What is Radiation Heat Transfer?

Radiation heat transfer is the process by which thermal energy is exchanged between surfaces through electromagnetic waves. Unlike conduction and convection, radiation does not require a physical medium to travel, meaning it can transfer heat through a vacuum. This is how the sun's energy reaches the Earth.

The amount of heat radiated depends on the surface temperature, the surface area, and the emissivity of the material. The fundamental principle governing this is the Stefan-Boltzmann Law, which states that the total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature.

How to Use the Radiation Heat Transfer Calculator

Using our online tool is simple and designed for engineers, students, and HVAC professionals:

• Emissivity (ε): Enter a value between 0 and 1. A perfect blackbody has an emissivity of 1.0, while polished metals might be as low as 0.05.
• Surface Area: Enter the area of the object emitting radiation in square meters (m²).
• Temperatures: Enter the hot surface temperature and the surrounding ambient temperature. You can select between Celsius, Kelvin, or Fahrenheit.
• Calculation: Click "Calculate" to find the net heat transfer rate in Watts (W).

The Stefan-Boltzmann Equation

The calculator uses the standard formula for net radiation exchange between a grey body and its surroundings:

Q = ε · σ · A · (T₁⁴ - T₂⁴)

Where:
Q = Net heat transfer rate (Watts)
ε = Emissivity of the object
σ = Stefan-Boltzmann constant (5.670373 × 10⁻⁸ W/m²·K⁴)
A = Surface area (m²)
T₁ = Absolute temperature of the hot body (Kelvin)
T₂ = Absolute temperature of the surroundings (Kelvin)

Frequently Asked Questions