SIST EN ISO 8894-2:2026

Refractory materials - Determination of thermal conductivity - Part 2: Hot-wire method (parallel) (ISO 8894-2:2007)

This part of ISO 8894 describes a hot-wire (parallel) method for the determination of the thermal conductivity of refractory products and materials. It is applicable to dense and insulating shaped products and to powdered or granular materials (see 6.2), for thermal conductivities of less than 25 W/m·K. The limits are imposed by the thermal diffusivity of the test material and therefore by the dimensions of the test pieces; higher thermal conductivities can be measured if larger pieces are used. Electrically conducting materials cannot be measured.
NOTE 1 The thermal conductivity of products with a hydraulic or chemical bond can be affected by the appreciable amount of water that is retained after hardening or setting and is released on firing. These materials can therefore require pretreatment. The nature and extent of such pretreatment, and the period for which the test piece is held at the measurement temperature as a preliminary to carrying out the test, are details that are outside the scope of this part of ISO 8894 and are agreed between the parties concerned.
NOTE 2 In general, it is difficult to make measurements on anisotropic materials and the use of this method for such materials is also agreed between the parties concerned.

Feuerfeste Werkstoffe - Bestimmung der Wärmeleitfähigkeit - Teil 2: Heißdraht-Verfahren (Paralleldraht-Verfahren) (ISO 8894-2:2007)

Matériaux réfractaires - Détermination de la conductivité thermique - Partie 2: Méthode du fil chaud (parallèle) (ISO 8894-2:2007)

La présente partie de l’ISO 8894 spécifie une méthode de détermination de la conductivité thermique des matériaux et produits réfractaires par la méthode du fil chaud (parallèle). Elle s’applique aux produits façonnés denses et isolants, et aux matériaux en poudre et en grains (voir 6.2), pour des conductivités thermiques inférieures à 25 W/m·K. Ces limites sont imposées par la diffusivité thermique du matériau soumis à l’essai et donc par les dimensions des éprouvettes. Des conductivités thermiques plus élevées peuvent être mesurées si l’on utilise de plus grandes éprouvettes. Les matériaux électriquement conducteurs ne peuvent pas être soumis à cette mesure.
NOTE 1   La conductivité thermique des produits liés (liaison chimique ou hydraulique) peut être modifiée par la quantité d’eau notable retenue après le durcissement ou la prise puis libérée à la cuisson. Ces matériaux peuvent donc nécessiter un prétraitement; la nature et l’importance de ce prétraitement, ainsi que la durée de maintien de l’éprouvette à la température de mesure, étant préliminaires à l’exécution de l’essai proprement dit, sont des détails qui ne relèvent pas de l’objet de la présente partie de l’ISO 8894, et ils devraient faire l’objet d’un accord entre les parties concernées.
NOTE 2   Il est en général difficile de procéder à des mesures sur des matériaux anisotropes et l’application de la présente méthode à ces matériaux devrait également faire l’objet d’un accord entre les parties concernées.

Ognjevzdržni materiali - Ugotavljanje toplotne prevodnosti - 2. del: Metoda vroče (vzporedna) žice (ISO 8894-2:2007)

General Information

• Status: Published
• Public Enquiry End Date: 30-Oct-2025
• Publication Date: 28-Dec-2025
• ICS: 81.080 - Refractories
• Technical Committee: IKER - Ceramics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 19-Dec-2025
• Due Date: 23-Feb-2026
• Completion Date: 29-Dec-2025
• Ref Project: EN ISO 8894-2:2025 - Refractory materials - Determination of thermal conductivity - Part 2: Hot-wire method (parallel) (ISO 8894-2:2007)

Relations

• Revises: SIST EN 993-15:2005 - Methods of test for dense shaped refractory products - Determination of thermal conductivity by the hot-wire (parallel) method
• Effective Date: 04-Jun-2025

Overview

EN ISO 8894-2:2025 (ISO 8894-2:2007) defines the hot‑wire (parallel) method for determining the thermal conductivity of refractory materials and products. The method is applicable to dense and insulating shaped products as well as powdered or granular materials for thermal conductivities typically below 25 W·m−1·K−1 (higher values are measurable with larger test pieces). The technique measures the temperature rise versus time from a linear heat source (hot wire) embedded between two test pieces and uses a differential thermocouple to derive thermal conductivity.

