ASTM C1130-24

Standard Practice for Calibration of Thin Heat Flux Transducers

SIGNIFICANCE AND USE
5.1 The application of HFTs and temperature sensors to building envelopes provide in-situ data for evaluating the thermal performance of an opaque building envelope component under actual environmental conditions, as described in Practices C1046 and C1155. These applications require calibration of the HFTs at levels of heat flux and temperature consistent with end-use conditions.  
5.2 This practice provides calibration procedures for the determination of the heat flux transducer sensitivity, S, that relates the HFT voltage output, E, to a known input value of heat flux, q.  
5.2.1 The applied heat flux, q, shall be obtained from steady-state tests conducted in accordance with either Test Method C177, C518, C1114, C1363, or, for cryogenic applications, Guide C1774.  
5.2.2 The resulting voltage output, E, of the heat flux transducer is measured directly using (auxiliary) readout instrumentation connected to the electrical output leads of the sensor.
Note 1: A heat flux transducer (see also Terminology C168) is a thin stable substrate having a low mass in which a temperature difference across the thickness of the device is measured with thermocouples connected electrically in series (that is, a thermopile). Commercial HFTs typically have a central sensing region, a surrounding guard, and an integral temperature sensor that are contained in a thin durable enclosure. Practice C1046, Appendix X2 includes detailed descriptions of the internal constructions of two types of HFTs.  
5.3 The HFT sensitivity depends on several factors including, but not limited to, size, thickness, construction, temperature, applied heat flux, and application conditions including adjacent material characteristics and environmental effects.  
5.4 The subsequent conversion of the HFT voltage output to heat flux under application conditions requires (1) a standardized technique for determining the HFT sensitivity for the application of interest; and, (2) a comprehensive understanding of t...
SCOPE
1.1 This practice, in conjunction with either Test Method C177, C518, C1114, or C1363, establishes procedures for the calibration of heat flux transducers that are dimensionally thin in comparison to their planar dimensions.  
1.1.1 The thickness of the heat flux transducer shall be less than 30 % of the narrowest planar dimension of the heat flux transducer.  
1.2 This practice describes techniques for determining the sensitivity, S, of a heat flux transducer when subjected to one dimensional heat flow normal to the planar surface or when installed in a building application.  
1.3 This practice shall be used in conjunction with Practice C1046 and Practice C1155 when performing in-situ measurements of heat flux on opaque building envelope components. This practice is comparable, but not identical, to the calibration techniques described in ISO 9869-1.  
1.4 This practice is not intended to determine the sensitivity of heat flux transducers used as components of heat flow meter apparatus, as in Test Method C518, or used for in-situ industrial applications, as covered in Practice C1041.  
1.5 This practice does not preclude the laboratory calibration of heat flux transducers for large-scale insulation systems operated at temperatures lower or higher than that for building envelope components. For these applications, the heat flux transducers shall be calibrated at the temperatures that the transducer will be used.  
1.5.1 For cryogenic applications, the test apparatuses described in Guide C1774 are acceptable methods for calibration.  
1.6 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.  
1.7 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered sta...

General Information

• Status: Published
• Publication Date: 14-Mar-2024
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.30 - Thermal Measurement

Relations

• Replaces: ASTM C1130-21 - Standard Practice for Calibration of Thin Heat Flux Transducers
• Effective Date: 15-Mar-2024
• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM C1774-24 - Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems
• Effective Date: 15-Mar-2024
• Refers: ASTM C1044-24 - Standard Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
• Effective Date: 01-Mar-2024
• Refers: ASTM C168-22 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-May-2022
• Refers: ASTM C1044-16(2020) - Standard Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
• Effective Date: 01-Oct-2020
• Refers: ASTM C1774-13(2019) - Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems
• Effective Date: 01-Sep-2019
• Refers: ASTM C1363-19 - Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
• Effective Date: 01-Sep-2019
• Referred By: ASTM C1363-24 - Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
• Effective Date: 15-Mar-2024
• Referred By: ASTM E2684-17 - Standard Test Method for Measuring Heat Flux Using Surface-Mounted One-Dimensional Flat Gages
• Effective Date: 15-Mar-2024
• Referred By: ASTM C1470-20 - Standard Guide for Testing the Thermal Properties of Advanced Ceramics
• Effective Date: 15-Mar-2024
• Referred By: ASTM C1155-95(2021) - Standard Practice for Determining Thermal Resistance of Building Envelope Components from the In-Situ Data
• Effective Date: 15-Mar-2024
• Referred By: ASTM C1046-95(2021) - Standard Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components
• Effective Date: 15-Mar-2024

Overview

ASTM C1130-24 is the standard practice developed by ASTM International for the calibration of thin heat flux transducers (HFTs). These precision sensors are instrumental in measuring heat flux and thermal performance, particularly for opaque building envelope components. Accurate calibration of HFTs is crucial for generating reliable in-situ data under real-life environmental conditions, supporting energy performance assessments and research for building envelopes.

