oSIST prEN 12667:2025

SLOVENSKI STANDARD
01-december-2025
Toplotne karakteristike gradbenih materialov in proizvodov - Ugotavljanje toplotne
upornosti z zaščiteno vročo ploščo in merilniki toplotnih tokov - Proizvodi z
visoko in srednjo toplotno upornostjo
Thermal performance of building materials and products - Determination of thermal
resistance by means of guarded hot plate and heat flow meter methods - Products of
high and medium thermal resistance
Wärmetechnisches Verhalten von Baustoffen und Bauprodukten - Bestimmung des
Wärmedurchlasswiderstandes nach dem Verfahren mit dem Plattengerät und dem
Wärmestrommessplatten-Gerät - Produkte mit hohem und mittlerem
Wärmedurchlasswiderstand
Performance thermique des matériaux et produits pour le bâtiment - Détermination de la
résistance thermique par la méthode de la plaque chaude gardée et la méthode
fluxmétrique - Produits de haute et moyenne résistance thermique
Ta slovenski standard je istoveten z: prEN 12667
ICS:
91.100.60 Materiali za toplotno in Thermal and sound insulating
zvočno izolacijo materials
91.120.10 Toplotna izolacija stavb Thermal insulation of
buildings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
prEN 12667
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 91.100.01; 91.120.10 Will supersede EN 12667:2001
English Version
Thermal performance of building materials and products -
Determination of thermal resistance by means of guarded
hot plate and heat flow meter methods - Products of high
and medium thermal resistance
Performance thermique des matériaux et produits Wärmetechnisches Verhalten von Baustoffen und
pour le bâtiment - Détermination de la résistance Bauprodukten - Bestimmung des
thermique par la méthode de la plaque chaude gardée Wärmedurchlasswiderstandes nach dem Verfahren mit
et la méthode fluxmétrique - Produits de haute et dem Plattengerät und dem Wärmestrommessplatten-
moyenne résistance thermique Gerät - Produkte mit hohem und mittlerem
Wärmedurchlasswiderstand
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 89.
If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

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. prEN 12667:2025 E
worldwide for CEN national Members.

prEN 12667 (E)
Contents Page
European foreword . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, symbols and units . 7
3.1 Terms and definitions . 7
3.1.1 certified reference material . 7
3.1.2 internal reference material: (stable with time, with moisture) . 7
3.1.3 hygroscopic material . 7
3.1.4 thermal conductivity, λ, at a point P . 7
3.1.5 thermally homogeneous medium . 7
3.1.6 porosity, ξ . 7
3.1.7 homogeneous porous medium . 8
3.1.8 thermally isotropic medium . 8
3.1.9 thermally stable medium . 8
3.1.10 mean thermal conductivity of a specimen . 8
3.1.11 transfer factor of a specimen . 8
3.1.12 thermal transmissivity of a material . 8
3.1.13 steady state heat transfer property . 9
3.1.14 settling time . 9
3.1.15 room temperature . 9
3.1.16 rigid specimen . 9
3.1.17 ambient temperature . 9
3.1.18 operator . 9
3.1.19 designer . 9
3.1.20 data user . 9
3.2 Symbols and units . 9
4 Principle . 10
4.1 Apparatus . 10
4.2 Measuring the density of heat flow rate . 10
4.3 Measuring the temperature difference . 10
4.4 Deriving the thermal resistance or transfer factor . 11
4.5 Computing thermal conductivity or thermal transmissivity . 11
4.6 Apparatus limits . 11
4.7 Specimen limits . 11
5 Apparatus . 11
5.1 General . 11
5.2 Guarded hot plate apparatus . 12
5.2.1 General . 12
5.2.2 Two specimen apparatus . 13
5.2.3 Single specimen apparatus . 13
5.2.4 Heating unit . 13
5.2.5 Metering area  . 13
5.2.6 Edge insulation and auxiliary guards . 13
5.2.7 Cooling units . 13
5.2.8 Accuracy and repeatability . 13
5.3 Heat flow meter apparatus . 14
5.3.1 General . 14