Keywords: refractory materials, thermal conductivity, hot‑wire method, EN ISO 8894‑2:2025, ISO 8894‑2, thermocouple, thermal diffusivity.

Key topics and technical requirements

• Principle: temperature increase measured at a fixed distance from an embedded linear heater (hot wire) after current is applied; thermal conductivity calculated from temperature‑time response.
• Test assembly: two identical test pieces (minimum 200 × 100 × 50 mm; recommended 230 × 114 × 64 mm or 230 × 114 × 76 mm). Surface flatness between contacting faces ≤ 0.2 mm over ≥100 mm.
• Hot wire and measurement length: voltage taps typically separated by about 200 mm (±0.5 mm). Hot wire material preferably platinum or platinum‑rhodium.
• Thermocouple: differential Type R or S (platinum/platinum‑rhodium) with measurement leads running parallel to the hot wire at 15 mm ± 1 mm.
• Furnace and temperature control: electrically heated furnace up to 1 250 °C; temperature uniformity in test region within ±10 K, and external test‑assembly temperature stable to ±0.5 K during measurement.
• Power and instrumentation: stabilized power supply (AC or DC) with power stability within ±2 %; minimum power density 250 W/m (≈50 W for 200 mm measurement length). Digital multimeter accuracy ≥ ±0.5 %. Data acquisition sensitivity ~0.01 K and time resolution < 0.5 s.
• Special cases: powdered/granular tests use non‑reactive containers sized to match solid assembly; electrically conducting refractory materials cannot be measured by this method.

Applications and users

• Quality control and acceptance testing of refractory bricks, castables and insulating materials.
• R&D and product development for refractory manufacturers and material scientists assessing thermal performance.
• Independent test laboratories and certification bodies performing standardized thermal conductivity measurements.
• Furnace, kiln and high‑temperature equipment designers who need validated thermal properties for thermal modelling and insulation selection.

Related standards

• EN ISO 8894‑1 / ISO 8894‑1 - Hot‑wire method (cross‑array) for complementary measurement arrangements.
• EN 993‑15 - Related European standard; EN ISO 8894‑2 is technically aligned with EN 993‑15.

This standard provides a reproducible, instrumented procedure for measuring thermal conductivity of refractory materials under controlled high‑temperature conditions, supporting material selection, product specification and thermal design.

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2026
Ognjevzdržni materiali - Ugotavljanje toplotne prevodnosti - 2. del: Metoda vroče
(vzporedna) žice (ISO 8894-2:2007)
Refractory materials - Determination of thermal conductivity - Part 2: Hot-wire method
(parallel) (ISO 8894-2:2007)
Feuerfeste Werkstoffe - Bestimmung der Wärmeleitfähigkeit - Teil 2: Heißdraht-
Verfahren (Paralleldraht-Verfahren) (ISO 8894-2:2007)
Matériaux réfractaires - Détermination de la conductivité thermique - Partie 2: Méthode
du fil chaud (parallèle) (ISO 8894-2:2007)
Ta slovenski standard je istoveten z: EN ISO 8894-2:2025
ICS:
81.080 Ognjevzdržni materiali Refractories
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 8894-2
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2025
EUROPÄISCHE NORM
ICS 81.080 Supersedes EN 993-15:2005
English Version
Refractory materials - Determination of thermal
conductivity - Part 2: Hot-wire method (parallel) (ISO
8894-2:2007)
Matériaux réfractaires - Détermination de la Feuerfeste Werkstoffe - Bestimmung der
conductivité thermique - Partie 2: Méthode du fil chaud Wärmeleitfähigkeit - Teil 2: Heißdraht-Verfahren
(parallèle) (ISO 8894-2:2007) (Paralleldraht-Verfahren) (ISO 8894-2:2007)
This European Standard was approved by CEN on 7 December 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8894-2:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 8894-2:2007 has been prepared by Technical Committee ISO/TC 33 "Refractories” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 8894-2:2025 by
Technical Committee CEN/TC 187 “Refractory products and materials” the secretariat of which is held
by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2026, and conflicting national standards shall be
withdrawn at the latest by June 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 993-15:2005.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 8894-2:2007 has been approved by CEN as EN ISO 8894-2:2025 without any
modification.
INTERNATIONAL ISO
STANDARD 8894-2
Second edition
2007-12-15
Refractory materials — Determination of
thermal conductivity —
Part 2:
Hot-wire method (parallel)
Matériaux réfractaires — Détermination de la conductivité thermique —
Partie 2: Méthode du fil chaud (parallèle)