This standard establishes detailed procedures for determining the sensitivity of thin HFTs. Calibration ensures that the voltage output from the transducer can be directly and accurately related to a known input value of heat flux, enabling effective energy efficiency analysis and thermal resistance calculations.

Key Topics

• Calibration Techniques: ASTM C1130-24 outlines three primary calibration methods for thin HFTs:

  • Ideally-guarded: Utilizes a homogeneous, thermally characterized test stack to ensure one-dimensional heat flow.
  • Embedded: Places the HFT within stack layers that mimic the intended building application.
  • Surface-mounted: Involves mounting the HFT on the surface of a test panel to replicate field conditions.

• Determination of Sensitivity: Sensitivity, the ratio of electrical output to heat flux through the device, is rigorously tested using steady-state methods. This ensures precise conversion of electrical readings to actual heat flux measurements.

• Factors Affecting Calibration: The standard acknowledges that sensitivity may vary due to transducer size, thickness, construction, application temperatures, applied heat flux, and environmental factors.

• Integration with Other Standards: Calibration under this practice is performed using established ASTM methods such as C177, C518, C1114, and C1363. For specialized (e.g., cryogenic) applications, Guide C1774 is used.

• Reporting and Uncertainty: ASTM C1130-24 requires comprehensive reporting of calibration data, including HFT details, calibration approach, test conditions, and uncertainty analysis per current international guidelines.

Applications

Practical applications of ASTM C1130-24 include:

• Building Envelope Assessment: Calibrated HFTs enable accurate measurement and monitoring of heat flow through walls, roofs, and other opaque components in buildings, a key element in thermal performance evaluation.
• Energy Efficiency Studies: Reliable HFT calibration supports effective analysis of a structure’s thermal resistance (R-value) and can inform retrofit decisions, compliance, and performance verification.
• Research and Product Development: Manufacturers and researchers use calibrated transducers for product testing, material characterization, and advanced building science research.
• Special Environments: The standard accommodates calibration for both standard and extreme scenarios, including high-temperature and cryogenic environments, ensuring flexible application.

Related Standards

ASTM C1130-24 is designed to be used with several related ASTM and ISO standards, which provide methods and terminology to support its application:

• ASTM C1046: Practice for in-situ measurement of heat flux and temperature on building envelope components.
• ASTM C1155: Practice for determining thermal resistance of building envelope components from in-situ data.
• ASTM C177, C518, C1114, C1363: Test methods for measuring steady-state thermal transmission and thermal performance of materials and building assemblies.
• ASTM C168: Standard for terminology related to thermal insulation.
• ASTM C1774: Guide for thermal performance testing of cryogenic insulation systems.
• ISO 9869-1: International standard for in-situ measurement of thermal resistance and transmittance for building elements.

Summary of Value

Implementing ASTM C1130-24 ensures that thin heat flux transducers are accurately calibrated for their intended use, supporting precise measurement of thermal performance in buildings. This has direct value for contractors, building scientists, manufacturers, and regulatory agencies aiming to improve energy efficiency and ensure compliance with thermal standards for building envelopes. Consistent, reliable calibration leads to better data, supporting sustainability initiatives and performance benchmarking in the built environment.