5.3.2 Heat flow meters . 14
5.3.3 Calibration principle . 14
5.3.4 Limitations due to the calibration . 15
5.3.5 Accuracy and repeatability . 15
6 Test specimens . 16
prEN 12667 (E)
6.1 General . 16
6.2 Selection and size . 16
6.3 Specimen preparation . 16
6.3.1 Conformity with product standards . 16
6.3.2 All specimens except loose-fills . 16
6.3.3 Loose-fill materials . 17
6.3.4 Super insulation material . 17
7 Testing procedure . 17
7.1 General . 17
7.2 Conditioning . 18
7.3 Measurements . 18
7.3.1 Mass . 18
7.3.2 Thickness and density . 18
7.3.3 Temperature difference selection . 18
7.3.4 Ambient conditions . 18
7.3.5 Heat flow rate measurements . 19
7.3.6 Cold surface control (for two-specimen guarded hot plate apparatus) . 19
7.3.7 Temperature difference detection . 19
7.3.8 Settling time and measurement interval . 19
7.3.9 Final mass and thickness measurements . 19
8 Calculations . 20
8.1 Density and mass changes . 20
8.1.1 Densities . 20
8.1.2 Mass changessities . 20
8.2 Heat transfer properties . 20
8.2.1 General . 21
8.2.2 Guarded hot plate apparatus measurements . 21
8.2.3 Heat flow meter apparatus measurements . 21
9 Test report . 22
Annex A (normative) Limitations to the implementation of the measurement principle
and on measurable properties . 24
A.1 Introduction: heat transfer and measured properties . 24
A.2 Limitations due to the implementation of the principle . 24
A.2.1 General . 25
A.2.2 Specimen homogeneity . 25
A.2.3 Maximum specimen thickness . 25
A.2.4 Minimum specimen thickness . 26
A.2.5 Maximum limits for the thermal resistance . 27
A.2.6 Flatness and contact resistances . 27
A.2.7 Parallelism . 27
A.2.8 Limits to temperature difference . 27
A.2.9 Maximum operating temperature . 28
A.2.10 Warping . 28
A.2.11 Settling time and measurement interval . 28
A.3 Limitations on measurable heat transfer properties . 29
A.3.1 General . 29
A.3.2 Thermal resistance, thermal conductance or transfer factor . 30
A.3.3 Mean thermal conductivity or thermal transmissivity of a specimen . 30
A.3.4 Thermal conductivity or thermal transmissivity of a material . 30
A.4 Preliminary decisions . 30
Annex B (normative) Limits for equipment performance and test conditions - Guarded hot
plate . 32
B.1 General . 32
B.2 Accuracy and repeatability, stability, uniformity . 32
B.3 Suggested apparatus sizes . 33
prEN 12667 (E)
B.4 Equipment design requirements . 33
B.5 Acceptable specimen characteristics . 35
B.6 Acceptable testing conditions . 36
Annex C (normative) Limits for equipment performance and test conditions - Heat flow
meter . 38
C.1 General . 38
C.2 Accuracy and repeatability, stability, uniformity . 38
C.3 Equipment design requirements . 40
C.4 Acceptable specimen characteristics . 41
C.5 Acceptable testing conditions . 43
Annex D (normative) Equipment design . 45
D.1 General . 45
D.2 Guarded hot plate apparatus . 45
D.3 Heat flow meter apparatus . 52
Annex E (informative) Guidelines and uncertainty budget to measure thermal resistance
of Vacuum Insulation Panels (VIPs) and determination of linear thermal
transmittance of VIPs . 57
E.1 General information on the measurement of thermal resistance of vacuum
insulation panels (VIPs) . 57
E.2 Uncertainty budget for the determination of thermal conductivty of vacuum
insulation panels (VIPs) . 57
E.2.1 General . 57
E.2.2 Guarded Hot Plate (GHP) . 58
E.2.3 Heat Flow Meter (HFM) . 58
E.3 Determination of linear thermal transmittance of vacuum insulation panels (VIPs) . 59
Annex F (informative) Determination of apparatus emissivity . 62
Bibliography . 65
prEN 12667 (E)
European foreword
This document (prEN 12667:2025) has been prepared by Technical Committee CEN/TC 89 "Thermal
performance of buildings and building components", the secretariat of which is held by SIS.