Reference number
ISO 8894-2:2007(E)
©
ISO 2007
ISO 8894-2:2007(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2007 – All rights reserved

ISO 8894-2:2007(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Terms and definitions. 1
3 Principle. 2
4 Apparatus . 2
5 Test pieces . 4
6 Procedure . 5
7 Assessment of results. 7
8 Calculation and expression of results. 7
9 Precision. 9
10 Test report . 9
Annex A (informative) Example of the determination of thermal conductivity. 10
Bibliography . 13

ISO 8894-2:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 8894-2 was prepared by Technical Committee ISO/TC 33, Refractories.
This second edition cancels and replaces the first edition (ISO 8894-2:1990), which has been technically
revised to be technically identical to EN 993-15. The main changes are the following. (Note that the clause
and subclause references given below refer to the 1990 edition.)
The Scope has been revised. It contains all the essential elements of ISO 8894-2:1990 except that the
1 250°C temperature limit has been omitted. In Note 2, reference to fibres has been taken out as current
practice allows measurements on these materials.
Clause 2 Normative references has been deleted because
⎯ sampling for this test is not usually carried out in accordance with ISO 5022, and
⎯ ISO 8894-1 is only referred to in the Scope and not in the method itself.
The definitions given in Clause 3 have been improved and clarified.
The accuracy of temperature measurement of the furnace, given in 5.1, has been reduced to ± 10 K.
Modifications to 5.2 to 5.4 reflect equipment currently in use.
A paragraph has been added to 5.7 to ensure that the container is inert under the test conditions.
Subclause 6.4 and Figure 4 have been modified to allow grooves in one test piece only, for simplicity of
machining. Bedding material has been removed from Figure 4 as it has been found to affect the results due to
heat-transfer modification. A tolerance has been given for surface flatness of the test pieces, so that bedding
material is not required.
Subclause 7.2 has been modified to ensure stability of the hot wire and measurement thermocouple.
Table 1 has been modified to reflect modern equipment and 7.5 has been changed accordingly.
A new Clause 7 has been added between 7.11 and Clause 8 to ensure test accuracy.
iv © ISO 2007 – All rights reserved

ISO 8894-2:2007(E)
In the equation In Clause 8, V.I has been replaced by P, the rate of energy transfer, as stated in the definitions
in Clause 3.
Annex A has been updated for current practice.
ISO 8894 consists of the following parts, under the general title Refractory materials — Determination of
thermal conductivity:
⎯ Part 1: Hot-wire method (cross-array)
⎯ Part 2: Hot-wire method (parallel)

INTERNATIONAL STANDARD ISO 8894-2:2007(E)

