area of the specimen(s) in
Force (emf) Tables for Standardized Thermocouples
contact with the sensor area of the heat flux transducer.
E178 Practice for Dealing With Outlying Observations
E456 Terminology Relating to Quality and Statistics 3.2.11 secondary transfer standard, n—a specimen, which
E691 Practice for Conducting an Interlaboratory Study to
has been measured in a heat flow meter apparatus, which has
Determine the Precision of a Test Method been calibrated with primary standards, used to calibrate
additional apparatuses.
2.2 ISO Standard:
ISO 8301:1991 Thermal Insulation—Determination of
3.2.12 sensitivity, n—the ratio of the heat flux passing
Steady-State Thermal Resistance and Related
through the transducer to the electrical output of the heat flux
Properties—Heat Flow Meter Apparatus
transducer.
3.2.13 standard reference material (SRM), n—a lot of ma-
terial that has been characterized by a national standards
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
laboratory (7).
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3.2.14 thermal transmission properties, n—those properties
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
of a material or system that define the ability of the material or
The last approved version of this historical standard is referenced on
system to transfer heat. Properties, such as thermal resistance,
www.astm.org.
thermal conductance, thermal conductivity, and thermal resis-
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. tivity would be included, as defined in Terminology C168.
C518 − 21
3.3 Symbols and Units—The symbols used in this test anisotropies, rigidity, or especially high or low resistance to
method have the following significance: heat flow (see Practice C1045). The use of a heat flow meter
3.3.1 λ—thermal conductivity, W/(m·K). apparatus when there are thermal bridges present in the
3.3.2 C—thermal conductance, W/(m ·K) specimen may yield very unreliable results. If the thermal
bridge is present and parallel to the heat flow the results
3.3.3 R—thermal resistance, (m ·K)/W.
3.3.4 q—heat flux (heat flow rate, Q, through area A), W/m . obtained may well have no meaning. Special considerations
also are necessary when the measurements are conducted at
3.3.5 Q—heat flow rate in the metered area, W.
3.3.6 A—metering area, m . either high or low temperatures, in ambient pressures above or
below atmospheric pressure, or in special ambient gases that
3.3.7 L—separation between the hot and cold plate assem-
blies during testing, m. are inert or hazardous.
3.3.8 T —mean temperature, (T +T )/2, K.
m h c
4.5 Thedeterminationoftheaccuracyofthemethodforany
3.3.9 ∆T—temperature difference across the specimen, K.
given test is a function of the apparatus design, of the related
3.3.10 ρ—(bulk) density of the material tested, kg/m .
instrumentation, and of the type of specimens under test (see
3.3.11 S—calibration factor of the heat flux transducer,
Section 10), but this test method is capable of determining
(W/m )/V.
thermal transmission properties within 6 2 % of those deter-
3.3.12 E—heat flux transducer output, V.
mined by Test Method C177 when the ambient temperature is
3.3.13 T —temperature of the hot plate surface, K.
h
near the mean temperature of the test (T (ambient) = T (mean)
3.3.14 T —temperature of the cold plate surface, K.
c
6 1°C), and in the range of 10 to 40°C. In all cases the
accuracy of the heat flow meter apparatus can never be better
3.4 Subscripts:
than the accuracy of the primary standards used to calibrate the
3.4.1 h—hot.
apparatus.
3.4.2 c—cold
4.5.1 When this test method is to be used for certification
3.4.3 a, b—first and second specimen.
testing of products, the apparatus shall have the capabilities
3.4.4 m—mean.
required in A1.7 and one of the following procedures shall be
3.4.5 α—statistical term used to define significance level.
followed:
4.5.1.1 The apparatus shall have its calibration checked
4. Significance and Use
within 24 h before or after a certification test using either
4.1 This test method provides a rapid means of determining
secondary transfer standards traceable to, or calibration stan-
the steady-state thermal transmission properties of thermal
dards whose values have been established by, a recognized
insulations and other materials with a high level of accuracy
national standards laboratory not more than five years prior to
when the apparatus has been calibrated appropriately.
the certification date. The average of two calibrations shall be
4.2 Proper calibration of the heat flow meter apparatus
usedasthecalibrationfactorandthespecimen(s)certifiedwith
requires that it be calibrated using specimen(s) having thermal
this average value. When the change in calibration factor is
transmission properties determined previously by Test Meth-
greater than 1 %, the standard specimen shall be retested and a
ods C177,or C1114.
new average calculated. If the change in calibration factor is
stillgreaterthan1 %theapparatusshallbecalibratedusingthe
NOTE 1—Calibration of the apparatus typically requires specimens that
procedure in Section 6.
are similar to the types of materials, thermal conductances, thicknesses,
mean temperatures, and temperature gradients as expected for the test
4.5.1.2 Where both the short and long term stability of the
specimens.
apparatushavebeenproventobebetterthan1 %ofthereading
4.3 The thermal transmission properties of specimens of a (see Section 10), the apparatus may be calibrated at less
frequent intervals, not exceeding 30 days. The specimens so
given material or product may vary due to variability of the
composition of the material; be affected by moisture or other tested cannot be certified until after the calibration test follow-
ing the test and then only if the change in calibration factor
conditions; change with time; change with mean temperature
and temperature difference; and depend upon the prior thermal from the previous calibration test is less than 1 %. When the
change in calibration is greater than 1 %, test results from this
history. It must be recognized, therefore, that the selection of
interval shall be considered void and the tests repeated in
typicalvaluesofthermaltransmissionpropertiesrepresentative
accordance with 4.5.1.1.
of a material in a particular application should be based on a
consideration of these factors and will not apply necessarily 4.5.2 The precision (repeatability) of measurements made
without modification to all service conditions. by the heat flow meter apparatus calibrated as in Section 6.6
4.3.1 As an example, this test method provides that the normally are much better than 61 % of the mean value. This
precision is required to identify changes in calibration and is
thermal properties shall be obtained on specimens that do not
contain any free moisture although in service such conditions desirable in quality control applications.
may not be realized. Even more basic is the dependence of the
thermal properties on variables, such as mean temperature and 5. Apparatus
temperature difference. These dependencies should be mea-
5.1 The construction guidelines given in this section should
sured or the test made at conditions typical of use.
be understood by the user of this test method. While it is
4.4 Special care shall be taken in the measurement proce- mandatory that these details be followed carefully when
dure for specimens exhibiting appreciable inhomogeneities, constructing an apparatus, it behooves the user to verify that
C518 − 21
the equipment is built as specified. Serious errors of measure-
ment may result from this oversight.
5.2 General:
5.2.1 The general features of a heat flow meter apparatus
with the specimen or the specimens installed are described in
Section 6 and shown in Figs. 1-3.Aheat flow meter apparatus
consists of two isothermal plate assemblies, one or more heat
flux transducers and equipment to control the environmental
conditions when needed. Each configuration will yield equiva-
lent results if used within the limitations stated in this test
method.Therearedistinctadvantagesforeachconfigurationin
practice and these are discussed in Appendix X2.
NOTE 2—Further information can be found in ISO 8301:1991, which is
the equivalent ISO standard for the Heat Flow Meter Apparatus.
5.2.2 Further design considerations such as plate surface
treatment, flatness and parallelism, temperature requirements
andmeasuringsystemrequirementscanbefoundinAnnexA1.
FIG. 2 Apparatus with One Heat Flux Transducer and Two
6. Calibration Specimens
6.1 The calibration of a heat flow meter apparatus is a very
critical operation. Since lateral heat losses or gains of heat are
not controlled or eliminated automatically, but only lessened
by increasing the size of the guard area and edge insulation,
there is no guarantee that the heat losses or gains are negligible
under all testing conditions. To ensure that the equipment is
performing properly with specimens of different thermal
FIG. 3 Apparatus with Two Heat Flux Transducers and One
resistances, the apparatus shall be calibrated with materials
Specimen
having similar thermal characteristics and thicknesses as the
materials to be evaluated. The apparatus shall be calibrated
with the specimen in the same orientation and the heat flux in
the same direction under which the primary, CTS or SRM, or
6.4.1 Calibration standards may be good for many years if
secondarytransferstandardswerecharacterized,ifknown.The
handled carefully but shall be checked periodically to confirm
material selected for the calibration standard shall have prop-
lack of change.
erties that are not affected by convection over the range of
6.4.2 It is recommended that the primary standards obtained
calibration parameters (temperature difference, thickness,
from a national standards laboratory should not be used on a
density, and so forth) of interest. The apparatus shall be
daily basis, but secondary or working standards should be
calibrated as a unit, with the heat flux transducer(s) installed in
produced. Create a record on the secondary standards with the
the apparatus.
following information.
