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Radiation Heat Transfer Calculator

Estimate net thermal radiation heat transfer and equivalent linearized radiation coefficient with absolute-temperature handling.

Radiation Heat Transfer inputs

Result section

warningheat-rate

Net radiation heat-transfer rate

8434.68 W

Secondary results

Radiation heat flux: 843.468 W/m^2
Linearized radiation coefficient: 8.43468 W/(m^2·K)
Heat-flow interpretation: Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

Unit conversion summary

Unit-normalization summary: SI base units; heat-rate

Warnings

Thermal properties can vary with temperature, pressure, composition, grade, direction, phase, surface condition, manufacturing process, and data source. Verify all values for the actual operating condition.

Assumptions

Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Calculation steps

Convert temperatures to kelvin and apply Stefan-Boltzmann law8434.68 W

Surface-to-surroundings radiation

Qdot = epsilon sigma A F (Ts^4 - Tsur^4)

Technical visual

Calculate radiation heat transfer from emissivity, area, view factor, and absolute temperatures.

Engineering interpretation

Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

What is the radiation heat transfer calculator?

Use this calculator for simplified gray diffuse surface-to-surroundings radiation estimates when absolute temperatures are known.

How to use the radiation heat transfer calculator

Enter surface and surroundings temperatures as absolute-temperature inputs such as C, F, K, or R.
Enter emissivity and view factor between 0 and 1.
Review net heat direction and the linearized coefficient if needed for resistance models.

Input explanations

Radiation formulas use absolute temperature internally, so Celsius and Fahrenheit inputs are converted to kelvin.
Emissivity and view factor are dimensionless inputs between 0 and 1.
The linearized coefficient is valid around the entered temperature pair.

Notation

Formula notation
Symbol	Meaning	Unit
epsilon	Surface emissivity	-
sigma	Stefan-Boltzmann constant	W/(m2 K4)
F	View factor	-
Ts, Tsur	Absolute temperatures	K

Worked examples

For epsilon = 0.8, A = 2 m2, Ts = 400 K, and Tsur = 300 K, net radiation is about 1587.7 W.

Cross-tool workflow

The radiation calculator applies the Stefan-Boltzmann surface-to-surroundings relationship with emissivity, view factor, and absolute temperatures.

Use equivalent h in resistance model

Common mistakes

Using Celsius values directly in T to the fourth power.
Assuming view factor is 1 for partial enclosure geometries.
Using polished-surface emissivity for oxidized or rough surfaces.

Limitations

Thermal properties are treated as constant user-entered values.
The tool does not select material, fluid, steam, refrigerant, phase-change, or fouling data automatically.
Results are preliminary engineering estimates and do not certify code compliance or safety.
Multidimensional effects, transient storage, contact details, and property variation must be evaluated separately when important.
Assumes gray diffuse surface behavior and a user-entered view factor.
Does not solve radiation enclosure networks or spectral radiation.

References

Fundamentals of Heat and Mass Transfer: Incropera, DeWitt, Bergman, and Lavine, Fundamentals of Heat and Mass Transfer.
Heat and Mass Transfer: Cengel and Ghajar, Heat and Mass Transfer: Fundamentals and Applications.
Heat Transfer: Holman, Heat Transfer.
Compact Heat Exchangers: Kays and London, Compact Heat Exchangers.
SI units: BIPM, The International System of Units (SI Brochure).
NIST unit guidance: NIST Special Publication 811, Guide for the Use of the International System of Units.

What assumptions does the radiation heat-transfer calculator use?

It uses the stated steady or lumped formula with user-entered properties and does not infer hidden losses, standards factors, or temperature-dependent property data.

Are Celsius and Fahrenheit temperature differences handled as offsets?

No. Absolute temperature and temperature difference are separate quantities. Temperature differences use delta units without absolute-temperature offsets.

Can I use the result for final design approval?

No. Use the result for education, estimation, and preliminary review only. Critical work must be checked with standards, validated software, measured properties, and qualified engineering judgment.

Does the calculation run on a remote thermal-property API?

No. Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Engineering disclaimer

This tool is intended for educational, estimation, and preliminary engineering use. Always verify critical heat-transfer calculations with applicable standards, validated software, measured properties, and qualified professional judgment before using results in real design, manufacturing, construction, safety, or compliance decisions.

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Last reviewed: 2026-06-30

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Radiation Heat Transfer inputs

Result section

warningheat-rate

Net radiation heat-transfer rate

8434.68 W

Secondary results

Radiation heat flux: 843.468 W/m^2
Linearized radiation coefficient: 8.43468 W/(m^2·K)
Heat-flow interpretation: Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

Unit conversion summary

Unit-normalization summary: SI base units; heat-rate

Warnings

Thermal properties can vary with temperature, pressure, composition, grade, direction, phase, surface condition, manufacturing process, and data source. Verify all values for the actual operating condition.

Assumptions

Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Calculation steps

Convert temperatures to kelvin and apply Stefan-Boltzmann law8434.68 W

Surface-to-surroundings radiation

Qdot = epsilon sigma A F (Ts^4 - Tsur^4)

Symbol

Meaning

Unit

epsilon

Surface emissivity

sigma

Stefan-Boltzmann constant

W/(m2 K4)

View factor

Ts, Tsur

Absolute temperatures

Limitations

Thermal properties are treated as constant user-entered values.

The tool does not select material, fluid, steam, refrigerant, phase-change, or fouling data automatically.

Results are preliminary engineering estimates and do not certify code compliance or safety.

Multidimensional effects, transient storage, contact details, and property variation must be evaluated separately when important.

Assumes gray diffuse surface behavior and a user-entered view factor.

Does not solve radiation enclosure networks or spectral radiation.

References

Fundamentals of Heat and Mass Transfer: Incropera, DeWitt, Bergman, and Lavine, Fundamentals of Heat and Mass Transfer.

Heat and Mass Transfer: Cengel and Ghajar, Heat and Mass Transfer: Fundamentals and Applications.

Heat Transfer: Holman, Heat Transfer.

Compact Heat Exchangers: Kays and London, Compact Heat Exchangers.

SI units: BIPM, The International System of Units (SI Brochure).

NIST unit guidance: NIST Special Publication 811, Guide for the Use of the International System of Units.

Engineering disclaimer

Radiation Heat Transfer inputs

Calculation mode

Radiation inputs

Result section

Secondary results

Unit conversion summary

Warnings

Assumptions

Calculation steps

Surface-to-surroundings radiation

Technical visual

Engineering interpretation

What is the radiation heat transfer calculator?

How to use the radiation heat transfer calculator

Input explanations

Notation

Worked examples

Cross-tool workflow

Common mistakes

Limitations

References

Related tools

Print summary

Engineering disclaimer

Need Professional Support?

Radiation Heat Transfer inputs

Calculation mode

Radiation inputs

Result section

Secondary results

Unit conversion summary

Warnings

Assumptions

Calculation steps

Surface-to-surroundings radiation

Technical visual

Engineering interpretation

What is the radiation heat transfer calculator?

How to use the radiation heat transfer calculator

Input explanations

Notation

Worked examples

Cross-tool workflow

Common mistakes

Limitations

References

Related tools

Print summary

Engineering disclaimer

Need Professional Support?