Refractory materials — Determination of thermal
conductivity —
Part 2:
Hot-wire method (parallel)
1 Scope
This part of ISO 8894 describes a hot-wire (parallel) method for the determination of the thermal conductivity
of refractory products and materials. It is applicable to dense and insulating shaped products and to powdered
or granular materials (see 6.2), for thermal conductivities of less than 25 W/m·K. The limits are imposed by the
thermal diffusivity of the test material and therefore by the dimensions of the test pieces; higher thermal
conductivities can be measured if larger pieces are used. Electrically conducting materials cannot be
measured.
NOTE 1 The thermal conductivity of products with a hydraulic or chemical bond can be affected by the appreciable
amount of water that is retained after hardening or setting and is released on firing. These materials can therefore require
pretreatment. The nature and extent of such pretreatment, and the period for which the test piece is held at the
measurement temperature as a preliminary to carrying out the test, are details that are outside the scope of this part of
ISO 8894 and are agreed between the parties concerned.
NOTE 2 In general, it is difficult to make measurements on anisotropic materials and the use of this method for such
materials is also agreed between the parties concerned.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
thermal conductivity
λ
density of heat flow rate divided by the temperature gradient
NOTE Thermal conductivity is expressed in watts per metre kelvin (W/m·K).
2.2
thermal diffusivity
a
thermal conductivity divided by the bulk density times the specific heat capacity
λ
NOTE 1 a=
ρ⋅ c
p
where
λ is the thermal conductivity;
ρ is the bulk density;
c is the specific heat capacity at constant pressure per weight.
p
2 −1
NOTE 2 Thermal diffusivity is expressed in square metres per second (m s ).
ISO 8894-2:2007(E)
2.3
power
P
rate of energy transfer
NOTE Power is expressed in watts (W).
3 Principle
The hot-wire method (parallel) is a dynamic measuring procedure based on the determination of the
temperature increase against time at a certain location and at a specified distance from a linear heat source
embedded between two test pieces.
The test pieces are heated in a furnace to a specified temperature and maintained at that temperature.
Further local heating is provided by a linear electrical conductor (the hot wire) that is embedded in the test
piece and carries an electrical current of known power that is constant in time and along the length of the test
piece.
A thermocouple is fitted at a specified distance from the hot wire, the thermocouple leads running parallel to
the wire (see Figure 1). The increase in temperature as a function of time, measured from the moment the
heating current is switched on, is a measure of the thermal conductivity of the material from which the test
pieces are made.
4 Apparatus
4.1 Furnace, electrically heated, capable of taking one or more test assemblies (see 5.1) up to a maximum
temperature of 1 250 °C. The temperature at any two points in the region occupied by the test pieces shall not
differ by more than 10 K. The temperature measured on the outside of the test assembly during a test (of
duration about 15 min) shall not vary by more than ± 0,5 K, and shall be known with an accuracy of ± 10 K.
4.2 Hot wire, preferably of platinum or platinum-rhodium, with a minimum length equivalent to that of the
test piece. The voltage taps should be located in the test piece with a length between the taps of about
200 mm known to the nearest ± 0,5 mm.
Both ends of the hot wire are attached to the power source and the voltage taps to the digital multimeter (4.5).
The wires to the power source may also be a continuation of the hot wire itself and shall have the same
diameter as the wire within the assembly. The wires to the digital multimeter shall be of a diameter not greater
than that of the hot wire when within the assembly. Leads outside the assembly shall consist of two or more
tightly twisted wires of 0,5 mm diameter. The current lead connections external to the furnace shall be made
with heavy-gauge cable.
4.3 Power supply, to the hot wire (4.2), which shall be stabilized a.c. or d.c., but preferably a.c., and shall
not vary in power by more than 2 % during the period of measurement.
A power supply to the hot wire of at least 250 W/m is required. This is equivalent to 50 W between the voltage
taps for a distance of 200 mm.
4.4 Differential platinum/platinum-rhodium thermocouple, (Type R: platinum 13 % rhodium/platinum
thermocouple, or Type S: platinum 10 % rhodium/platinum thermocouple, see Table 1) formed from a
measurement thermocouple and a reference thermocouple connected in opposition (see Figure 1). The leads
of the measurement thermocouple shall run parallel to the hot wire at a distance of 15 mm ± 1 mm (see
Figure 2). The output of the reference thermocouple shall be kept stable by placing it between the top outer
face of the upper test piece and a cover of the same material as the test piece (see Figure 1). The diameter of
the measurement thermocouple wires shall be the same as that of the hot wire and the wires of both
thermocouples shall be long enough to extend outside the furnace where connections to the measuring
apparatus shall be made by wire of a different type. The external connections of the thermocouple shall be
isothermal.
An insulating layer may be inserted between the cover and the upper test piece.
NOTE Base-metal thermocouples can be used at temperatures below 1 000 °C.
2 © ISO 2007 – All rights reserved

ISO 8894-2:2007(E)
Key
1 Cover
2 Reference thermocouple
3 Optional insulating layer
4 Test piece
5 Measurement circuit
6 Measurement thermocouple
7 Test piece
8 Heating circuit
9 Voltage taps
Figure 1 — Location of heating circuit and measurement circuit (differential thermocouple circuit)
Dimensions in millimetres
Key
1 Temperature/time registration device
2 Cover
3 Reference thermocouple
4 Measurement thermocouple
5 Hot wire
6 Voltmeter
7 Ammeter
8 Power source
PQ = Hot-wire measurement length

Figure 2 — Measurement arrangement
ISO 8894-2:2007(E)
4.5 Digital multimeter, used for measuring the current in the hot wire and the voltage drop across it, and
capable of measuring both to an accuracy of at least ± 0,5 %.
4.6 Data acquisition system, consisting of a temperature-time registration device with a sensitivity of at
least
...