6.2 This procedure applies to the calibration of a heat flow
6.4.2.1 Name of national laboratory to which it is traceable.
meter apparatus over a wide range of heat flow rates and 6.4.2.2 Date the secondary standard is produced.
temperatures, which permits the testing of a wide variety of 6.4.2.3 Date the secondary standard is last tested.
insulation materials over an extended temperature range.
6.4.2.4 Direction of heat flux during calibration.
6.4.2.5 Thermal value of the secondary standard.
6.3 The following calibration procedure is used to compute
6.4.2.6 Range of parameters for which it is valid.
the calibration factor, S for a heat flow meter apparatus, and
6.4.2.7 Estimate of bias of the primary and secondary
must be used by anyone who desires to produce meaningful
standards.
heat flux measurements from a heat flow apparatus.
6.5 Calibration Procedure:
6.4 Calibration Standards:
6.5.1 Calibratetheheatflowmeterapparatusunderthesame
conditions of plate temperatures, temperature gradient, speci-
menthickness,heatflowdirection,andapparatusorientationas
those for which data are available for the standard.
6.5.2 Single Temperature Point—If the calibration standard
is tested at a single mean temperature, conduct the calibration
and subsequent tests near the same mean temperature. Use
engineering judgment or an error analysis to determine how
closely the mean temperature must be maintained. As assess-
FIG. 1 Apparatus with One Heat Flux Transducer and One
Specimen ment of the sensitivity of the calibration standard to test
C518 − 21
conditions should be determined by the user of the transfer 6.6.3.2 Two Calibration Standards—Apparatus with one
standard to determine its limitations of use. heat flux transducer and two specimens (see Fig. 2).
6.6.3.3 Again, the standards need to be the same thickness
6.5.3 Multiple Temperature Points—If the calibration stan-
dard is tested at three or more mean temperatures, calibrate the and of similar material but not necessarily identical.
heat flow meter apparatus at the same temperatures using the
C 1C
a b
S 5 (3)
sametemperaturegradients (8).Asmoothcurvecanbefittedto
1 1
E· 1
S D
the points such that a calibration factor can be interpolated for
T 2 T T 2 T
~ ! ~ !
ha ca hb cb
any given mean temperature. It is not permissible to extrapo-
6.6.4 One Calibration Standard—Apparatus with two heat
late above or below the mean temperature range of the
flux transducers and one specimen (see Fig. 3).
calibration standard measurements. Changing the plate tem-
6.6.4.1 Assuming the two transducers physically are iden-
perature of a heat flow meter apparatus has the potential of
tical and have similar outputs, one can sum the outputs of the
changing apparatus calibration. When changing plate
two transducers and then calibrate as a single transducer
temperatures,takestepstodetermineiftheheatfluxtransducer
apparatus. In this case, it is very important to keep the mean
calibration factor has changed.
temperature and the plate temperatures equal to those used in
6.5.4 Single Thickness Point—If the original calibration
testing the standard. It is essential that each of the transducers
standard is tested at only one thickness, the heat flow meter
be at steady state.
apparatus can be calibrated for that thickness without an
exhaustive thickness study. If tests are to be conducted at
C· Th 2 Tc
~ !
S 5 (4)
thicknesses other than the calibrated thickness, make a thor-
E11E2
~ !
oughstudyoftheerroroftheheatflowmeterapparatusatother
6.6.4.2 In the case where multiple transducers are used, a
thicknesses. Several references on this subject are listed at the
similar calculation can be utilized to calculate the calibration
end of this test method (4, 7-10).
factor.
6.5.5 Multiple Thickness Points—If the original standard is
6.6.4.3 As an alternative, each heat flux transducer can be
tested at three or more thicknesses, the heat flow meter
calibrated as an independent apparatus as in 6.6.1.
apparatus can be calibrated over the same thickness range. A
smooth curve can be fitted to the points such that a calibration
7. Test Procedures
factor can be interpolated for any given thickness. If tests are
7.1 Foreword on Testing Procedures—The relative simplic-
to be conducted at thicknesses above or below the calibrated
thicknesses,makeathoroughstudyoftheerroroftheheatflow ity of this test method may lead one to overlook very important
factors, which may affect the results. To ensure accurate
meter apparatus at these thicknesses.
measurement, the operator shall be instructed fully in the
6.6 Calibration of Various Designs:
operation of the equipment. Furthermore, the equipment shall
6.6.1 There are several configurations of heat flow meter
be calibrated properly with reference materials having similar
apparatuses that use one or two heat flux transducers and one
heat transfer characteristics. Also it is necessary that the
or two specimens in the apparatus. While it is not practical to
specimen be prepared properly for evaluation.
list all of the possible combinations of apparatus and specimen
7.2 Sampling and Preparation of Specimens:
configurations, this section contains the equations for calculat-
7.2.1 Test Specimens—One- or two-piece specimens may be
ing the calibration factor of three common apparatuses. The
used, depending on the configuration selected for the test.
calibration and testing configuration should be identical. The
Where two pieces are used, they shall be selected from the
calibration factor of a heat flow meter apparatus is determined
same material to be essentially identical in construction,
byrunningthesamestandardspecimensanumberoftimes,not
thickness, and density. For loose fill materials, the method
consecutively, but over a period of time with the standard
specified in the material specification or in Practice C687 shall
removed each time.
be used to produce a specimen or specimens of the desired
6.6.2 One Calibration Standard—Apparatus with one heat
density.
flux transducer and one standard (see Fig. 1).
7.2.2 Selection of Specimens—The specimen or specimens
S 5 C·~Th 2 Tc!/E (1)
shallbeofsuchsizeastocovertheplateassemblysurfacesand
6.6.3 Two Calibration Standards—Apparatus with one heat
shall either be of the actual thickness to be applied in use or of
flux transducer and one specimen configuration (same as that sufficient thickness to give a true average representation of the
for 6.6.2).
material to be tested. If sufficient material is not available, the
6.6.3.1 The two calibration standards need to be the same specimen shall at least cover the metering area, and the rest of
thickness and of similar material but need not be identical. the plate surfaces must be covered with a mask with a thermal
With the following equation, it is not necessary to know the conductivity as close to that of the specimen as possible.
thermal conductance of each calibration standard, but it is
7.3 Specimen Conditioning—Details of the specimen selec-
necessary to know the average thermal conductance of the two
tion and conditioning preferably are given in the material
standards:
specification. Where such specifications are not given, the
C 1C specimen preparation shall be conducted in accordance with
a b
S 5 (2)
E E the requirement that materials shall not be exposed to tempera-
a b
S D
T 2 T T 2 T tures that will change the specimens in an irreversible manner.
~ ! ~ !
ha ca hb cb
C518 − 21
Typically, the material specifications call for specimen condi- construction of the heat meter apparatus, and the properties of
tioning at 22°C and 50 % R.H. for a period of time until less the specimen. No suitable theoretical analysis is available to
than a 1 % mass change is observed over a 24-h period. For predict the maximum allowable thickness of specimens. It is
some materials, such as cellulose, considerably longer times possible to use the results of an analysis for a similarly sized
may be required for both conditioning and testing. guarded hot plate as a guide (11-14).
