Heat Transfer Calculator
Works out the rate of heat flow by each of the three ways.
Heat flow rate
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Heat flux — W/m²
Energy per day — kWh
Reading this —
The formula
conduction: Q = k A ΔT ÷ d convection: Q = h A ΔT radiation: Q = ε σ A (T₁⁴ − T₂⁴)
σ is the Stefan–Boltzmann constant, and radiation needs absolute temperatures, which are handled here.
What to watch out for
For sizing a home heating system, use the heating calculators, which allow for climate and insulation.
Frequently Asked Questions
How much heat passes through a 10 m² brick wall, 10 cm thick, with a 20 °C difference?
About 1,600 W, with k = 0.8 W/m·K.
How much does a surface at 100 °C radiate?
With emissivity 0.9 into 20 °C surroundings, about 613 W per square metre.