This document is currently submitted to the CEN Enquiry.
This document is one of a series of standards on thermal test methods which support product standards
for building materials.
This document will supersede EN 12667:2001.
In comparison with the previous edition, the following technical modifications have been made:
— revision of all document to be compliant with CEN rules;
— revision of Clause 3;
— revision of Annex A;
— new Annex E for Vacuum Insulation Panels;
— new Annexe F determination of emissivity;
— new Bibliography.
prEN 12667 (E)
1 Scope
This document spécifiés principles and testing procedures for determining, by means of the guarded
hot plate or heat flow meter methods, the thermal resistance of dry test specimens having a thermal
resistance of not less than 0,5 m ·K/W.
NOTE 1 The above limit is due to the effect of contact thermal resistances. An upper limit for measurable thermal
resistance depends upon a number of factors described in this document, but a unique figuré cannot be assigned.
It applies in principle to any mean test temperature, but the equipment design in Annex D is essentially
intended to operate between a minimum cooling unit temperature of -100 °C and maximum heating
unit temperature of +100 °C.
NOTE 2 Limits to the mean test temperature are only imposed by the materials used in the apparatus
construction and by ancillary equipment.
This document does not supply general guidance and background information (e.g. the heat transfer
property to be reported, product-dependent specimen preparations, procedures requiring multiple
measurements, such as those to assess the effect of specimen non-homogeneities, those to test
specimens whose thickness exceeds the apparatus capabilities, and those to assess the relevance of the
thickness effect).
This document does not apply to cover measurements on moist products of any thermal resistance or
measurements on thick products of high and medium thermal resistance.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8301:1991, Thermal insulation — Determination of steady-state thermal resistance and related
properties — Heat flow meter apparatus
ISO 8302:1991, Thermal insulation — Determination of steady-state thermal resistance and related
properties — Guarded hot plate apparatus
EN 1946-2:1999, Thermal performance of building products and components - Specific criteria for the
assessment of laboratories measuring heat transfer properties - Part 2: Measurements by guarded hot
plate method
EN 1946-2, Thermal performance of building products and components - Specific criteria for the
assessment of laboratories measuring heat transfer properties - Part 2: Measurements by guarded hot
plate method
EN 1946-3, Thermal performance of building products and components - Specific criteria for the
assessment of laboratories measuring heat transfer properties - Part 3: Measurements by heat flow meter
method
EN ISO 7345:2018, Thermal performance of buildings and building components - Physical quantities and
definitions (ISO 7345:2018)
EN 12664, Thermal performance of building materials and products - Determination of thermal resistance
by means of guarded hot plate and heat flow meter methods - Dry and moist products of medium and low
thermal resistance
EN 12939, Thermal performance of building materials and products - Determination of thermal resistance
by means of guarded hot plate and heat flow meter methods - Thick products of high and medium thermal
resistance
prEN 12667 (E)
3 Terms, definitions, symbols and units
For the purposes of this document, the terms and définitions given in EN ISO 7345:2018 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1 Terms and definitions
3.1.1 certified reference material
reference material characterized by a metrologically valid procedure for one or more spécifiéd
properties, accompanied by a reference material cértificaté that provides the value of the spécifiéd
property, its associated uncertainty, and a statement of metrological traceability
Source: EN ISO 17034:2016[1].
3.1.2 internal reference material: (stable with time, with moisture)
Material, sufficiéntly homogeneous and stable with reference to one or more spécifiéd properties (stable
with time, no subject to change properties with moisture), which has been established to be fit for its
intended use in measurement or in examination of nominal properties.
Source: EN ISO 17034:2016[1] , modifiéd, additions of spécific properties and examination of nominal
properties.
3.1.3 hygroscopic material
material which adsorbs, and retains moisture from the environment
NOTE In this standard the hygroscopic material is a material whose mass increases between the dry (dried at
50°C 70°C or 110°C) and the wet state (conditioning at 23 °C 50 %RH) and whose thermal conductivity changes
with moisture.
3.1.4 thermal conductivity, λ, at a point P
Quantity définéd in each point P of a purely conducting medium by the following relation between the
vectors q and grad(T):
q = - λ grad(T)
NOTE In the most general case the thermal conductivity is a nine element tensor and not a constant.