7.7 Procedure of Measurement:
7.4 Specimen Preparation:
7.7.1 Temperature Difference—For any test, make the tem-
7.4.1 Use the following guidelines when the material speci-
perature difference across the specimen not less than 10 K. For
fication is unavailable. In general, the surfaces of the specimen
specimens that are expected to have a large thermal resistance,
should be prepared to ensure that they are parallel with and
a larger temperature difference in the specimen is recom-
have uniform thermal contact with the hot and cold plates.
mended (see Practice C1058 for the selection of the plate
7.4.2 Compressible Specimens—The surfaces of the uncom-
temperatures). The actual temperature difference or gradient is
pressed specimens may be comparatively uneven so long as
best specified in the material specifications or by agreement of
surface undulations are removed under test compression. It
the parties concerned.
may be necessary to smooth the specimen surfaces to achieve
7.7.2 Edge Insulation—Enclose the edges of the specimens
better plate-to-specimen contact. If the apparent thermal con-
with thermal insulation to reduce edge heat losses to an
ductivity of the contact void is greater than that of the
acceptable level if this edge insulation is not built into the
specimen, compressible or otherwise, the measured heat flux
apparatus (see A1.6).
will be greater than the heat flux that would be obtained if the
7.7.3 Settling Time and Measurement Interval—Verify the
voids were absent. This may often be the case at higher
existence of thermal equilibrium by observing and recording,
temperatures where radiant heat transfer predominates in the
the emf output of the heat flux transducer, the mean tempera-
void. For the measurement of compressible specimens, the
ture of the specimens, the temperature drop across the
temperature sensors are often mounted directly in the plate
specimen, and a calculated λ value. Make observations at time
surfaces.Also, plate spacers may be required for the measure-
intervals of at least 10 min until five successive observations
ment of compressible specimens.
yield values of thermal conductivity, which fall within ⁄2%of
7.4.3 Rigid and High Conductance Specimens—The mea-
the mean value for these five readings. If the five readings
surement of rigid specimens or high conductance specimens
show a monotonically increasing or decreasing trend, equilib-
requires careful surface preparation. First, the surfaces should
rium has not been attained. In this case, additional sets of
be made flat and parallel to the same degree as the heat-flow-
readings shall be taken. If experience has shown that a shorter
meter. If the specimen has a thermal resistance that is suffi-
timeintervalmaybeused,followthesamecriteriaforstability.
ciently high compared to the specimen-to-plate interface
For high density specimens (ρ > 40 kg/m ) or for low
resistance, temperature sensors mounted in the plates may be
conductance specimens (C < 0.05 W/K·m ) the time between
adequate.
readings may have to be increased to 30 min or longer (15).
7.5 Measurements on Specimens:
7.5.1 BlanketandBatt-TypeMaterials—Whenspecified,the
8. Calculation
test thickness of blankets and batt-type materials shall be
8.1 Density and Change in Mass—When required, calculate
determined before testing in accordance with Test Methods
the density of the dry specimen as tested, ρ, the mass change
C167, provided that good contact is maintained between the
due to conditioning of the material, and the mass change of the
specimen and the isothermal plates. Also, it is recommended
specimen during test.
highly that the thickness during the actual test be measured.At
8.1.1 Density of Batt and Blanket Specimens—It has been
the conclusion of the test, the density in the metering area
found that it is important to measure the mass of the specimens
should be determined.
in contact with the metering area. The area of the specimen
7.5.2 Loose-fill Materials—These materials generally are
directlymeasuredshallbecutoutanditsmassdeterminedafter
tested in open test frames as spelled out in Practice C687. The
testing, unless the specimen must be retained for further
requirement to measure the density in the metering area is
testing.
again critical.
8.2 Thermal Properties for One Specimen—When only one
7.6 Limitations on Specimen Thickness:
specimen is used, calculate the thermal conductance of the
7.6.1 General—The combined thickness of the specimen or
specimen as follows:
specimens, the heat flux transducer and any damping material,
C 5 S·E/∆T (5)
which in total equals the distance between the cold and hot
plates, must be restricted in order to limit the effect of edge
and where applicable, calculate the thermal conductivity, as
losses on the measurements. In addition edge losses are
follows:
affected by the edge insulation and the ambient temperature, so
λ 5 S·E·~L/∆T! (6)
the requirements on both of these parameters must be met.
8.3 Thermal Properties for Two Specimens—When two
7.6.2 Maximum Spacing Between Hot and Cold Plates—
specimens are used, calculate the total thermal conductance, C,
The maximum allowable distance between the hot and cold
as follows:
plates during a test, is related to the dimensions of the heat flux
transducer,themeteringarea,thesizeoftheplateassembly,the C 5 S·E/ ∆T 1∆T (7)
~ !
a b
C518 − 21
The λ factor, that is, the average thermal conductivity of the 9.2 In many cases a laboratory is requested to provide only
specimen is calculated as follows: the thermal conductivity at a specified mean temperature and a
few pertinent physical properties, such as density, and test
λ 5 S·E/2 · L 1L / ∆T 1∆T (8)
~ ! ~ ! ~ !
ave a b a b
thickness.An abridged test report shall state “AbridgedASTM
where the subscripts refer to the two specimens.
C518 Test Report” and shall include the thermal transmission
property of interest, mean temperature, test thickness, and bulk
8.4 Other derived thermal properties may be calculated but
density. It is mandated that an uncertainty statement shall be
only under the provisions given in Practice C1045.
transmitted with the thermal transmission property. Compli-
8.5 Thermal Properties for Two Transducers—All pertinent
ance to Test Method C518 requires that the other test param-
equations of 8.2 and 8.3 apply to this configuration, provided
eters specified in 9.1.1 – 9.4 to be recorded in the laboratory
S·E will be replaced by (S’·E’ + S”·E”)/2, where the super-
records.
scripts ’ and ” refer to the first and second heat flux transducer,
9.3 For certification testing only, the specimens used in
respectively.
calibration shall be identified as to the type, thermal resistance,
date of specimen certification, source of certification, expira-
9. Report
tion date of calibration, and the certification test number.
9.1 The report of the results of each test shall include the
Whereapplicableincludeastatementofthelaboratoryaccredi-
following information with all data to be reported in both SI
tation of the test facility, including the date of the latest
and inch-pound units unless specified otherwise.
inspection.
9.1.1 Thereportshallbeidentifiedwithauniquenumbering
9.4 Statement of compliance, or where circumstances or
system to allow traceability back to the individual measure-
requirements preclude complete compliance with the proce-
ments taken during the test performed.
dures of the test, agreed exceptions. A suggested wording is
9.1.2 Name and any other pertinent identification of the
“This test conformed with all requirements of ASTM C518
material including a physical description.
with the exception of (a complete list of exceptions follows).”
9.1.3 Description of the specimen and its relationship to the
sample, including a brief history of the specimen, if known.
10. Precision and Bias
9.1.4 Thickness of the specimen as received and as tested.
10.1 This section on precision and bias for heat flow meter
9.1.5 Method and environment used for conditioning, if
apparatus includes a discussion of; general statistical terms;
used.
statistical control; factors affecting test results; ruggedness
9.1.6 Density of the conditioned specimen as tested, kg/m .
tests; interlaboratory comparisons conducted by ASTM Com-
9.1.7 Mass loss of the specimen during conditioning and
mitteeC16;proficiencytestingconductedundertheauspicesof
testing, in percentage of conditioned mass, if measured.
theNationalVoluntaryLaboratoryAccreditationProgram(NV-
9.1.8 Mass regain of the specimen during test, in percentage
LAP); and error propagation formulae.
of conditioned mass, if measured.
10.2 The accuracy of a test result refers to the closeness of
9.1.9 Average temperature gradient in the specimen during
agreement between the observed value and an accepted refer-
test as computed from the temperatures of the hot and cold
ence value. When applied to a set of observed values, the
surfaces, K/m.
accuracy includes a random component (imprecision) and a
9.1.10 Mean temperature of the test, K or °C.
systematic component (bias). The variability associated with
9.1.11 Heat flux amount and direction through the
2 the set of observed values is an indication of the uncertainty of
specimen, W/m .
2 the test result. Additional information on statistical terminol-
9.1.12 Thermal conductance, W/m · K.
ogy is available in Terminology .
9.1.13 Duration of the measurement portion of the test, min
10.3 The user of the heat-flow-meter apparatus shall dem-
or h.
onstrate that the apparatus is capable of performing in a
9.1.14 For loose-fill materials, report the specimen prepara-
consistent manner over time (16, 17).The use of control charts
tion followed.
(see Manual 7 (18)) to monitor the operation of the heat-flow-
9.1.15 Date of test, the date of the last heat meter
meter is one recommended way to monitor the control stability
calibration, and the type or types of materials used.
of the apparatus. When possible, it is recommended that a
9.1.16 Estimated or calculated uncertainty in reported val-
reference material traceable to a national standards laboratory
ues. It is optional as to which of the error analysis methods
be used as the control specimen. Ideally, the long-term varia-
given in Annex A2 is used by the laboratory.
tion should be no greater than the short-term variability.
