ISO 10291:1994

Overview

ISO 10291:1994 specifies a standardized method for determining the steady-state thermal transmittance (U-value) of multiple glazing used in building applications. This international standard applies to multiple glazing units with flat and parallel surfaces, including cast and figured rolled glass, commonly found in windows and facades. The method excludes edge effects and solar radiation influences, focusing on the core thermal performance of glazing systems.

The determination of U-values is performed using the guarded hot plate technique, which allows precise measurement of heat transfer through glazing materials. By establishing uniform testing conditions representative of typical building environments, ISO 10291:1994 ensures reliable and comparable thermal performance data for multiple glazing products.

Key Topics

• Scope of Application Applies to multiple glazing with outer panes non-transparent to far-infrared radiation (typical window glass), and internal elements which may be transparent to far-infrared.

• Guarded Hot Plate Method Involves placing two similar specimens on either side of a heating unit; heat flow is measured to calculate thermal resistance and U-values.

• Specimen Requirements

  • Square specimens, preferably 800 mm x 800 mm, with size tolerance from 750 mm to 850 mm.
  • Surface flatness and parallelism are critical; bowing or dishing must not exceed 0.5 mm.
  • Thickness consistency between two specimens limited to 2%.

• Measurement Conditions

  • Mean specimen temperature: (10 ± 0.5) °C
  • Temperature difference between hot and cold sides: (15 ± 1) °C
  • Use of natural rubber sponges ensures optimal thermal contact.

• Calculation of U-Value U-value (W/m²K) is calculated from the measured thermal resistance (R) and standardized surface heat transfer coefficients (hi and he). Adjustments apply when low-emissivity (low-E) coatings are present.

• Test Report Requirements Detailed reporting includes specimen dimensions, materials, layer details, temperature values, surface heat transfer coefficients, measured U-value and thermal resistance.

Applications

ISO 10291:1994 is essential for:

• Building Design and Energy Efficiency Enables architects and engineers to select glazing that meets energy codes by quantifying thermal insulation performance.

• Product Certification and Quality Control Manufacturers use this standard method for product testing to provide accurate thermal transmittance data.

• Research and Development Facilitates development of advanced glazing technologies-such as multi-pane, coated, or gas-filled units-by allowing precise thermal performance comparisons.

• Regulatory Compliance Supports compliance with international and local building regulations requiring verified U-values for glazing products.

• Consulting and Retrofitting Helps energy consultants assess and recommend glazing upgrades to improve building thermal performance.

Related Standards

• ISO 8302:1991 – Thermal insulation – Determination of steady-state thermal resistance and related properties using the guarded hot plate apparatus. Provides detailed apparatus requirements referenced in ISO 10291.

• ISO 10292:1994 – Glass in building – Calculation of steady-state U-values of multiple glazing. Complements ISO 10291 by specifying calculation methods based on measured data.

• EN 673 – Glass in building – Determination of thermal transmittance (U value) – Heat flow meter method.

• ASTM C1363 – Standard test method for thermal performance of building materials and envelope assemblies.

Keywords: ISO 10291, multiple glazing, thermal transmittance, U-value, guarded hot plate method, glass in building, thermal insulation, steady-state measurement, window glass, energy efficiency, building standards.