Heat Conduction Calculator
How much heat flows through a wall or window?
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Heat Conduction Calculator by TheCalcTools
How the Heat Conduction Calculator works
Enter the material’s conductivity, the area, the thickness and the temperature difference across it.
Heat flow is proportional to area and temperature difference and inversely proportional to thickness.
The U-value and R-value measure the insulating performance.
The formula
Worked example
Using the default values shown in the calculator:
| Thermal conductivity (W/m·K) | 0.04 |
|---|---|
| Area (m²) | 20 |
| Thickness (m) | 0.1 |
| Temperature difference (K) | 20 |
- U = 0.04 ÷ 0.1 = 0.40 W/m²K.
- Q = 0.04 × 20 × 20 ÷ 0.1 = 160 W.
- Over a day that is 3.84 kWh.
Result:
| Heat flow (W) | 160.0 |
|---|---|
| U-value (W/m²K) | 0.400 |
| R-value (m²K/W) | 2.500 |
| Energy lost per day (kWh) | 3.84 |
Frequently asked questions
What is a good conductivity for insulation?
Mineral wool and foam boards are about 0.03–0.04 W/m·K. Brick is about 0.7 and concrete about 1.4.
Does this cover convection and radiation?
No. It models conduction only. Real walls also lose heat from surface air films and radiation.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.