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: C1130 − 24
Standard Practice for
Calibration of Thin Heat Flux Transducers
This standard is issued under the fixed designation C1130; 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.
1. Scope 1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice, in conjunction with either Test Method
responsibility of the user of this standard to establish appro-
C177, C518, C1114, or C1363, establishes procedures for the
priate safety, health, and environmental practices and deter-
calibration of heat flux transducers that are dimensionally thin
mine the applicability of regulatory limitations prior to use.
in comparison to their planar dimensions.
1.9 This international standard was developed in accor-
1.1.1 The thickness of the heat flux transducer shall be less
dance with internationally recognized principles on standard-
than 30 % of the narrowest planar dimension of the heat flux
ization established in the Decision on Principles for the
transducer.
Development of International Standards, Guides and Recom-
1.2 This practice describes techniques for determining the
mendations issued by the World Trade Organization Technical
sensitivity, S, of a heat flux transducer when subjected to one
Barriers to Trade (TBT) Committee.
dimensional heat flow normal to the planar surface or when
installed in a building application.
2. Referenced Documents
1.3 This practice shall be used in conjunction with Practice
2.1 ASTM Standards:
C1046 and Practice C1155 when performing in-situ measure-
C168 Terminology Relating to Thermal Insulation
ments of heat flux on opaque building envelope components.
C177 Test Method for Steady-State Heat Flux Measure-
This practice is comparable, but not identical, to the calibration
ments and Thermal Transmission Properties by Means of
techniques described in ISO 9869-1.
the Guarded-Hot-Plate Apparatus
1.4 This practice is not intended to determine the sensitivity
C518 Test Method for Steady-State Thermal Transmission
of heat flux transducers used as components of heat flow meter
Properties by Means of the Heat Flow Meter Apparatus
apparatus, as in Test Method C518, or used for in-situ
C1041 Practice for In-Situ Measurements of Heat Flux in
industrial applications, as covered in Practice C1041.
Industrial Thermal Insulation Using Heat Flux Transduc-
1.5 This practice does not preclude the laboratory calibra-
ers (Withdrawn 2019)
tion of heat flux transducers for large-scale insulation systems
C1044 Practice for Using a Guarded-Hot-Plate Apparatus or
operated at temperatures lower or higher than that for building
Thin-Heater Apparatus in the Single-Sided Mode
envelope components. For these applications, the heat flux
C1046 Practice for In-Situ Measurement of Heat Flux and
transducers shall be calibrated at the temperatures that the
Temperature on Building Envelope Components
transducer will be used.
C1114 Test Method for Steady-State Thermal Transmission
1.5.1 For cryogenic applications, the test apparatuses de-
Properties by Means of the Thin-Heater Apparatus
scribed in Guide C1774 are acceptable methods for calibration.
C1155 Practice for Determining Thermal Resistance of
Building Envelope Components from the In-Situ Data
1.6 The text of this standard references notes and footnotes
C1363 Test Method for Thermal Performance of Building
which provide explanatory material. These notes and footnotes
Materials and Envelope Assemblies by Means of a Hot
(excluding those in tables and figures) shall not be considered
Box Apparatus
as requirements of the standard.
C1774 Guide for Thermal Performance Testing of Cryogenic
1.7 Units—The values stated in SI units are to be regarded
Insulation Systems
as standard. The values given in parentheses are provided for
information only and are not considered standard.
1 2
This practice is under the jurisdiction of ASTM Committee C16 on Thermal For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Measurement. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved March 15, 2024. Published March 2024. Originally the ASTM website.
approved in 1989. Last previous edition approved in 2021 as C1130 – 21. DOI: The last approved version of this historical standard is referenced on
10.1520/C1130-24. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1130 − 24
2.2 ISO Standards: and incorporates environmental effects that cause lateral heat
ISO 9869-1 Thermal insulation – Building elements – In-situ flow in the locality of the HFT.
measurement of thermal resistance and thermal transmit-
4.2 The calibration results are intended for use with Practice
tance – Part 1: Heat flow meter method
C1046 to measure in-situ the heat flux through opaque building
envelope components and with Practice C1155 for the subse-
3. Terminology
quent analysis of the measurement data. The intended applica-
3.1 Definitions—For definitions of terms relating to thermal
tion of the HFT is used to determine the appropriate calibration
insulating materials, see Terminology C168.
technique (2).
3.2 Definitions of Terms Specific to This Standard: 4.2.1 If the HFT is to be embedded in the building envelope,
3.2.1 mask—material (or materials) having the same, or the HFT shall be calibrated in a test stack of materials that
nearly the same, thermal properties and thickness surrounding simulate the surrounding construction materials.
the heat flux transducer thereby promoting one-dimensional 4.2.2 If the HFT is to be surface mounted on the building
heat flow through the heat flux transducer.
