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Hotbox Test Chambers

Hotbox test chambers are used to determine the stationary heat transfer properties of complex components and finished products used for construction, such as doors, windows, profiles, domes and brickwork.


The heat transfer coefficient (u-value) measures the heat transfer that takes place at a component when there is a temperature difference in the ambient atmosphere. The measurement unit is W/m² · K (Watts per square meter x Kelvin). The u-value indicates the heat flow (thermal energy per time unit) per area of the building component and per Kelvin temperature difference. The heat transfer coefficient is dependent on the heat transfer coefficients between the building component and the ambient air as well as the thermal conductivity and geometry of the building component. The u-value is also influenced by surface effects such as heat radiation and convection. The heat transfer coefficient is measured in the steady state to eliminate the influence of the heat storage capacity of the building components.The lower the heat transfer coefficient the better the insulating properties of the material.

The total thermal resistance / overall heat transfer resistance R in (K·m²)/W is calculated from the reciprocal of the heat transfer coefficient (1/U).

Measuring Methods: with Heat Flow Meter and with Guarded Hotbox

Depending on the component to be tested, one of the following methods is used:

  • with heat flow meter according to DIN EN 1934
  • with guarded hotbox according to DIN EN ISO 8990