Recommended Breaker Size for an Electric Furnace

Homes throughout the United States are either heated through a furnace or boiler. Electric furnaces work by heating air and distributing air throughout your home through air ducts. As with any other electric appliance, an electric furnace must be connected to a circuit breaker. If you are interested in purchasing and installing an electric furnace you should use an appropriately sized breaker.

Home boiler and water heater
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Electric furnaces require different breaker sizes based on electric output.

Referring to Owner’s Manual

The most foolproof way to determine the recommended breaker size for an electric furnace is to refer to its owner's manual. Most manuals will describe in detail the recommended breaker size, and provide you with a list of suggested breakers. If the manual does not offer this information, directly contact the manufacturer to obtain breaker size recommendations.

Breaker Size Based on Wattage

The size of a breaker is determined by the amp draw. The exact amps an electric furnace requires is solely based on the size of the furnace and its performance capabilities; however, typically electric furnaces require a draw between 60 and 80 amps. By multiplying the volts by amps you will receive total wattage. The average American household uses 220 volts for larger appliances; however, the actual voltage can vary from 120 to 254. While the exact formula used to determine overall wattage will vary based on your voltage system, once you discover this information you can find the total wattage used by your furnace, and with this total you may install the proper breaker size. For example, 220 volts multiplied by 80 amps equals a total wattage of 17,600. With this wattage a 100 amp breaker may be ideal.

Sizing Your Electric Furnace

While shopping for an electric furnace you must determine the British thermal unit output necessary to heat your entire home. Electric furnaces are sold in 10,000 to 15,000 BTU increments. It takes roughly 25 to 30 BTU's to heat one square foot in a warm climate, 35 to 40 BTU's to heat one square foot in a cold climate and 45 BTU's to heat one square foot in a frigid climate. Using this formula, a 2,500-square foot home in a cold climate requires anywhere from 75,000 to 100,000 BTU's to adequately heat the entire house. By determining the required BTU's you will ensure you have a large enough electric furnace and a large enough breaker to sustain the furnace's electricity requirements.

Warnings

Do not attempt to configure a breaker size if you are not well-versed in circuit breakers and electrical wiring. By installing an improper breaker size, you risk damaging the furnace and potentially causing extensive damage to the electrical system within your home.