envelope construction, the HFT shall be calibrated using a hot
box that is oriented similarly (horizontal, vertical, or inclined)
3.2.2 R-squared (R )—coefficient of determination (also
as the measurement site.
known as “goodness of fit”) is a statistical measure of how
close the data are to the fitted line.
5. Significance and Use
3.2.3 sensitivity—the ratio of the electrical output of the heat
flux transducer to the heat flux passing through the device 5.1 The application of HFTs and temperature sensors to
when measured under steady-state heat flow. building envelopes provide in-situ data for evaluating the
thermal performance of an opaque building envelope compo-
3.2.4 test stack—a layer or a series of layers of material put
nent under actual environmental conditions, as described in
together to comprise a test sample (for example, a roof system
Practices C1046 and C1155. These applications require cali-
containing a membrane, an insulation, and a roof deck).
bration of the HFTs at levels of heat flux and temperature
3.3 Symbols:
consistent with end-use conditions.
3.3.1 E—measured HFT output voltage, V.
5.2 This practice provides calibration procedures for the
2 2
3.3.2 q—steady-state heat flux, W/m (Btu/h·ft ).
determination of the heat flux transducer sensitivity, S, that
2 2
3.3.3 S—sensitivity, V/(W/m ) (V/(Btu/h·ft )).
relates the HFT voltage output, E, to a known input value of
3.3.4 u —combined standard uncertainty, V. heat flux, q.
c
5.2.1 The applied heat flux, q, shall be obtained from
3.3.5 u —standard uncertainty of the regression coefficients,
steady-state tests conducted in accordance with either Test
V.
Method C177, C518, C1114, C1363, or, for cryogenic
3.3.6 u —standard uncertainty for replicate measurements,
applications, Guide C1774.
V.
5.2.2 The resulting voltage output, E, of the heat flux
3.3.7 u —standard uncertainty for the measurement, V.
transducer is measured directly using (auxiliary) readout in-
strumentation connected to the electrical output leads of the
4. Summary of Practice
sensor.
4.1 This practice presents three techniques for the labora-
NOTE 1—A heat flux transducer (see also Terminology C168) is a thin
tory calibration of heat flux transducers (1) : (1) ideally
stable substrate having a low mass in which a temperature difference
guarded; (2) embedded; and, (3) surface mounted. These
across the thickness of the device is measured with thermocouples
techniques establish a hierarchy defined by the extent that the
connected electrically in series (that is, a thermopile). Commercial HFTs
assumption of one-dimensional heat flow is satisfied (1).
typically have a central sensing region, a surrounding guard, and an
integral temperature sensor that are contained in a thin durable enclosure.
4.1.1 The ideally-guarded technique places the heat flux
Practice C1046, Appendix X2 includes detailed descriptions of the
transducer (HFT) in a test stack consisting of homogeneous,
internal constructions of two types of HFTs.
thermally characterized materials that promotes one-
5.3 The HFT sensitivity depends on several factors
dimensional heat flow normal to the planar dimensions of the
including, but not limited to, size, thickness, construction,
HFT. The results of this technique provide a baseline calibra-
temperature, applied heat flux, and application conditions
tion for the HFT.
including adjacent material characteristics and environmental
4.1.2 The embedded technique places the HFT within a test
effects.
stack consisting of material layers identical, or comparable to,
the building construction to be studied under application.
5.4 The subsequent conversion of the HFT voltage output to
4.1.3 The surface mounted calibration, which is the most
heat flux under application conditions requires (1) a standard-
complex, places the HFT on the external surface of a test stack
ized technique for determining the HFT sensitivity for the
application of interest; and, (2) a comprehensive understanding
4 of the factors affecting its output as described in Practice
Available from International Organization for Standardization (ISO), ISO
C1046.
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org.
5.5 The installation of a HFT potentially changes the local
The boldface numbers in parentheses refer to the references at the end of this
standard. thermal resistance of the test artifact and the resulting heat flow
C1130 − 24
differs from that for the undisturbed building envelope com- 6.1.3 Surface-Mounted—Place the HFT and temperature
ponent. The following techniques have been used to compen- sensor in the central location of the metered area of the hot box
sate for this effect. (Test Method C1363).
5.5.1 Ensure that the installation is adequately guarded (3). 6.1.4 Sensor Leads—The sensor output leads shall be placed
In some cases, an assumption is made that the change in
in grooves or covered to minimize the presence of air gaps in
thermal resistance is negligible, particularly for very thin HFTs the test stack or surface mounted installation. The HFT need
with a large surrounding guard, or is incalculable (1).
not be physically adhered to the mask or embedding material.
5.5.2 For the embedded configuration, analytical and nu- Thermally conductive gel or paste is applied, if necessary, to
merical methods have been used to account for the disturbance
one or both faces of the heat flux transducer to improve the
of the heat flux due to the presence of the HFT. Such analyses thermal contact.
are outside the scope of this practice but details are available in
6.2 Ideally Guarded Configuration (One-dimensional Heat
