Heat Transfer Calculator
Calculate heat flow through walls and materials using a U-value or thermal conductivity.
Estimates are based on steady-state formulas. Real-world heat transfer involves radiation, convection coefficients, thermal bridges, and moisture effects. Verify designs with a qualified engineer and applicable building codes.
How it works
- 1Choose a method — overall U-value (Q = U·A·ΔT) or conduction (Q = k·A·ΔT/d).
- 2Enter the area and temperature difference, plus the U-value or conductivity and thickness.
- 3The calculator returns the heat transfer rate in watts, kilowatts, and BTU/h.
Use cases
- Estimating winter heat loss through a wall, roof, or window from published U-values.
- Sizing a heating or cooling system by summing heat flows across the envelope.
- Comparing materials by varying conductivity k and thickness.
Frequently asked questions
What is the U-value method?
Q = U·A·ΔT uses the U-value (W/m²·K), which already includes all resistances in a composite assembly. A wall with U = 0.3, area 50 m², ΔT = 20 °C loses 300 W.
When should I use the conduction method?
Use Q = k·A·ΔT/d when you know the material’s conductivity k and thickness d. 10 cm of mineral wool (k ≈ 0.04) over 10 m² at ΔT = 20 °C gives 80 W.
How do unit conversions work?
Area toggles m²/ft², ΔT toggles Δ°C/Δ°F (1 Δ°F ≈ 0.556 Δ°C), and thickness cm/in. U-value and k are entered in SI (W/m²·K, W/m·K).
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