How to Calculate Heat Dissipation in Electrical Enclosures

Overheating is a common reason many electrical devices fail and become unusable, but this can be prevented when an enclosure can effectively dissipate its internal heat. The heat dissipation rate is dependent upon the enclosure's size, wattage, and external ambient temperature. If the ambient temperature becomes higher than the enclosure's ambient temperature, heat can no longer be dissipated and can cause damage. Calculating an electrical enclosure's heat dissipation rate is the first step to prolonging the life of your electrical components. Use the following information to calculate input power and temperature rise and determine the heat dissipation rate.

NEMA Enclosure Type 3 3R Junction Box
NEMA Enclosure Type 12 Junction Box
NEMA Enclosure Type 1 Junction Box
NEMA Enclosure Type 4 Junction Box

How to Find Temperature Rise

Temperature rise is the difference in temperature between the air inside a sealed enclosure and the ambient air surrounding it. Once the temperature rise is known, add it to the ambient temperature to find the maximum service temperature.

First, calculate the surface area of the enclosure using the formula:

Surface Area = 2 x ((height x length) + (height x width) + (length x width)) / 144

Note: length, width, and height are measured in inches

Second, determine the input power by dividing the heat dissipated in the enclosure (watts) by the enclosure surface area using the formula:

Input Power = watts/ft2

Finally, use the Temperature Rise graph below to find the approximate input power on the X‑axis, then move up the Y‑axis until the input power intersects the temperature rise curve.

Chart Graph Guide: Heat Dissipation Correlation to Input Power


Find the expected temperature rise from a 48″ x 36″ x 16″ electric enclosure with 300 watts of heat dissipated.

Calculate Surface Area: 2 x ((48 x 36) + (48 x 16) + (36 x 16)) / 144 = 42 ft2

Determine Input Power: 300 watts / 42 ft2 = 7.1 watts/ft2

Use the graph to find the Temperature Rise

Locate the calculated input power on the bottom X‑axis. Move directly up the Y‑axis and meet the diagonal curve line to find the approximate temperature rise.

Temperature Rise = 30°F (16.7°C)

Chart Graph Guide: Heat Dissipation Correlation to Input Power

Enclosure Types

Non-Metal Enclosures

Non Metal Fiberglass Enclosure

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Steel Enclosures

Junction Box, Steel, Type 4 Continuous Hinge

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Explosion-Proof Enclosures

Nema 7 Explosion proof Enclosure

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Warning: When using this information to perform electrical work, call a licensed electrician and consult the NEC® for safety. All licensed electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.