🧊 Thermal Resistance and Thermal Conductivity λ — Guarded Hot Plate and Heat Flow Meter

Construction PN-EN 12667

Overview

STATUS (as of 06.11.2026). PN-EN 12667:2002 “Właściwości cieplne materiałów i wyrobów budowlanych — Określanie oporu cieplnego metodami osłoniętej płyty grzejnej i czujnika strumienia cieplnego — Wyroby o dużym i średnim oporze cieplnym” (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) — Polish version, published 31.12.2002, implements EN 12667:2001 [IDT]. The card has no withdrawal note — the standard is current. EN 12667:2001 is under revision — the iTeh catalogue shows the draft FprEN 12667 and its Slovenian enquiry adoption oSIST prEN 12667:2025.

SCOPE (clause 1, introduction). The standard specifies the principles and procedure for determining the thermal resistance of specimens with a thermal resistance of not less than 0.5 m²·K/W by the guarded hot plate or heat flow meter method. The lower limit is due to the effect of contact resistances; no single figure can be given for the upper limit. The standard applies in principle to any mean test temperature, and the example apparatus designs of Annex D operate between −100 °C (cooling unit) and +100 °C (heating unit). It does not cover moist products or thick products of high and medium resistance — these are covered by EN 12664 (products of medium and low resistance and moist products) and EN 12939 (thick products). It does not give, among other things, product-dependent specimen preparation or which property is to be reported, so it is used together with the product standard. Intended primarily for building materials, it can be used for specimens of any material that meets its requirements. For routine testing this standard and the product standard are sufficient; complete requirements for both methods are given in ISO 8302:1991 and EN 1946-2:1999 (guarded hot plate) and ISO 8301:1991 and EN 1946-3:1999 (heat flow meter).

PRINCIPLE (clause 4). Both apparatus establish within a homogeneous flat specimen with parallel faces a unidirectional, constant and uniform density of heat flow rate; the measurement takes place in a central metering section surrounded by a guard section. In steady state, the density of heat flow rate q is determined from the heat flow rate Φ and the metering area A, and the temperature difference ΔT by sensors at the surfaces in contact with the specimen (or on the specimen). The thermal resistance R is calculated from q, A and ΔT if the conditions of A.3.2 are met; knowing the thickness d — the transfer factor; the mean thermal conductivity λ or thermal transmissivity λt — if the conditions of A.4.3 are met. The application of the method is limited by the capability of the apparatus (constant heat flow, accuracy of power, temperature and dimension measurements) and by the specimen (shape, identical thickness and uniformity, flatness and parallelism of the faces).

GUARDED HOT PLATE APPARATUS (5.2). The heat flow rate is determined from the power input to the heater of the metering section. Two-specimen apparatus: heating unit between two nearly identical specimens, cooling units behind them; single-specimen apparatus: the second specimen is replaced by insulation with a guard plate across which a zero temperature difference is maintained (this variant is noted in the test report). The metering area extends to the centre line of the gap between metering and guard sections; the specimen thickness shall be at least ten times the gap width. The cooling units are at least as large as the heating unit including the guard. Apparatus built and operated according to the standard measures the properties of products of high and medium resistance to within ± 2 % (at a mean temperature near room temperature); repeatability of successive measurements without changing conditions — typically better than ± 0.5 %, after remounting the specimen — normally better than ± 1 %.

HEAT FLOW METER APPARATUS (5.3). The density of heat flow rate is measured by one or two heat flow meters placed against the specimen: q = f · eh (eh — heat flow meter output, f — calibration factor depending on temperature and, to a lesser extent, on the density of heat flow rate). Configurations: single-specimen asymmetrical, single-specimen symmetrical, two-specimen symmetrical. It is a relative method: the ratio of the resistance of the unknown specimen to that of a standard specimen Ru/Rs = Φs/Φu; calibration according to ISO 8301:1991. The calibration curve must not be extrapolated outside the temperature range, and the apparatus must not be used outside the range of heat flow densities covered by the calibration. The calibration accuracy depends on the reference material and is normally within ± 2 %; when the limits of Annex C are met, the method determines the properties to within ± 3 % (mean temperature near room temperature).

SPECIMENS (6.2). One or two specimens are selected from each sample, depending on the apparatus; two specimens shall be as identical as possible, with thicknesses differing by less than 2 %. The specimens shall cover the surfaces of the heating unit.

WHAT WE DO NOT GIVE HERE. The measurement procedure (clause 7), calculations and test report and Annexes A–D — they are outside the available preview. Specimen dimensions, plate temperatures, time to reach steady state and conditioning — they depend on the apparatus and the product standard. λ values for materials and the determination of declared values — they are not part of this standard.

Method principle

A flat specimen with parallel faces is placed between a heating unit and a cooling unit and brought to steady-state unidirectional heat flow in the metering section, surrounded by a guard section. In the guarded hot plate method the heat flow rate is determined from the power of the metering section heater, in the heat flow meter method — from the output of a heat flow meter calibrated on a standard specimen (Ru/Rs = Φs/Φu).

From the density of heat flow rate q = Φ / A and the temperature difference ΔT across the specimen faces, the thermal resistance R = ΔT / q is calculated, and when the conditions of the standard are met — the thermal conductivity λ = d / R (d — specimen thickness).

Applications

• Thermal resistance of building products of high and medium thermal resistance (at least 0.5 m²·K/W) — together with the product standard
• Thermal conductivity λ or thermal transmissivity λt of the specimen — when the conditions of A.4.3 of the standard are met
• Testing of specimens of other materials meeting the requirements of the standard (clause 1)
• Not applicable: moist products and products of low resistance (EN 12664) or thick products (EN 12939)

Key parameters

Standard

Standard number

PN-EN 12667:2002

Title (PL)

Właściwości cieplne materiałów i wyrobów budowlanych — Określanie oporu cieplnego metodami osłoniętej płyty grzejnej i czujnika strumienia cieplnego — Wyroby o dużym i średnim oporze cieplnym

Title (EN)

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

Step-by-step procedure

1. Apparatus

   The apparatus shall meet the limits of Annex B (guarded hot plate) or C (heat flow meter) and the requirements of EN 1946-2:1999 or EN 1946-3:1999; apparatus built according to Annex D needs no error analysis but needs a performance check (5.1, 5.4).

2. Calibration (heat flow meter)

   Calibrate the apparatus on a standard specimen according to ISO 8301:1991; do not extrapolate outside the temperature range and heat flow density range covered by the calibration (5.3.3–5.3.4).

3. Specimens

   Select one or two specimens according to the type of apparatus; two specimens as identical as possible, thicknesses differing by less than 2 %; the specimens cover the surfaces of the heating unit. Decisions on preparation and test conditions — according to the standard and the product standard (clause 6).

4. Steady-state measurement

   Once steady state is established in the metering section, determine the heat flow rate (heater power or heat flow meter output) and the temperature difference across the specimen faces (clause 4).

5. Calculations

   Calculate the density of heat flow rate q = Φ / A, the thermal resistance R (conditions of A.3.2) and — when the conditions of A.4.3 are met — the thermal conductivity λ (clause 4).

Required equipment and apparatus

Health and safety (OHS)

• The available text of the standard gives no safety requirements — the rules for working at the apparatus with heating and cooling units and for cutting specimens are set by the laboratory on the basis of a risk assessment

Frequently asked questions