Steady Heat Loss Calculator
Heat loss rate = U-value × area × temperature difference
Estimate steady heat transfer through an assembly from U-value, area, and temperature difference.
Formula
Heat loss rate = U-value × area × temperature difference
Worked example
U-value: 0.3 W/(m²·K)
Surface area: 50 m²
Temperature difference: 20 K
With these inputs, the result is 300 W.
How to use this calculator
- Identify the quantity you want to calculate.
- Enter your measurements in the units shown on each field.
- Read the result, which updates as you change the inputs.
- Check the assumptions below before applying the result.
Assumptions and limits
Excludes ventilation, thermal bridges, solar gains, and dynamic storage. Not a complete heating-load design.
Precision and checking
Results are rounded for display. Use the most accurate measurements available, and avoid rounding your inputs unnecessarily. Extra decimal places in a result do not make an estimate more reliable.
To check a result, substitute the same input values into the formula shown above. Change one value at a time to understand how the quantity responds.
Frequently asked questions
What assumptions does this calculation use?
Excludes ventilation, thermal bridges, solar gains, and dynamic storage. Not a complete heating-load design.
Are my inputs sent to a server?
No. The calculation runs locally in your browser. The result updates as you edit the inputs.
Sources & references
- NIST Guide to the SI — National Institute of Standards and Technology
