Radiative Heat Transfer Calculator

Estimate net thermal radiation, heat flux and a constant-condition energy total for one surface and its surroundings.

This first-pass model assumes the stated effective view factor and a uniform surroundings temperature.

Net radiative heat transfer416.874 W1,422.434 Btu/h
Net radiative heat flux416.874 W/m²Surface: 353.2 K · surroundings: 293.2 K
Energy over stated duration0.417 kWh1,422.434 Btu

Interpretation: a positive result is net heat emitted by the surface; a negative result is net radiative heat absorbed by it. The duration result assumes constant temperatures, emissivity and view factor. Emissivity can vary substantially with material finish, oxidation, wavelength and temperature.

Method

For a surface that effectively views uniform surroundings, Q̇ = ε × F × σ × A × (Ts4 − Tsur4). Temperatures must be absolute temperatures, so the calculator converts °C and °F to kelvin before applying the fourth-power relation.

Worked example

A 1 m² surface at 80 °C with ε = 0.9 and F = 1 facing 20 °C surroundings emits roughly 417 W of net thermal radiation under this simplified model. At the same conditions for one hour, that is about 0.417 kWh.

Important limits

This calculator is a first-pass enclosure model. It does not account for multiple surfaces, reflected radiation, participating gases, convection or conductive heat paths. Use a radiation-network method for an enclosure with several effective surfaces or a detailed view-factor analysis.

Frequently asked questions

What radiation equation does this calculator use?

It uses Q̇ = ε × F × σ × A × (Ts⁴ − Tsur⁴), where ε is emissivity, F is the effective view factor and σ is the Stefan-Boltzmann constant. Temperatures are converted to kelvin before the equation is applied.

When should the effective view factor be 1?

Use 1 when the whole emitting surface effectively sees the stated large uniform enclosure. For smaller targets or several facing surfaces, use a radiation-network method rather than treating the view factor as a complete geometry model.

Why can the result be negative?

A negative result means the surface is cooler than the stated surroundings, so it absorbs more thermal radiation than it emits. It does not mean the calculation has failed.

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Convective Heat Transfer Calculator · Heat Loss Calculator · Heat Transfer Calculators