Radiation Heat Transfer Calculator

Calculate radiative heat exchange using the Stefan-Boltzmann law.

About Radiation Heat Transfer Calculator

Radiation scales with the fourth power of absolute temperature, so it is negligible at room temperature and dominant at high temperatures. Temperatures must be in kelvin for the fourth-power term to work. Above about 400 °C radiation exceeds convection, which is why furnace and turbine design is radiation-dominated.

Formula

Radiation Heat Transfer

Q̇ = ε σ A (T_s⁴ − T_sur⁴), with temperatures in kelvin

ε: Emissivity, 1 for a black body
σ: Stefan-Boltzmann constant, 5.67 × 10⁻⁸

Worked example

With the default values below, Radiation Heat Transfer Calculator returns Radiative Heat Loss of 4,361.622. Change any input above and every figure here is recalculated in your browser.

Inputs used

Surface emissivityaccepts 0.01–1: 0.9
Surface areaminimum 0 m2: 2 m2
Surface temperatureminimum -273 C: 200 C
Surrounding temperatureminimum -273 C: 20 C

Results

Radiative Heat Loss: 4,361.622 W
Radiative Heat Flux: 2,180.811 W/m2
Surface Temperature: 473.15 K
Equivalent Radiative Coefficient: 12.1156 W/m2 K
Annual Energy Radiated: 38,207.8 kWh

Step by step

1Values used
2Radiation Heat Transfer
3Radiative Heat Loss= 4,361.622 W
4Radiative Heat Flux= 2,180.811 W/m2
5Surface Temperature= 473.15 K
6Equivalent Radiative Coefficient= 12.1156 W/m2 K
7Annual Energy Radiated= 38,207.8 kWh

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Radiation Heat Transfer calculated?

Q̇ = ε σ A (T_s⁴ − T_sur⁴), with temperatures in kelvin Radiation scales with the fourth power of absolute temperature, so it is negligible at room temperature and dominant at high temperatures. Temperatures must be in kelvin for the fourth-power term to work.

Why does Radiation Heat Transfer matter?

Above about 400 °C radiation exceeds convection, which is why furnace and turbine design is radiation-dominated.

What values do I need to enter?

This calculator takes 4 inputs: Surface emissivity, Surface area, Surface temperature, Surrounding temperature. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.