The efficiency of an electric furnace is usually ______ percent.

• A. 100 percent
• B. 10 percent
• C. 80 percent
• D. 50 percent

Answer: (A)

Electric furnaces heat by electrical resistance, turning electrical energy directly into heat. There’s no combustion or exhaust to lose energy, so almost all the input energy ends up as heat in the space you’re warming. When ratings count the energy delivered to the living area (including the heat from the blower), an electric furnace is effectively 100% efficient. The other percentages would imply significant energy is wasted before heating the space, which doesn’t apply to this heating method.