3.1.5 thermally homogeneous medium
medium in which the thermal conductivity is not a function of the position within the medium but may
be a function of the direction, time and temperature
3.1.6 porosity, ξ
total volume of the voids within a porous medium divided by the total volume of the medium
NOTE 1 A porous medium is one which is heterogeneous due to the presence of e.g. fibrés, cell walls, grains.
NOTE 2 The local porosity, ξ , at the point P is the porosity within a specimen when the volume of an elementary
P
part of the specimen is small with respect of the specimen, but large enough to evaluate a meaningful average.
prEN 12667 (E)
3.1.7 homogeneous porous medium
medium in which the local porosity is independent of the point where the value is computed [EN ISO
9251[2]].
NOTE Most high and medium thermal resistance specimens are homogeneous porous, i.e. not homogeneous
(see the définition of porosity) and hence not thermally homogeneous.
3.1.8 thermally isotropic medium
medium in which the thermal conductivity is not a function of the direction but may be a function of the
position within the medium, of time and temperature
NOTE The thermal conductivity of an isotropic medium is définéd through a single value in each point, instead
of a matrix of values.
3.1.9 thermally stable medium
medium in which the thermal conductivity is not a function of time, but may be a function of the co-
ordinates, of temperature and, when applicable, of direction
3.1.10 mean thermal conductivity of a specimen
property définéd in steady state conditions in a body that has the form of a slab bounded by two parallel,
flat isothermal faces and by adiabatic edges perpendicular to the faces, that is made of a material
thermally homogeneous, isotropic (or anisotropic with a symmetry axis perpendicular to the faces),
stable only within the precision of a measurement and the time required to execute it, and with the
thermal conductivity constant or a linear function of temperature
3.1.11 transfer factor of a specimen
factor définéd by
q   d
d
(1)
T = =
∆T R
NOTE This définition is applicable to any steady state test with a guarded hot plate or heat flow meter apparatus
on specimens where conduction, convection and radiation take place together. It depends on experimental
conditions, e.g. temperature difference, apparatus emissivity and specimen thickness, and in these conditions
characterizes a specimen in relation to the combined conduction and radiation heat transfer. It is often referred
to elsewhere as measured, equivalent, apparent or effective thermal conductivity of a specimen.
3.1.12 thermal transmissivity of a material
transmissivity of a material définéd by
∆d
λ =  (2)
t
∆R
when Δd/ΔR is independent of the thickness d.
NOTE The thermal transmissivity is independent of experimental conditions and characterizes an insulating
material in relation with combined conduction and radiation heat transfer. The thermal transmissivity can be
seen as the limit reached by the transfer factor in thick layers where combined conduction and radiation heat
transfer takes place. It is often referred to elsewhere as equivalent, apparent or effective thermal conductivity of
a material.
prEN 12667 (E)
3.1.13 steady state heat transfer property
generic term to identify one of the following properties: thermal resistance, transfer factor, thermal
conductivity, thermal resistivity, thermal transmissivity, thermal conductance, mean thermal
conductivity
3.1.14 settling time
time needed for a measurement to reach steady state conditions within 1 %
3.1.15 room temperature
mean test temperature of a measurement such that a person in a room would regard it comfortable if
it were the temperature of that room
3.1.16 rigid specimen
specimen of a material too hard and unyielding to be appreciably altered in shape by the pressure of
the heating and cooling unit, so as to achieve uniform thermal contact over the entire heating and cooling
unit surfaces facing the specimen.