Refs (4-8).
Flow):
5.5.3 For the surface-mounted configuration, measurement
6.2.1 Refer to Fig. 1 for an illustration of the ideally-
errors have been quantified by Trethowen (9). Empirical
guarded stack configuration.
calibrations have also been determined by conducting a series
6.2.2 Calibration of One HFT—Place the HFT and tempera-
of field calibrations or measurements. Such procedures are
ture sensor in the center of a guard mask have the same
outside the scope of this practice but details are available in
thickness and thermal resistance as the HFT. The outer
Orlandi et al. (10) and Desjarlais and Tye (11).
dimensions of the guard mask shall be the same size as the
5.6 Cryogenic and high temperature calibrations shall con-
apparatus plates. Place the HFT/guard assembly between two
sider the effect of parasitic heat transfer due to large environ-
layers of high-density fibrous glass insulation board or other
mental temperature differences in performing thermal bal-
homogenous semirigid insulating material. It is recommended
ances. The calibration and testing of heat flux transducers at
that the test stack have the smallest acceptable thickness and
cryogenic temperatures using the flat plate boiloff absolute
thermal resistance to minimize edge effects during testing.
calorimeter described in Guide C1774 and an unguarded flat
6.2.3 Calibration of multiple HFTs—To determine the sen-
plate method are described by Johnson et al. (12).
sitivity of multiple small heat flux transducers, replace the
HFT/mask layer shown in Fig. 1 with a layer containing an
6. Specimen Preparation
arrangement of HFTs located within the metered area of the
6.1 Preparation of the HFT, Test Stack, and Surface-
apparatus as illustrated in Fig. 2.
Mounted Installation:
NOTE 2—The plate designs of some apparatus utilize a circular
6.1.1 HFT—Verify the electrical continuity of the HFT and
geometry.
temperature sensor. Where auxiliary readout instrumentation,
6.3 Embedded Configuration:
that is, voltmeter, recorder, or data acquisition system, is
6.3.1 Consult Practice C1046 for details on the installation
needed, the user shall provide appropriate provision for cali-
bration. The instrumentation shall have a resolution capability of the HFT within the building envelope component of interest.
of 2 μV. Construct the test stack to have the same, or comparable,
6.1.2 Test Stack—Place the HFT and temperature sensor in physical properties as the end-use application replicating the
the test stack located within the central metering area of the building construction under evaluation. Place the HFT and
apparatus plates (Test Methods C177, C518, C1114, or Guide temperature sensor within the test stack in the same arrange-
C1774). ment as intended in the end-use application.
FIG. 1 Ideally Guarded Test Configuration for One HFT (Side View)
C1130 − 24
FIG. 2 Calibration of Multiple Small HFTs Evaluated Simultaneously (Top View)
if inside mounting is impossible.
6.3.2 Refer to Fig. 3 for an illustration of an embedded stack
configuration placed between the hot and cold apparatus plates.
6.4.2 It is recommended that a guard mask be placed around
The example in Fig. 3 depicts a case where an HFT is
the HFT to compensate for local heat flux perturbations caused
embedded in gypsum wallboard and faces an insulated wall
by the presence of the HFT. The guard mask shall have the
cavity. It is recommended that, when compressible materials
same emittance as the HFT. Guidance on the determination of
are present, rigid spacer stops or other means be utilized to
the size of the guard mask is available in Burch et al. (3), van
maintain a fixed plate separation during testing.
der Graaf (8), and Trethowen (9).
6.4.3 Refer to Fig. 4 for an illustration of a surface-mounted
6.4 Surface-Mounted Configuration:
configuration calibrated in a hot box (one chamber not shown).
6.4.1 Consult Practice C1046 for details on the installation
The example in Fig. 4 depicts a case where an HFT (guard
of the HFT to the surface of the building envelope component
mask not shown) is affixed to a homogeneous test specimen of
of interest. Attach the HFT and temperature sensor to the
known thermal resistance.
surface of a test panel having the same, or comparable,
physical properties as the building construction under evalua-
7. Procedure
tion replicating the end-use conditions. The test panel shall
have the same orientation (horizontal, vertical, or inclined) as
7.1 Use a guarded-hot-plate, thin-heater, heat-flow-meter, or
the building construction under evaluation.
hot box apparatus to calibrate the HFT/stack assembly and
follow the test procedure of either Test Method C177, C518,
NOTE 3—Trethowen (13) recommends mounting of the HFT on interior
building surfaces. Exterior mounting of the HFT need only be considered C1114, or C1363, respectively.
FIG. 3 Test Stack for an HFT Embedded Within an Insulated Wall Cavity (Side View)
C1130 − 24
FIG. 4 Surface Mounted HFT Configuration (Side View)
7.1.1 For apparatuses that typically require two specimens E
S 5 (1)
follow Practice C1044 for operation of the apparatus in the q
NOTE 5—Practice C1046 uses the terms “calibration factor” or “con-
single-sided mode.
version factor” to denote the conversion of the HFT voltage output to heat
7.1.2 For calibration under cryogenic conditions, utilize the
flux. These terms, which are defined as the multiplicative inverse of the
appropriate apparatus and test procedure described in Guide
HFT sensitivity defined in Eq 1, have the units are (W/m ) per V.
C
...

