Control Panel Heat and Fan Sizing Calculator

Add up the heat inside a control panel and find the fan airflow needed to keep the inside temperature within your limit.

Temperature limits

Use the lowest maximum operating temperature of any device in the panel, and the hottest ambient the panel will see. Enter both in the unit chosen. The defaults are 104 °F (40 °C) inside and 86 °F (30 °C) outside.

Heat sources (name, quantity, watts)

Use each device's heat dissipation (watts of loss), not its power rating. The datasheet lists it. Include everything inside the enclosure.

Pick a fan with margin. The result is the airflow needed in free air. A filter, grille or dirty filter reduces the real airflow, so choose a fan rated well above the figure and check its flow curve against the pressure drop of the filter. Also ensure the intake air is the ambient air and not warmer, and keep dust out of the enclosure if its rating requires it.

How it works

The fan has to carry away the heat generated inside the panel with air that is allowed to be a certain amount warmer than the outside air. The heat needed to warm air by one degree Fahrenheit is about 1.08 BTU per hour for each cubic foot per minute, and one watt is 3.412 BTU per hour. Combining those gives the airflow formula:

CFM = 3.16 × watts ÷ temperature rise in °F
m³/h = CFM × 1.699

Worked example

The sample panel gives off 90 + 50 + 30 + 15 = 185 W. With 104 °F allowed inside and 86 °F outside, the rise is 18 °F. The airflow needed is 3.16 × 185 ÷ 18 = 32 CFM, about 55 m³/h.

Common questions

Do I always need a fan?

Not always. A panel with little heat in a cool place may lose enough heat through its walls, but this calculator does not estimate that. If the allowed rise is small or the heat is large, a fan, heat exchanger or air conditioner may be needed. Enclosure makers publish heat dissipation data for their enclosures.

What about a sealed (NEMA 4 or IP65) panel?

A fan that draws in outside air breaks the seal. Sealed panels usually use a heat exchanger or an air conditioner, which are sized from the same total heat load.

Calculations are provided for convenience and education. Check device datasheets and the enclosure manufacturer's thermal data before finalizing a design.