3.1.17 ambient temperature
Generic term to identify the temperature in the vicinity of the edge of the specimen or in the vicinity of
the whole apparatus
NOTE This temperature is the temperature within the cabinet where the apparatus is enclosed or that of the
laboratory for non-enclosed apparatus
3.1.18 operator
person responsible for carrying out the test and for the presentation through a report of the
measured results
3.1.19 designer
person who develops the constructional details of an equipment in order to meet prédéfinéd
performance limits for the apparatus in assigned testing conditions and who idéntifiés the test
procedures to verify the predicted apparatus accuracy
3.1.20 data user
person involved in the application and interpretation of measured results to judge material or system
performance
3.2 Symbols and units
Table 1 summaries the symbols and units referred to within this document
Table 1 — Symbols and units
Symbol Quantity Unit
A metering area measured on a selected isothermal surface
m
A area of the defect
m
d
A area of the metering section
m
m
R thermal resistance
m ·K/W
T transfer factor W/(m·K)
T temperature of the warm surface of the specimen K
prEN 12667 (E)
Symbol Quantity Unit
T temperature of the cold surface of the specimen K
T mean test temperature (usually (T + T )/2 K
m 1 2
V volume
m
c spécific heat capacity J/(kg·K)
d hickness; average thickness of a specimen m
e edge number ratio -
e heat flow meter output voltage mV
h
f calibration factor of the heat flow meter
W/(mV·m )
m mass (of the specimen)   kg
q density of heat flow rate
W/m
r thermal resistivity   K·m/W
ΔR increments of thermal resistance
m ·K/W
ΔT temperature  difference (usually  T - T ) K
1 2
Δd increments of thickness   m
Δm relative mass change -
Δt time interval s
Φ heat flow rate W
λ thermal conductivity   W/(m·K)
λ thermal transmissivity W/(m·K)
t
ξ porosity -
ξ local porosity -
P
ρ density
kg/m
NOTE The meaning of some additional subscripts is spécifiéd in the text.
4 Principle
4.1 Apparatus
Both the guarded hot plate apparatus and the heat flow meter apparatus are intended to establish within
homogeneous specimens with flat parallel faces, in the form of slabs, a unidirectional constant and
uniform density of heat flow rate. The part of the apparatus where this takes place with acceptable
accuracy is around its centre; the apparatus is therefore divided into a central metering section in which
measurements are taken, and a surrounding guard section.
4.2 Measuring the density of heat flow rate
With the establishment of steady state in the metering section, the density of heat flow rate, q, is
determined from measurement of the heat flow rate, Φ, and the metering area, A, that the heat flow rate
crosses.
4.3 Measuring the temperature difference
The temperature difference across the specimens, ΔT, is measured by temperature sensors fixéd at the
surfaces of the apparatus in contact with the specimen and/or those of the specimens themselves, where
appropriate.
prEN 12667 (E)
4.4 Deriving the thermal resistance or transfer factor
The thermal resistance, R, is calculated from a knowledge of q, A and ΔT if the appropriate conditions
given in A.3.2 are realized. From the additional knowledge of the thickness, d, of the specimen, the
transfer factor, T, is computed.
4.5 Computing thermal conductivity or thermal transmissivity
The mean thermal conductivity, λ or thermal transmissivity λt, of the specimen may also be computed
if the appropriate conditions to identify them and those given in A.4.3 are realised.
4.6 Apparatus limits
The application of the method is limited by the capability of the apparatus to maintain a unidirectional,
constant and uniform density of heat flow rate in the specimen, coupled with the ability to measure
power, temperature and dimensions to the limit of accuracy required, The apparatus shall follow the
information spécifiéd in Annex A.
4.7 Specimen limits
The application of the method is also limited by the shape of the specimen(s) and the degree to which
they are identical in thickness and uniformity of structure (in the case of two specimen apparatus) and
whether their surfaces are flat or parallel Annex A shall be used.
5 Apparatus
5.1 General
A guarded hot plate apparatus or a heat flow meter apparatus used for measurements according to this
document shall comply with the limits on equipment performance and test conditions given in annex
B or annex C of this document and shall conform with the requirements concerning the assessment of
equipment accuracy given in EN 1946-2or EN 1946-3. The equipment design, error analysis and
performance check shall be according to section 2 of ISO 8302:1991 or ISO 8301:1991 respectively.
The equipment shall follow the requirement listed in Annex D. If the equipment used is designed in
accordance with one of these, an error analysis is non mandatory, even though in all cases a performance
check according to EN 1946-2or EN 1946-3 shall be undertaken for the initial assessment of the
equipment.
Unlike the Heat flow meter method, the guarded hot plate apparatus is an absolute apparatus, it shall
not be calibrated. A check with only a single reference sample is not a sufficiént evidence. Temperature
sensors and ancillary instrumentation directly affecting accuracy of results shall be subjected to periodic
calibration with traceability to national measurement standards.