9.1.17 Orientation and position of the heat meter apparatus
during test (vertical, horizontal, etc.), and whether the meter
10.4 A series of three round robins was conducted between
was against the hot or cold surface of the specimen and 1976 and 1983, as reported by Hust and Pelanne (19), and
whether the edges of the specimen(s) were sealed or open to
employed low density fiberglass specimens from 2.54 to 10.2
the ambient. cm. thick with densities ranging from 10 to 33 kg/m . A total
9.1.18 For direct reading apparatus, the results of the of twelve laboratories were involved in these studies. The
calibration of electronic circuitry and equipment or a statement interlaboratory imprecision, at the two standard deviation level
of compliance including date, and a statement of compliance when analyzed using Practice E691, was found to vary from
on linearity requirements. 1.92 to 3.54 % between 2.54 and 10.2 cm.
C518 − 21
TABLE 1 Summary of Precision Statistics for Thermal Resistivity Reproducibility
Reproducibility
Reproducibility
A
Average Standard
B
Material
Limit
A
(mK/W)
Deviation
(mK/W)
(mK/W)
x¯ S R
R
A (n=13) 29.76 0.31 0.88
2.94 %
B (n=13) 30.02 0.27 0.75
2.50 %
A
Calculated from all reporting laboratories (n=13 for materials A & B).
B
95 % reproducibility limit is 2.8 times the reproducibility standard deviation (between laboratory).
TABLE 2 Summary of Precision Statistics for Thermal Resistivity Repeatability
Repeatability
Repeatability
A
Average Standard
B
Material
Limit
A
(mK/W)
Deviation
(mK/W)
(mK/W)
x¯ S r
r
A (n=10) 29.73 0.18 0.50
1.68 %
B (n=8) 29.99 0.15 0.41
1.37 %
A
Calculated from all reporting laboratories (n=10 for material A, n=8 for material B).
B
95 % repeatability limit is 2.8 times the repeatability standard deviation (within laboratory).
10.5 A round robin conducted in 1987, as reported by the Test Method C177 apparatus was found to be statistically
Adams and Hust, included eleven participating laboratories insignificantatthe α=5 %level(95 %confidenceinterval)for
testing a fiberglass blanket and several types of loose-fill the materials studied.
insulations (20). The blanket insulation had an interlaboratory
10.8 Proficiency Tests—Interlaboratory testing carried out
imprecision of 3.7 % at the two standard deviation level. The
between nine laboratories under the National Voluntary Labo-
loose-fill interlaboratory imprecision was found to be > 10 %
ratory Accreditation Program currently is showing an inter-
fordifferentmaterialsatthetwostandarddeviationlevel.Ithas
laboratory imprecision of 2.12 % at the two standard deviation
been suggested that the principal cause for the significant
level based on testing of similar but not identical specimens
differences observed is the various specimen preparation tech-
(23, 24).
niques used by the various laboratories.
10.9 An interlaboratory study was performed in 2002-
10.6 A round robin conducted in 1990, as reported by
2004. A total of thirteen laboratories participated in the study,
McCaa and Smith, et. al., included ten participating laborato-
testing two specimens for both thickness and thermal resistiv-
ries testing a fiberglass blanket and several type of loose-fill
ity. Two 25 mm thick expanded polystyrene (EPS) foam board
insulation (21). The blanket insulation had an interlaboratory
specimen (A and B) of similar thickness and thermal perfor-
imprecision of 2.8 % at the two standard deviation level. The
mance were used for this study. Each test result was to be
loose-fillinterlaboratoryimprecisionwasfoundtobe5.0 %for
repeated for a total of two determinations. The precision and
perlite, 5.8 % for cellulose, 9.4 % for unbonded fiberglass, and
bias statements were determined through statistical examina-
10.5 % for mineral wool at the two standard deviation level.
tion of two individual results, from the participating
This represented a significant improvement over the 1987
laboratories, on two samples. The results are shown in Table 1
resultsandisattributedtoamoreconcisespecimenpreparation
and Table 2.
procedure in Practice C687.
11. Keywords
10.7 An Interlaboratory “Pilot Run” of Small Heat-Flow-
MeterApparatus forASTM C518 was reported in 1999 (22).A
11.1 calibration; error analysis; heat flow meter apparatus,
precision statement was prepared in accordance with Practice
thermal resistance; heat flux; instrument verification; thermal
E691. The precision statement is provisional because an
conductivity; thermal testing
insufficient number of materials were involved. Within 5 years
additional data will be obtained and processed that meet the
Supporting data have been filed at ASTM International Headquarters and may
requirements of Practice E691. A bias statement was prepared
beobtainedbyrequestingResearchReportRR:C16-1047.ContactASTMCustomer
followingTest Method C177. Bias as compared to results from Service at [e-mail].
C518 − 21
ANNEXES
(Mandatory Information)
A1. EQUIPMENT DESIGN
A1.1 The exposed surfaces of the plates and the heat flux A1.2.4 Plate flatness may become critical when measuring
transducer, that is, the surfaces making contact with the specimens with less thermal resistance than the calibration
specimens, shall be painted or otherwise treated to have a total standards, irrespective of the thickness or rigidity of the
hemispherical emittance of greater than 0.8 at their operating calibration standard. For rigid thin specimens the criteria given
temperatures (see Note A1.1). in A1.2.3 may not be sufficient.
NOTE A1.1—Hard anodizing of aluminum produces a surface with a
A1.2.5 The rigidity, flatness, and parallelism of the plates
total hemispherical emittance of approximately 0.85. Several paints are
may impede the testing of rigid specimens where it is not
available, which when applied as directed, produce a total hemispherical
emittance of approximately 0.86. possible to obtain good surface contact. In such cases, the use
of a thin sheet of suitable homogeneous material may be
A1.2 Plate Assemblies, Hot and Cold—The two plate as-
interposed between the specimen and the plates surfaces. This
semblies should provide isothermal surfaces in contact with
thin sheet should have a low thermal resistance relative to the
either side of the test specimen. The assemblies consist of heat
specimen. The resistance of the thin sheet should be deter-
source or sink, a high conductivity surface, means to measure
mined using a Test Method C177 apparatus. The resistance of
surface temperature, and means of support. A heat flux trans-
the composite sandwich (sheet-rigid specimen-sheet) then is
ducer may be attached to one, both, or neither plate assembly,
determined and the value of the sheet resistance subtracted
depending upon the design, (see Section 6). In all cases, the
from the total resistance. Caution should be exercised when
area defined by the sensor of the heat flux transducer is called
using such a practice as it is prone to adding more uncertainty
the metering area and the remainder of the plate is the guard
to this method.
area.
A1.3 Temperature Measuring and Control Systems
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C518 − 17 C518 − 21
Standard Test Method for
Steady-State Thermal Transmission Properties by Means of
the Heat Flow Meter Apparatus
This standard is issued under the fixed designation C518; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the measurement of steady state thermal transmission through flat slab specimens using a heat flow
meter apparatus.
1.2 The heat flow meter apparatus is used widely because it is relatively simple in concept, rapid, and applicable to a wide range
of test specimens. The precision and bias of the heat flow meter apparatus can be excellent provided calibration is carried out within
the range of heat flows expected. This means calibration shall be carried out with similar types of materials, of similar thermal
conductances, at similar thicknesses, mean temperatures, and temperature gradients, as expected for the test specimens.
1.3 This a comparative, or secondary, method of measurement since specimens of known thermal transmission properties shall be
used to calibrate the apparatus. Properties of the calibration specimens must be traceable to an absolute measurement method. The
calibration specimens should be obtained from a recognized national standards laboratory.
1.4 The heat flow meter apparatus establishes steady state one-dimensional heat flux through a test specimen between two parallel
plates at constant but different temperatures. By appropriate calibration of the heat flux transducer(s) with calibration standards and
by measurement of the plate temperatures and plate separation. Fourier’s law of heat conduction is used to calculate thermal
conductivity, and thermal resistivity or thermal resistance and thermal conductance.
1.5 This test method shall be used in conjunction with Practice C1045. Many advances have been made in thermal technology,
both in measurement techniques and in improved understanding of the principles of heat flow through materials. These advances
have prompted revisions in the conceptual approaches to the measurement of the thermal transmission properties (1-4). All users
of this test method should be aware of these concepts.