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: C1130 − 21 C1130 − 24
Standard Practice for
Calibration of Thin Heat Flux Transducers
This standard is issued under the fixed designation C1130; 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.
1. Scope
1.1 This practice, in conjunction with either Test Method C177, C518, C1114, or C1363, establishes procedures for the calibration
of heat flux transducers that are dimensionally thin in comparison to their planar dimensions.
1.1.1 The thickness of the heat flux transducer shall be less than 30 % of the narrowest planar dimension of the heat flux
transducer.
1.2 This practice describes techniques for determining the sensitivity, S, of a heat flux transducer when subjected to one
dimensional heat flow normal to the planar surface or when installed in a building application.
1.3 This practice shall be used in conjunction with Practice C1046 and Practice C1155 when performing in-situ measurements of
heat flux on opaque building envelope components. This practice is comparable, but not identical, to the calibration techniques
described in ISO 9869-1.
1.4 This practice is not intended to determine the sensitivity of heat flux transducers used as components of heat flow meter
apparatus, as in Test Method C518, or used for in-situ industrial applications, as covered in Practice C1041.
1.5 This practice does not preclude the laboratory calibration of heat flux transducers for large-scale insulation systems operated
at temperatures lower or higher than that for building envelope components. For these applications, the heat flux transducers shall
be calibrated at the temperatures that the transducer will be used.
1.5.1 For cryogenic applications, the test apparatuses described in Guide C1774 are acceptable methods for calibration.
1.6 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
1.7 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for
information only and are not considered standard.
1.8 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 establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
This practice 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 Sept. 1, 2021March 15, 2024. Published September 2021March 2024. Originally approved in 1989. Last previous edition approved in 20172021
as C1130 – 17.C1130 – 21. DOI: 10.1520/C1130-21.10.1520/C1130-24.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1130 − 24
1.9 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:
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
C518 Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
C1041 Practice for In-Situ Measurements of Heat Flux in Industrial Thermal Insulation Using Heat Flux Transducers
(Withdrawn 2019)
C1044 Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
C1046 Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components
C1114 Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
C1155 Practice for Determining Thermal Resistance of Building Envelope Components from the In-Situ Data
C1363 Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
C1774 Guide for Thermal Performance Testing of Cryogenic Insulation Systems
2.2 ISO Standards:
ISO 9869-1 Thermal insulation – Building elements – In-situ measurement of thermal resistance and thermal transmittance –
Part 1: Heat flow meter method
3. Terminology
3.1 Definitions—For definitions of terms relating to thermal insulating materials, see Terminology C168.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 mask—material (or materials) having the same, or nearly the same, thermal properties and thickness surrounding the heat
flux transducer thereby promoting one-dimensional heat flow through the heat flux transducer.
3.2.2 R-squared (R )—coefficient of determination (also known as “goodness of fit”) is a statistical measure of how close the data
are to the fitted line.
3.2.3 sensitivity—the ratio of the electrical output of the heat flux transducer to the heat flux passing through the device when
measured under steady-state heat flow.
3.2.4 test stack—a layer or a series of layers of material put together to comprise a test sample (for example, a roof system
containing a membrane, an insulation, and a roof deck).
3.3 Symbols:
3.3.1 E—measured HFT output voltage, V.
2 2
3.3.2 q—steady-state heat flux, W/m (Btu/h·ft ).
2 2
3.3.3 S—sensitivity, V/(W/m ) (V/(Btu/h·ft )).
3.3.4 u —combined standard uncertainty, V.
c
3.3.5 u —standard uncertainty of the regression coefficients, V.
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Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
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3.3.6 u —standard uncertainty for replicate measurements, V.
3.3.7 u —standard uncertainty for the measurement, V.
4. Summary of Practice
4.1 This practice presents three techniques for the laboratory calibration of heat flux transducers (1) : (1) ideally guarded; (2)
embedded; and, (3) surface mounted. These techniques establish a hierarchy defined by the extent that the assumption of
one-dimensional heat flow is satisfied (1).
4.1.1 The ideally-guarded technique places the heat flux transducer (HFT) in a test stack consisting of homogeneous, thermally
