Heat Loss Estimator
Estimate steady heat transfer through a surface from its overall U-value, surface area and temperature difference, with optional duration-to-energy conversion.
How to use this calculator
- Enter U-value, surface area, temperature difference and duration.
- Confirm that all inputs use the stated units and the same population, period or scope.
- Change one assumption at a time when comparing scenarios.
Formula used by the heat loss estimator calculator
Q̇ = U × A × ΔT
- Q̇ = U × A × ΔT
- Steady-state estimate only; air leakage, thermal bridges, solar gains and changing conditions are excluded.
- Inputs are validated against required ranges and outputs are rounded for readability.
Worked examples
Worked example
U=0.8 W/m²K, area 20 m² and temperature difference 20 K.
Estimated heat transfer rate is 320 W.
Estimated heat transfer rate is 320 W.
Understanding the result
Estimate steady heat transfer through a surface from its overall U-value, surface area and temperature difference, with optional duration-to-energy conversion.
Steady-state estimate only; air leakage, thermal bridges, solar gains and changing conditions are excluded.
Important notes
Steady-state estimate only; air leakage, thermal bridges, solar gains and changing conditions are excluded.
Use the result as a calculation aid for the inputs supplied; confirm critical specifications independently.
Frequently asked questions
What does a U-value represent?
It expresses heat transfer per square metre per degree of temperature difference.
Does this size a heating system?
No; whole-building loads need more complete heat-loss and ventilation calculations.
How do I use this calculator?
Enter U-value, surface area, temperature difference and duration.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.