1.6 This test method is applicable to the measurement of thermal transmission through a wide range of specimen properties and
environmental conditions. The method has been used at ambient conditions of 10 to 40°C with thicknesses up to approximately
250 mm, and with plate temperatures from –195°C to 540°C at 25-mm thickness (5, 6).
1.7 This test method may be used to characterize material properties, which may or may not be representative of actual conditions
of use. Other test methods, such as Test Methods C236 or C976 should be used if needed.
This test method is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved May 1, 2017Sept. 1, 2021. Published July 2017September 2021. Originally approved in 1963. Last previous edition approved in 20152017 as
C518 – 15.C518 – 17. DOI: 10.1520/C0518-17.10.1520/C0518-21.
The boldface numbers in parentheses refer to the list of references at the end of this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C518 − 21
1.8 To meet the requirements of this test method the thermal resistance of the test specimen shall be greater than 0.10 m ·K/W
in the direction of the heat flow and edge heat losses shall be controlled, using edge insulation, or a guard heater, or both.
1.9 It is not practical in a test method of this type to try to establish details of construction and procedures to cover all
contingencies that might offer difficulties to a person without pertinent technical knowledge. Thus users of this test method shall
have sufficient knowledge to satisfactorily fulfill their needs. For example, knowledge of heat transfer principles, low level
electrical measurements, and general test procedures is required.
1.10 The user of this method must be familiar with and understand the Annex. The Annex is critically important in addressing
equipment design and error analysis.
1.11 Standardization of this test method is not intended to restrict in any way the future development of improved or new methods
or procedures by research workers.
1.12 Since the design of a heat flow meter apparatus is not a simple matter, a procedure for proving the performance of an
apparatus is given in Appendix X3.
1.13 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.14 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to consult and establish appropriate safety safety, health, and healthenvironmental practices and
determine the applicability of regulatory limitations prior to use.
1.15 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C167 Test Methods for Thickness and Density of Blanket or Batt Thermal Insulations
C168 Terminology Relating to Thermal Insulation
C177 Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the
Guarded-Hot-Plate Apparatus
C236 Test Method for Steady-State Thermal Performance of Building Assemblies by Means of a Guarded Hot Box (Withdrawn
2001)
C687 Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
C976 Test Method for Thermal Performance of Building Assemblies by Means of a Calibrated Hot Box (Withdrawn 2002)
C1045 Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
C1046 Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components
C1058 Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation
C1114 Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
E230/E230M Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
E178 Practice for Dealing With Outlying Observations
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standard:
ISO 8301:1991 Thermal Insulation—Determination of Steady-State Thermal Resistance and Related Properties—Heat Flow
Meter Apparatus
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
C518 − 21
3. Terminology
3.1 Definitions—For definitions of terms and symbols used in this test method, refer to Terminology C168 and to the following
subsections.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration, n—the process of establishing the calibration factor for a particular apparatus using calibration specimens having
known thermal transmission properties.
3.2.2 calibration transfer specimen, n—(CTS) a thermal calibration specimen that has been measured by a national standards
laboratory (7).
3.2.3 cold surface assembly, n—the plate that provides as isothermal boundary at the cold surface of the test specimen(s).
3.2.4 controlled environment, n—an environment sometimes employed in the apparatus to limit lateral heat flows.
3.2.5 edge insulation, n—auxiliary insulation used to limit lateral heat flows, these are sometimes permanently mounted in the
apparatus.
3.2.6 guard, n—promotes one-dimensional heat flow. Primary guards are planar, additional coplanar guards can be used and
secondary or edge guards are axial.
3.2.7 heat flow meter apparatus, n—the complete assemblage of the instrument, including hot and cold isothermal surfaces, the
heat flux transducer(s), and the controlled environment if used, and instrumentation to indicate hot and cold surface temperatures,
specimen thickness, and heat flux.
3.2.8 hot surface assembly, n—the plate that provides an isothermal boundary at the hot surface of the test specimen(s).
3.2.9 heat flux transducer, n—a device containing a thermopile, or an equivalent, that produces an output which is a function of
the heat flux passing through it. The metering area usually consists of a number of differently connected temperature sensors placed
on each face of a core and surface sheets to protect the assembly. A properly designed transducer will have a sensitivity that is
essentially independent of the thermal properties of the specimen.
3.2.10 metering area, n—the area of the specimen(s) in contact with the sensor area of the heat flux transducer.
3.2.11 secondary transfer standard, n—a specimen, which has been measured in a heat flow meter apparatus, which has been
calibrated with primary standards, used to calibrate additional apparatuses.
3.2.12 sensitivity, n—the ratio of the heat flux passing through the transducer to the electrical output of the heat flux transducer.
3.2.13 standard reference material (SRM), n—a lot of material that has been characterized by a national standards laboratory (7).
3.2.14 thermal transmission properties, n—those properties of a material or system that define the ability of the material or system
to transfer heat. Properties, such as thermal resistance, thermal conductance, thermal conductivity, and thermal resistivity would
be included, as defined in Terminology C168.
3.3 Symbols and Units—The symbols used in this test method have the following significance:
3.3.1 λ—thermal conductivity, W/(m·K).
3.3.2 C—thermal conductance, W/(m ·K)
3.3.3 R—thermal resistance, (m ·K)/W.
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3.3.4 q—heat flux (heat flow rate, Q, through area A), W/m .
3.3.5 Q—heat flow rate in the metered area, W.
3.3.6 A—metering area, m .
3.3.7 L—separation between the hot and cold plate assemblies during testing, m.
3.3.8 T —mean temperature, (T + T )/2, K.
m h c
3.3.9 ΔT—temperature difference across the specimen, K.
3.3.10 ρ—(bulk) density of the material tested, kg/m .
3.3.11 S—calibration factor of the heat flux transducer, (W/m )/V.
3.3.12 E—heat flux transducer output, V.
3.3.13 T —temperature of the hot plate surface, K.
h
3.3.14 T —temperature of the cold plate surface, K.
c
3.4 Subscripts:
3.4.1 h—hot.
3.4.2 c—cold
3.4.3 a, b—first and second specimen.
3.4.4 m—mean.
3.4.5 α—statistical term used to define significance level.
4. Significance and Use
4.1 This test method provides a rapid means of determining the steady-state thermal transmission properties of thermal insulations
and other materials with a high level of accuracy when the apparatus has been calibrated appropriately.
4.2 Proper calibration of the heat flow meter apparatus requires that it be calibrated using specimen(s) having thermal transmission
properties determined previously by Test Methods C177, or C1114.
NOTE 1—Calibration of the apparatus typically requires specimens that are similar to the types of materials, thermal conductances, thicknesses, mean
temperatures, and temperature gradients as expected for the test specimens.
4.3 The thermal transmission properties of specimens of a given material or product may vary due to variability of the composition
of the material; be affected by moisture or other conditions; change with time; change with mean temperature and temperature
difference; and depend upon the prior thermal history. It must be recognized, therefore, that the selection of typical values of
thermal transmission properties representative of a material in a particular application should be based on a consideration of these
factors and will not apply necessarily without modification to all service conditions.
4.3.1 As an example, this test method provides that the thermal properties shall be obtained on specimens that do not contain any
free moisture although in service such conditions may not be realized. Even more basic is the dependence of the thermal properties
on variables, such as mean temperature and temperature difference. These dependencies should be measured or the test made at
conditions typical of use.
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4.4 Special care shall be taken in the measurement procedure for specimens exhibiting appreciable inhomogeneities, anisotropies,
rigidity, or especially high or low resistance to heat flow (see Practice C1045). The use of a heat flow meter apparatus when there
are thermal bridges present in the specimen may yield very unreliable results. If the thermal bridge is present and parallel to the
heat flow the results obtained may well have no meaning. Special considerations also are necessary when the measurements are
conducted at either high or low temperatures, in ambient pressures above or below atmospheric pressure, or in special ambient
gases that are inert or hazardous.
4.5 The determination of the accuracy of the method for any given test is a function of the apparatus design, of the related
instrumentation, and of the type of specimens under test (see Section 10), but this test method is capable of determining thermal
transmission properties within 6 2 % of those determined by Test Method C177 when the ambient temperature is near the mean
temperature of the test (T (ambient) = T (mean) 6 1°C), and in the range of 10 to 40°C. In all cases the accuracy of the heat flow
meter apparatus can never be better than the accuracy of the primary standards used to calibrate the apparatus.