characterized materials that promotes one-dimensional heat flow normal to the planar dimensions of the HFT. The results of this
technique provide a baseline calibration for the HFT.
4.1.2 The embedded technique places the HFT within a test stack consisting of material layers identical, or comparable to, the
building construction to be studied under application.
4.1.3 The surface mounted calibration, which is the most complex, places the HFT on the external surface of a test stack and
incorporates environmental effects that cause lateral heat flow in the locality of the HFT.
4.2 The calibration results are intended for use with Practice C1046 to measure in-situ the heat flux through opaque building
envelope components and with Practice C1155 for the subsequent analysis of the measurement data. The intended application of
the HFT is used to determine the appropriate calibration technique (2).
4.2.1 If the HFT is to be embedded in the building envelope, the HFT shall be calibrated in a test stack of materials that simulate
the surrounding construction materials.
4.2.2 If the HFT is to be surface mounted on the building envelope construction, the HFT shall be calibrated using a hot box that
is oriented similarly (horizontal, vertical, or inclined) as the measurement site.
5. Significance and Use
5.1 The application of HFTs and temperature sensors to building envelopes provide in-situ data for evaluating the thermal
performance of an opaque building envelope component under actual environmental conditions, as described in Practices C1046
and C1155. These applications require calibration of the HFTs at levels of heat flux and temperature consistent with end-use
conditions.
5.2 This practice provides calibration procedures for the determination of the heat flux transducer sensitivity, S, that relates the
HFT voltage output, E, to a known input value of heat flux, q.
5.2.1 The applied heat flux, q, shall be obtained from steady-state tests conducted in accordance with either Test Method C177,
C518, C1114, C1363, or, for cryogenic applications, Guide C1774.
5.2.2 The resulting voltage output, E, of the heat flux transducer is measured directly using (auxiliary) readout instrumentation
connected to the electrical output leads of the sensor.
NOTE 1—A heat flux transducer (see also Terminology C168) is a thin stable substrate having a low mass in which a temperature difference across the
thickness of the device is measured with thermocouples connected electrically in series (that is, a thermopile). Commercial HFTs typically have a central
sensing region, a surrounding guard, and an integral temperature sensor that are contained in a thin durable enclosure. Practice C1046, Appendix X2
includes detailed descriptions of the internal constructions of two types of HFTs.
5.3 The HFT sensitivity depends on several factors including, but not limited to, size, thickness, construction, temperature, applied
heat flux, and application conditions including adjacent material characteristics and environmental effects.
The boldface numbers in parentheses refer to the references at the end of this standard.
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5.4 The subsequent conversion of the HFT voltage output to heat flux under application conditions requires (1) a standardized
technique for determining the HFT sensitivity for the application of interest; and, (2) a comprehensive understanding of the factors
affecting its output as described in Practice C1046.
5.5 The installation of a HFT potentially changes the local thermal resistance of the test artifact and the resulting heat flow differs
from that for the undisturbed building envelope component. The following techniques have been used to compensate for this effect.
5.5.1 Ensure that the installation is adequately guarded (3). In some cases, an assumption is made that the change in thermal
resistance is negligible, particularly for very thin HFTs with a large surrounding guard, or is incalculable (1).
5.5.2 For the embedded configuration, analytical and numerical methods have been used to account for the disturbance of the heat
flux due to the presence of the HFT. Such analyses are outside the scope of this practice but details are available in Refs (4-8).
5.5.3 For the surface-mounted configuration, measurement errors have been quantified by Trethowen (9). Empirical calibrations
have also been determined by conducting a series of field calibrations or measurements. Such procedures are outside the scope of
this practice but details are available in Orlandi et al. (10) and Desjarlais and Tye (11).
5.6 Cryogenic and high temperature calibrations shall consider the effect of parasitic heat transfer due to large environmental
temperature differences in performing thermal balances. The calibration and testing of heat flux transducers at cryogenic
temperatures using the flat plate boiloff absolute calorimeter described in Guide C1774 and an unguarded flat plate method are
described by Johnson et al. (12).
6. Specimen Preparation
6.1 Preparation of the HFT, Test Stack, and Surface-Mounted Installation:
6.1.1 HFT—Verify the electrical continuity of the HFT and temperature sensor. Where auxiliary readout instrumentation, that is,
