Overview
ISO 8302:1991 - Thermal insulation - Determination of steady-state thermal resistance and related properties - Guarded hot plate apparatus - specifies the guarded hot plate method for measuring steady-state heat transfer through flat slab specimens and calculating their heat transfer properties. It is an absolute (primary) method that requires only measurements of length, temperature and electrical power. Annex A is integral; Annexes B, C and D provide informative guidance.
Keywords: ISO 8302:1991, guarded hot plate, thermal insulation, steady-state thermal resistance, thermal conductivity, transfer factor.
Key topics and requirements
- Method scope: measurement of steady-state heat flow through flat slab specimens and derivation of properties such as thermal resistance, thermal conductance, mean thermal conductivity, and transfer factor (apparent/effective conductivity).
- Document structure: three main sections covering General principles, Apparatus and error evaluation, and Test procedures, plus annexes on performance limits, thermocouples, maximum specimen thickness and bibliography.
- Apparatus: design requirements, performance checks and error evaluation for a guarded hot plate apparatus. Designers are given latitude in geometry but must meet specified performance limits (see Annex A).
- Measurement essentials: only length, temperature and electrical power measurements are required; recommended good laboratory practice and operator expertise in heat transfer and low-level electrical/temperature measurement.
- Specimen requirements and limitations:
- Dried specimens recommended; moisture effects are complex and not covered in detail.
- Radiation and possible internal convection can affect results - orientation, thickness and temperature difference must be reported.
- Results may be reported as thermal conductance/resistance or transfer factor when specimen conditions are limited; full mean thermal conductivity can be reported only when stricter specimen requirements are met.
- Accuracy notes: reports should not claim measurements for specimens with thermal resistance below 0.1 m2·K/W (though values as low as 0.02 m2·K/W are possible with reduced accuracy).
Practical applications
- Laboratory measurement and certification of insulation materials (mineral wool, foams, board materials).
- Development and verification of thermal models and product datasheets.
- Inter-laboratory comparisons and reference testing to validate guarded hot plate apparatus performance.
- Research into radiative, conductive and convective contributions to heat transfer in porous insulating materials.
Who should use this standard
- Test laboratories and quality-control facilities measuring thermal properties.
- Instrument designers and manufacturers of guarded hot plate apparatus.
- Material scientists, building physics engineers, and product developers specifying insulation performance.
- Data users applying measured thermal properties in simulations, product selection or regulatory compliance.
Related standards
Normative and related references in the standard include: ISO 7345, ISO 9229, ISO 9251, ISO 9288, ISO 9346 - for definitions, terminology and related heat-transfer concepts.