4.5.1 When this test method is to be used for certification testing of products, the apparatus shall have the capabilities required
in A1.7 and one of the following procedures shall be followed:
4.5.1.1 The apparatus shall have its calibration checked within 24 h before or after a certification test using either secondary
transfer standards traceable to, or calibration standards whose values have been established by, a recognized national standards
laboratory not more than five years prior to the certification date. The average of two calibrations shall be used as the calibration
factor and the specimen(s) certified with this average value. When the change in calibration factor is greater than 1 %, the standard
specimen shall be retested and a new average calculated. If the change in calibration factor is still greater than 1 % the apparatus
shall be calibrated using the procedure in Section 6.
4.5.1.2 Where both the short and long term stability of the apparatus have been proven to be better than 1 % of the reading (see
Section 10), the apparatus may be calibrated at less frequent intervals, not exceeding 30 days. The specimens so tested cannot be
certified until after the calibration test following the test and then only if the change in calibration factor from the previous
calibration test is less than 1 %. When the change in calibration is greater than 1 %, test results from this interval shall be
considered void and the tests repeated in accordance with 4.5.1.1.
4.5.2 The precision (repeatability) of measurements made by the heat flow meter apparatus calibrated as in Section 6.6 normally
are much better than 61 % of the mean value. This precision is required to identify changes in calibration and is desirable in quality
control applications.
5. Apparatus
5.1 The construction guidelines given in this section should be understood by the user of this test method. While it is mandatory
that these details be followed carefully when constructing an apparatus, it behooves the user to verify that the equipment is built
as specified. Serious errors of measurement may result from this oversight.
5.2 General:
5.2.1 The general features of a heat flow meter apparatus with the specimen or the specimens installed are described in Section
6 and shown in Figs. 1-3. A heat flow meter apparatus consists of two isothermal plate assemblies, one or more heat flux
transducers and equipment to control the environmental conditions when needed. Each configuration will yield equivalent results
if used within the limitations stated in this test method. There are distinct advantages for each configuration in practice and these
are discussed in Appendix X2.
FIG. 1 Apparatus with One Heat Flux Transducer and One
Specimen
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FIG. 2 Apparatus with One Heat Flux Transducer and Two
Specimens
FIG. 3 Apparatus with Two Heat Flux Transducers and One Specimen
NOTE 2—Further information can be found in ISO 8301:1991, which is the equivalent ISO standard for the Heat Flow Meter Apparatus.
5.2.2 Further design considerations such as plate surface treatment, flatness and parallelism, temperature requirements and
measuring system requirements can be found in Annex A1.
6. Calibration
6.1 The calibration of a heat flow meter apparatus is a very critical operation. Since lateral heat losses or gains of heat are not
controlled or eliminated automatically, but only lessened by increasing the size of the guard area and edge insulation, there is no
guarantee that the heat losses or gains are negligible under all testing conditions. To ensure that the equipment is performing
properly with specimens of different thermal resistances, the apparatus shall be calibrated with materials having similar thermal
characteristics and thicknesses as the materials to be evaluated. The apparatus shall be calibrated with the specimen in the same
orientation and the heat flux in the same direction under which the primary, CTS or SRM, or secondary transfer standards were
characterized, if known. The material selected for the calibration standard shall have properties that are not affected by convection
over the range of calibration parameters (temperature difference, thickness, density, and so forth) of interest. The apparatus shall
be calibrated as a unit, with the heat flux transducer(s) installed in the apparatus.
6.2 This procedure applies to the calibration of a heat flow meter apparatus over a wide range of heat flow rates and temperatures,
which permits the testing of a wide variety of insulation materials over an extended temperature range.
6.3 The following calibration procedure is used to compute the calibration factor, S for a heat flow meter apparatus, and must be
used by anyone who desires to produce meaningful heat flux measurements from a heat flow apparatus.
6.4 Calibration Standards:
6.4.1 Calibration standards may be good for many years if handled carefully but shall be checked periodically to confirm lack of
change.
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6.4.2 It is recommended that the primary standards obtained from a national standards laboratory should not be used on a daily
basis, but secondary or working standards should be produced. Create a record on the secondary standards with the following
information.
6.4.2.1 Name of national laboratory to which it is traceable.
6.4.2.2 Date the secondary standard is produced.
6.4.2.3 Date the secondary standard is last tested.
6.4.2.4 Direction of heat flux during calibration.
6.4.2.5 Thermal value of the secondary standard.
6.4.2.6 Range of parameters for which it is valid.
6.4.2.7 Estimate of bias of the primary and secondary standards.
6.5 Calibration Procedure:
6.5.1 Calibrate the heat flow meter apparatus under the same conditions of plate temperatures, temperature gradient, specimen
thickness, heat flow direction, and apparatus orientation as those for which data are available for the standard.
6.5.2 Single Temperature Point—If the calibration standard is tested at a single mean temperature, conduct the calibration and
subsequent tests near the same mean temperature. Use engineering judgment or an error analysis to determine how closely the
mean temperature must be maintained. As assessment of the sensitivity of the calibration standard to test conditions should be
determined by the user of the transfer standard to determine its limitations of use.
6.5.3 Multiple Temperature Points—If the calibration standard is tested at three or more mean temperatures, calibrate the heat flow
meter apparatus at the same temperatures using the same temperature gradients (8). A smooth curve can be fitted to the points such
that a calibration factor can be interpolated for any given mean temperature. It is not permissible to extrapolate above or below
the mean temperature range of the calibration standard measurements. Changing the plate temperature of a heat flow meter
apparatus has the potential of changing apparatus calibration. When changing plate temperatures, take steps to determine if the heat
flux transducer calibration factor has changed.
6.5.4 Single Thickness Point—If the original calibration standard is tested at only one thickness, the heat flow meter apparatus can
be calibrated for that thickness without an exhaustive thickness study. If tests are to be conducted at thicknesses other than the
calibrated thickness, make a thorough study of the error of the heat flow meter apparatus at other thicknesses. Several references
on this subject are listed at the end of this test method (4, 7, 8-7-1012, 13, 14).
6.5.5 Multiple Thickness Points—If the original standard is tested at three or more thicknesses, the heat flow meter apparatus can
be calibrated over the same thickness range. A smooth curve can be fitted to the points such that a calibration factor can be
interpolated for any given thickness. If tests are to be conducted at thicknesses above or below the calibrated thicknesses, make
a thorough study of the error of the heat flow meter apparatus at these thicknesses.
6.6 Calibration of Various Designs:
6.6.1 There are several configurations of heat flow meter apparatuses that use one or two heat flux transducers and one or two
specimens in the apparatus. While it is not practical to list all of the possible combinations of apparatus and specimen
configurations, this section contains the equations for calculating the calibration factor of three common apparatuses. The
calibration and testing configuration should be identical. The calibration factor of a heat flow meter apparatus is determined by
running the same standard specimens a number of times, not consecutively, but over a period of time with the standard removed
each time.
6.6.2 One Calibration Standard—Apparatus with one heat flux transducer and one standard (see Fig. 1).
S 5 C· Th 2 Tc /E (1)
~ !
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6.6.3 Two Calibration Standards—Apparatus with one heat flux transducer and one specimen configuration (same as that for
6.6.2).
6.6.3.1 The two calibration standards need to be the same thickness and of similar material but need not be identical. With the
following equation, it is not necessary to know the thermal conductance of each calibration standard, but it is necessary to know
the average thermal conductance of the two standards:
C 1C
a b
S 5 (2)
E E
a b
S D
~T 2 T ! ~T 2 T !
ha ca hb cb
6.6.3.2 Two Calibration Standards—Apparatus with one heat flux transducer and two specimens (see Fig. 2).
6.6.3.3 Again, the standards need to be the same thickness and of similar material but not necessarily identical.
C 1C
a b
S 5 (3)
1 1
E· 1
S D
~T 2 T ! ~T 2 T !
ha ca hb cb
6.6.4 One Calibration Standard—Apparatus with two heat flux transducers and one specimen (see Fig. 3).
6.6.4.1 Assuming the two transducers physically are identical and have similar outputs, one can sum the outputs of the two
transducers and then calibrate as a single transducer apparatus. In this case, it is very important to keep the mean temperature and
the plate temperatures equal to those used in testing the standard. It is essential that each of the transducers be at steady state.
