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Heat loss calculator — U × A × ΔT

Calculate steady-state fabric heat transfer through one building element from U-value, area and temperature difference.

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How the calculation works

Steady-state transmission heat transfer for the entered element.

Formula

Q = U × A × ΔT

Worked example

U-value0.25 W/m²K
Area100 m²
Temperatures20°C / 0°C
Expected heat transfer500 W

Assumptions and limitations

Assumptions

  • The U-value represents the complete element.
  • Conditions are steady-state.

What this does not check

  • Does not include thermal bridges, infiltration, ventilation, gains or warm-up allowance.
  • Does not produce a complete room or building heat load.
Formula version: 1.0 · Last reviewed: 16 August 2026

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Engineering basis: first-principles calculation using user-entered project data. The calculator does not choose design criteria or replace the complete project-specific engineering design.
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