. Its results shall never be corrected using the results of measurements on reference materials. The
equipment design and all the associated instrumentation shall be checked until the cause of
disagreement has been idéntifiéd and réctifiéd. It is recommended that a vérification with one or more
reference materials be performed after the initial performance check required by 2.4 of ISO
8302:1991[4] and at regular intervals e.g. once a year.
Comparative test methods (e.g. the heat flow meter method) require a calibration of the heat flow rate
transducer, in addition to the calibrations applicable to absolute test methods.
The ancillary equipment requiring periodic calibration checks include: digital voltmeters, power
supplies, voltage and current transducers, standard resistances, thickness transducers, etc.
As impacted by ISO 8301:1991/Amd 1:2010[3] .
prEN 12667 (E)
Equipment maintenance actions and the results of calibrations shall be annotated in the calibration,
maintenance filés and update the uncertainty budget if necessary.
5.2 Guarded hot plate apparatus
5.2.1 General
In a guarded hot plate apparatus, the heat flow rate is obtained from the measurement of the power
input to the heating unit in the metering section. The general features of the apparatus with specimens
installed are shown in Figure 1.
There exist two types of guarded hot plate apparatus, which conform to the basic principle outlined in
clause 4:
a) with two specimens (and a central heating unit);
b) with a single specimen.
a) Two-specimen apparatus
Key
A Metering section heater
B Metering section surface plates
C Guard section heater
D Guard section surface plates
E Cooling unit
E Cooling unit surface plate
E Differential thermocouples
g
F Heating unit surface thermocouple
G Cooling unit surface thermocouples
H Test specimen
I Test specimen
L Guard plate
M Guard plate insulation
N Guard plate differential thermocouples
b) Single-specimen apparatus
Figure 1
prEN 12667 (E)
The gap is the separation between metering
section (see A and B) and the guard section (see
C and D)
b) Single-specimen apparatus
Figure 1
5.2.2 Two specimen apparatus
In the two specimen apparatus see a) , a central round or square flat plate assembly, consisting of a
heater and metal surface plates, called the heating unit, is sandwiched between two nearly identical
specimens. The heat flow rate is transferred through the specimens to separate round or square
isothermal flat assemblies, called the cooling units.
5.2.3 Single specimen apparatus
In the single specimen apparatus seeb), one of the specimens is replaced by a combination of a piece of
insulation and a guard plate. A zero temperature-difference is then established across this combination.
Providing all other applicable requirements of this document are fulfilléd, accurate measurements and
reporting according to this method may be accomplished with this type of apparatus.
5.2.4 Heating unit
The heating unit consists of a separate central metering section, where the unidirectional constant and
uniform density of heat flow rate can be established, surrounded by a guard section separated by a
narrow gap.
5.2.5 Metering area
The metering area is the central area of the specimen delimited by the centre line of the gap of the
heating unit.
This définition, which applies in principle to thick specimens only, has been retained for all the
specimens to be tested according to this standard: due to this approximation, the thickness of the
specimen shall be at least ten times the width of the gap.
5.2.6 Edge insulation and auxiliary guards
Additional edge insulation and/or auxiliary guard sections shall be used when operating above orbelow
room temperature, in accordance with Annex B of EN 1946-2:1999.
5.2.7 Cooling units
The cooling units shall have dimensions at least as large as those of the heating unit, including the guard
heater(s). They shall consist of metal plates maintained at a constant and uniform temperature.
5.2.8 Accuracy and repeatability
Accuracy and repeatability depend both on the equipment and on testing conditions. The complete
assessment of testing errors in a guarded hot plate apparatus in any spécific testing condition shall be
carried out in accordance with EN 1946-2. The following is rough information applicable for tests
correctly executed when the mean temperature of the test is near the room temperature.
Equipment constructed and operated in accordance with this document shall be in accordance with
Annex B and capable of measuring an accuracy within ± 2 %.
The repeatability of subsequent measurements made by the equipment on a specimen maintained
within the apparatus without changes in testing conditions shall be ± 0,5 %.
prEN 12667 (E)
When measurements are made on the same reference specimen removed and then mounted again, the
repeatability of measurements shall be
...