voltmeter, recorder, or data acquisition system, is needed, the user shall provide appropriate provision for calibration. The
instrumentation shall have a resolution capability of 2 μV.
6.1.2 Test Stack—Place the HFT and temperature sensor in the test stack located within the central metering area of the apparatus
plates (Test Methods C177, C518, C1114, or Guide C1774).
6.1.3 Surface-Mounted—Place the HFT and temperature sensor in the central location of the metered area of the hot box (Test
Method C1363).
6.1.4 Sensor Leads—The sensor output leads shall be placed in grooves or covered to minimize the presence of air gaps in the
test stack or surface mounted installation. The HFT need not be physically adhered to the mask or embedding material. Thermally
conductive gel or paste is applied, if necessary, to one or both faces of the heat flux transducer to improve the thermal contact.
6.2 Ideally Guarded Configuration (One-dimensional Heat Flow):
6.2.1 Refer to Fig. 1 for an illustration of the ideally-guarded stack configuration.
6.2.2 Calibration of One HFT—Place the HFT and temperature sensor in the center of a guard mask have the same thickness and
thermal resistance as the HFT. The outer dimensions of the guard mask shall be the same size as the apparatus plates. Place the
HFT/guard assembly between two layers of high-density fibrous glass insulation board or other homogenous semirigid insulating
material. It is recommended that the test stack have the smallest acceptable thickness and thermal resistance to minimize edge
effects during testing.
6.2.3 Calibration of multiple HFTs—To determine the sensitivity of multiple small heat flux transducers, replace the HFT/mask
layer shown in Fig. 1 with a layer containing an arrangement of HFTs located within the metered area of the apparatus as illustrated
in Fig. 2.
NOTE 2—The plate designs of some apparatus utilize a circular geometry.
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FIG. 1 Ideally Guarded Test Configuration for One HFT (Side View)
FIG. 2 Calibration of Multiple Small HFTs Evaluated Simultaneously (Top View)
6.3 Embedded Configuration:
6.3.1 Consult Practice C1046 for details on the installation of the HFT within the building envelope component of interest.
Construct the test stack to have the same, or comparable, physical properties as the end-use application replicating the building
construction under evaluation. Place the HFT and temperature sensor within the test stack in the same arrangement as intended
in the end-use application.
6.3.2 Refer to Fig. 3 for an illustration of an embedded stack configuration placed between the hot and cold apparatus plates. The
example in Fig. 3 depicts a case where an HFT is embedded in gypsum wallboard and faces an insulated wall cavity. It is
recommended that, when compressible materials are present, rigid spacer stops or other means be utilized to maintain a fixed plate
separation during testing.
6.4 Surface-Mounted Configuration:
6.4.1 Consult Practice C1046 for details on the installation of the HFT to the surface of the building envelope component of
interest. Attach the HFT and temperature sensor to the surface of a test panel having the same, or comparable, physical properties
as the building construction under evaluation replicating the end-use conditions. The test panel shall have the same orientation
(horizontal, vertical, or inclined) as the building construction under evaluation.
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FIG. 3 Test Stack for an HFT Embedded Within an Insulated Wall Cavity (Side View)
NOTE 3—Trethowen (13) recommends mounting of the HFT on interior building surfaces. Exterior mounting of the HFT need only be considered if inside
mounting is impossible.
6.4.2 It is recommended that a guard mask be placed around the HFT to compensate for local heat flux perturbations caused by
the presence of the HFT. The guard mask shall have the same emittance as the HFT. Guidance on the determination of the size
of the guard mask is available in Burch et al. (3), van der Graaf (8), and Trethowen (9).
6.4.3 Refer to Fig. 4 for an illustration of a surface-mounted configuration calibrated in a hot box (one chamber not shown). The
example in Fig. 4 depicts a case where an HFT (guard mask not shown) is affixed to a homogeneous test specimen of known
thermal resistance.
7. Procedure
7.1 Use a guarded-hot-plate, thin-heater, heat-flow-meter, or hot box apparatus to calibrate the HFT/stack assembly and follow the
test procedure of either Test Method C177, C518, C1114, or C1363, respectively.
FIG. 4 Surface Mounted HFT Configuration (Side View)
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7.1.1 For apparatuses that typically require two specimens follow Practice C1044 for operation of the apparatus in the single-sided
mode.
7.1.2 For calibration under cryogenic conditions, utilize the appropriate apparatus and test procedure described in Guide C1774.
7.2 Install the HFT/test stack assembly in the apparatus and connect the voltage output leads from the HFT(s) and temperature
sensor(s) to the appropriate readout instrumentation. The presence of air
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