C· Th 2 Tc
~ !
S 5 (4)
~E11E2!
6.6.4.2 In the case where multiple transducers are used, a similar calculation can be utilized to calculate the calibration factor.
6.6.4.3 As an alternative, each heat flux transducer can be calibrated as an independent apparatus as in 6.6.1.
7. Test Procedures
7.1 Foreword on Testing Procedures—The relative simplicity of this test method may lead one to overlook very important factors,
which may affect the results. To ensure accurate measurement, the operator shall be instructed fully in the operation of the
equipment. Furthermore, the equipment shall be calibrated properly with reference materials having similar heat transfer
characteristics. Also it is necessary that the specimen be prepared properly for evaluation.
7.2 Sampling and Preparation of Specimens:
7.2.1 Test Specimens—One- or two-piece specimens may be used, depending on the configuration selected for the test. Where two
pieces are used, they shall be selected from the same material to be essentially identical in construction, thickness, and density.
For loose fill materials, the method specified in the material specification or in Practice C687 shall be used to produce a specimen
or specimens of the desired density.
7.2.2 Selection of Specimens—The specimen or specimens shall be of such size as to cover the plate assembly surfaces and shall
either be of the actual thickness to be applied in use or of sufficient thickness to give a true average representation of the material
to be tested. If sufficient material is not available, the specimen shall at least cover the metering area, and the rest of the plate
surfaces must be covered with a mask with a thermal conductivity as close to that of the specimen as possible.
7.3 Specimen Conditioning—Details of the specimen selection and conditioning preferably are given in the material specification.
Where such specifications are not given, the specimen preparation shall be conducted in accordance with the requirement that
materials shall not be exposed to temperatures that will change the specimens in an irreversible manner. Typically, the material
specifications call for specimen conditioning at 22°C and 50 % R.H. for a period of time until less than a 1 % mass change is
observed over a 24-h period. For some materials, such as cellulose, considerably longer times may be required for both
conditioning and testing.
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7.4 Specimen Preparation:
7.4.1 Use the following guidelines when the material specification is unavailable. In general, the surfaces of the specimen should
be prepared to ensure that they are parallel with and have uniform thermal contact with the hot and cold plates.
7.4.2 Compressible Specimens—The surfaces of the uncompressed specimens may be comparatively uneven so long as surface
undulations are removed under test compression. It may be necessary to smooth the specimen surfaces to achieve better
plate-to-specimen contact. If the apparent thermal conductivity of the contact void is greater than that of the specimen,
compressible or otherwise, the measured heat flux will be greater than the heat flux that would be obtained if the voids were absent.
This may often be the case at higher temperatures where radiant heat transfer predominates in the void. For the measurement of
compressible specimens, the temperature sensors are often mounted directly in the plate surfaces. Also, plate spacers may be
required for the measurement of compressible specimens.
7.4.3 Rigid and High Conductance Specimens—The measurement of rigid specimens or high conductance specimens requires
careful surface preparation. First, the surfaces should be made flat and parallel to the same degree as the heat-flow-meter. If the
specimen has a thermal resistance that is sufficiently high compared to the specimen-to-plate interface resistance, temperature
sensors mounted in the plates may be adequate.
7.5 Measurements on Specimens:
7.5.1 Blanket and Batt-Type Materials—When specified, the test thickness of blankets and batt-type materials shall be determined
before testing in accordance with Test Methods C167, provided that good contact is maintained between the specimen and the
isothermal plates. Also, it is recommended highly that the thickness during the actual test be measured. At the conclusion of the
test, the density in the metering area should be determined.
7.5.2 Loose-fill Materials—These materials generally are tested in open test frames as spelled out in Practice C687. The
requirement to measure the density in the metering area is again critical.
7.6 Limitations on Specimen Thickness:
7.6.1 General—The combined thickness of the specimen or specimens, the heat flux transducer and any damping material, which
in total equals the distance between the cold and hot plates, must be restricted in order to limit the effect of edge losses on the
measurements. In addition edge losses are affected by the edge insulation and the ambient temperature, so the requirements on both
of these parameters must be met.
7.6.2 Maximum Spacing Between Hot and Cold Plates—The maximum allowable distance between the hot and cold plates during
a test, is related to the dimensions of the heat flux transducer, the metering area, the size of the plate assembly, the construction
of the heat meter apparatus, and the properties of the specimen. No suitable theoretical analysis is available to predict the maximum
allowable thickness of specimens. It is possible to use the results of an analysis for a similarly sized guarded hot plate as a guide
(15, 16-11-1714).
7.7 Procedure of Measurement:
7.7.1 Temperature Difference—For any test, make the temperature difference across the specimen not less than 10 K. For
specimens that are expected to have a large thermal resistance, a larger temperature difference in the specimen is recommended
(see Practice C1058 for the selection of the plate temperatures). The actual temperature difference or gradient is best specified in
the material specifications or by agreement of the parties concerned.
7.7.2 Edge Insulation—Enclose the edges of the specimens with thermal insulation to reduce edge heat losses to an acceptable
level if this edge insulation is not built into the apparatus (see A1.6).
7.7.3 Settling Time and Measurement Interval—Verify the existence of thermal equilibrium by observing and recording, the emf
output of the heat flux transducer, the mean temperature of the specimens, the temperature drop across the specimen, and a
calculated λ value. Make observations at time intervals of at least 10 min until five successive observations yield values of thermal
conductivity, which fall within ⁄2 % of the mean value for these five readings. If the five readings show a monotonically increasing
or decreasing trend, equilibrium has not been attained. In this case, additional sets of readings shall be taken. If experience has
C518 − 21
shown that a shorter time interval may be used, follow the same criteria for stability. For high density specimens (ρ > 40 kg/m )
or for low conductance specimens (C < 0.05 W/K·m ) the time between readings may have to be increased to 30 min or longer
(1815).
8. Calculation
8.1 Density and Change in Mass—When required, calculate the density of the dry specimen as tested, ρ, the mass change due to
conditioning of the material, and the mass change of the specimen during test.
8.1.1 Density of Batt and Blanket Specimens—It has been found that it is important to measure the mass of the specimens in
contact with the metering area. The area of the specimen directly measured shall be cut out and its mass determined after testing,
unless the specimen must be retained for further testing.
8.2 Thermal Properties for One Specimen—When only one specimen is used, calculate the thermal conductance of the specimen
as follows:
C 5 S·E/ΔT (5)
and where applicable, calculate the thermal conductivity, as follows:
λ5 S·E·~L/ΔT! (6)
8.3 Thermal Properties for Two Specimens—When two specimens are used, calculate the total thermal conductance, C, as follows:
C 5 S·E/ ΔT 1ΔT (7)
~ !
a b
The λ factor, that is, the average thermal conductivity of the specimen is calculated as follows:
λ 5 ~S·E/2!·~L 1L !/~ΔT 1ΔT ! (8)
ave a b a b
where the subscripts refer to the two specimens.
8.4 Other derived thermal properties may be calculated but only under the provisions given in Practice C1045.
8.5 Thermal Properties for Two Transducers—All pertinent equations of 8.2 and 8.3 apply to this configuration, provided S·E will
be replaced by (S’·E’ + S”·E”)/2, where the superscripts ’ and ” refer to the first and second heat flux transducer, respectively.
9. Report
9.1 The report of the results of each test shall include the following information with all data to be reported in both SI and
inch-pound units unless specified otherwise.
9.1.1 The report shall be identified with a unique numbering system to allow traceability back to the individual measurements
taken during the test performed.
9.1.2 Name and any other pertinent identification of the material including a physical description.
9.1.3 Description of the specimen and its relationship to the sample, including a brief history of the specimen, if known.
9.1.4 Thickness of the specimen as received and as tested.
9.1.5 Method and environment used for conditioning, if used.
9.1.6 Density of the conditioned specimen as tested, kg/m .
9.1.7 Mass loss of the specimen during conditioning and testing, in percentage of conditioned mass, if measured.
9.1.8 Mass regain of the specimen during test, in percentage of conditioned mass, if measured.
9.1.9 Average temperature gradient in the specimen during test as computed from the temperatures of the hot and cold surfaces,
K/m.
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9.1.10 Mean temperature of the test, K or °C.
9.1.11 Heat flux amount and direction through the specimen, W/m .
9.1.12 Thermal conductance, W/m · K.
9.1.13 Duration of the measurement portion of the test, min or h.
9.1.14 For loose-fill materials, report the specimen preparation followed.
9.1.15 Date of test, the date of the last heat meter calibration, and the type or types of materials used.
9.1.16 Estimated or calculated uncertainty in reported values. It is optional as to which of the error analysis methods given in
Annex A2 is used by the laboratory.
9.1.17 Orientation and position of the heat meter apparatus during test (vertical, horizontal, etc.), and whether the meter was
against the hot or cold surface of the specimen and whether the edges of the specimen(s) were sealed or open to the ambient.
9.1.18 For direct reading apparatus, the results of the calibration of electronic circuitry and equipment or a statement of
compliance including date, and a statement of compliance on linearity requirements.
9.2 In many cases a laboratory is requested to provide only the thermal conductivity at a specified mean temperature and a few
pertinent physical properties, such as density, and test thickness. An abridged test report shall state “Abridged ASTM C518 Test
Report” and shall include the thermal transmission property of interest, mean temperature, test thickness, and bulk density. It is
mandated that an uncertainty statement shall be transmitted with the thermal transmission property. Compliance to Test Method
C518 requires that the other test parameters specified in 9.1.1 – 9.4 to be recorded in the laboratory records.
9.3 For certification testing only, the specimens used in calibration shall be identified as to the type, thermal resistance, date of
specimen certification, source of certification, expiration date of calibration, and the certification test number. Where applicable
include a statement of the laboratory accreditation of the test facility, including the date of the latest inspection.
9.4 Statement of compliance, or where circumstances or requirements preclude complete compliance with the procedures of the
test, agreed exceptions. A suggested wording is “This test conformed with all requirements of ASTM C518– with with the
exception of (a complete list of exceptions follows).”
10. Precision and Bias
10.1 This section on precision and bias for heat flow meter apparatus includes a discussion of; general statistical terms; statistical
control; factors affecting test results; ruggedness tests; interlaboratory comparisons conducted by ASTM Committee C16;
proficiency testing conducted under the auspices of the National Voluntary Laboratory Accreditation Program (NVLAP); and error
propagation formulae.
10.2 The accuracy of a test result refers to the closeness of agreement between the observed value and an accepted reference value.
When applied to a set of observed values, the accuracy includes a random component (imprecision) and a systematic component
(bias). The variability associated with the set of observed values is an indication of the uncertainty of the test result. Additional
information on statistical terminology is available in Terminology .
10.3 The user of the heat-flow-meter apparatus shall demonstrate that the apparatus is capable of performing in a consistent
manner over time (1916, 2017). The use of control charts (see Manual 7 (2118)) to monitor the operation of the heat-flow-meter
is one recommended way to monitor the control stability of the apparatus. When possible, it is recommended that a reference
material traceable to a national standards laboratory be used as the control specimen. Ideally, the long-term variation should be no
greater than the short-term variability.
10.4 A series of three round robins was conducted between 1976 and 1983, as reported by Hust and Pelanne (2219), and employed
low density fiberglass specimens from 2.54 to 10.2 cm. thick with densities ranging from 10 to 33 kg/m . A total of twelve
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laboratories were involved in these studies. The interlaboratory imprecision, at the two standard deviation level when analyzed
using Practice E691, was found to vary from 1.92 to 3.54 % between 2.54 and 10.2 cm.
10.5 A round robin conducted in 1987, as reported by Adams and Hust, included eleven participating laboratories testing a
fiberglass blanket and several types of loose-fill insulations (2320). The blanket insulation had an interlaboratory imprecision of
3.7 % at the two standard deviation level. The loose-fill interlaboratory imprecision was found to be > 10 % for different materials
at the two standard deviation level. It has been suggested that the principal cause for the significant differences observed is the
various specimen preparation techniques used by the various laboratories.
10.6 A round robin conducted in 1990, as reported by McCaa and Smith, et. al., included ten participating laboratories testing a
fiberglass blanket and several type of loose-fill insulation (2421). The blanket insulation had an interlaboratory imprecision of
2.8 % at the two standard deviation level. The loose-fill interlaboratory imprecision was found to be 5.0 % for perlite, 5.8 % for
cellulose, 9.4 % for unbonded fiberglass, and 10.5 % for mineral wool at the two standard deviation level. This represented a
significant improvement over the 1987 results and is attributed to a more concise specimen preparation procedure in Practice C687.
10.7 An Interlaboratory “Pilot Run” of Small Heat-Flow-Meter Apparatus for ASTM C518 was reported in 1999 (2522). A
precision statement was prepared in accordance with Practice E691. The precision statement is provisional because an insufficient
number of materials were involved. Within 5 years additional data will be obtained and processed that meet the requirements of
Practice E691. A bias statement was prepared following Test Method C177. Bias as compared to results from the Test Method C177
apparatus was found to be statistically insignificant at the α = 5 % level (95 % confidence interval) for the materials studied.
10.8 Proficiency Tests—Interlaboratory testing carried out between nine laboratories under the National Voluntary Laboratory
Accreditation Program currently is showing an interlaboratory imprecision of 2.12 % at the two standard deviation level based on
testing of similar but not identical specimens (2623, 2724).
10.9 An interlaboratory study was performed in 2002-2004. A total of thirteen laboratories participated in the study, testing two
specimens for both thickness and thermal resistivity. Two 25 mm thick expanded polystyrene (EPS) foam board specimen (A and
B) of similar thickness and thermal performance were used for this study. Each test result was to be repeated for a total of two
determinations. The precision and bias statements were determined through statistical examination of two individual results, from
the participating laboratories, on two samples. The results are shown in Table 1 and Table 2.
11. Keywords
11.1 calibration; error analysis; heat flow meter apparatus, thermal resistance; heat flux; instrument verification; thermal
conductivity; thermal testing
TABLE 1 Summary of Precision Statistics for Thermal Resistivity Reproducibility
Reproducibility
Reproducibility
A
Average Standard
B
Material
Limit
A
(m K / W)
Deviation
(m K / W)
(m K / W)
x¯ S R
R
A (n=13) 29.76 0.31 0.88
2.94 %
B (n=13) 30.02 0.27 0.75
2.50 %
A
Calculated from all reporting laboratories (n=13 for materials A & B).
B
95 % reproducibility limit is 2.8 times the reproducibility standard deviation (between laboratory).
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:C16-1047. Contact ASTM Customer
Service at [e-mail].
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TABLE 2 Summary of Precision Statistics for Thermal Resistivity Repeatability
Repeatability
Repeatability
A
Average Standard
B
Material
Limit
A
(m K / W)
Deviation
(m K / W)
(m K / W)
x¯ S r
r
A (n=10) 29.73 0.18 0.50
1.68 %
B (n=8) 29.99 0.15 0.41
1.37 %
A
Calculated from all reporting laboratories (n=10 for material A, n=8 for material B).
B
95 % repeatability limit is 2.8 times the repeatability standard deviation (within laboratory).
ANNEXES
(Mandatory Information)
A1. EQUIPMENT DESIGN
A1.1 The exposed surfaces of the plates and the heat flux transducer, that is, the surfaces making contact with the specimens, shall
be painted or otherwise treated to have a total hemispherical emittance of greater than 0.8 at their operating temperatures (see Note
A1.1).
NOTE A1.1—Hard anodizing of aluminum produces a surface with a total hemispherical emittance of approximately 0.85. Several paints are available,
which when applied as directed, produce a total hemispherical emittance of approximately 0.86.
A1.2 Plate Assemblies, Hot and Cold—The two plate assemblies should provide isothermal surfaces in contact with either side
of the test specimen. The assemblies consist of heat source or sink, a high conductivity surface, means to measure surface
temperature, and means of support. A heat flux transducer may be attached to one, both, or neither plate assembly, depending upon
the design, (see Section 6). In all cases, the area defined by the sensor of the heat flux transducer is called the metering area and
the remainder of the plate is the guard area.
A1.2.1 A means shall be provided to maintain the temperature of the plate assemblies at the desired level. Examples are fluid
baths, electrical heaters, or thermoelectric coolers, or a combination thereof (28-25-3027).
A1.2.2 If a heat flux transducer is located at the midplane of the specimens (see Fig. 2),
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