Electric heaters are usually 100% efficient at converting the electricity to heat in the room where they are located. An electric furnace heats air moved by its fan over several electric-resistance heating elements. Electric heaters have three to six elements – 3.5 to 7 kW each – that work like the elements in a toaster. The 24-volt thermostat circuit energizes devices called sequencers that bring the 24-volt heating elements on, in stages, when the thermostat calls for heat. The multiple speed fan switches to a higher speed as more elements engage to keep the air temperature stable.
While electric furnaces are 100% efficient, they often suffer large heat losses due to duct leakage. Duct leakage can be responsible for wasting up to 30% of electricity used by the furnace. Many electric furnaces have been replaced by fuel-burning furnaces because the electricity is more expensive.
Replacing air filters regularly is vital to the efficient operation of electric furnaces. The electric heating heating elements should be dusted and vacuumed if they get dirty. Cleaning the heating elements should not be necessary if the air filters are changed regularly.
Electric furnaces can be a problem for utility companies if they are using more 5-kW heating elements than are necessary to heat the home – the utility company has a higher peak demand than it would if only the minimum number of elements were used. During mild weather in most climates, only a couple elements are needed. As the temperature gets lower, the other elements become necessary.
Krigger, John, and Chris Dorsi. “Chapter 6 Heating.” Residential Energy: Cost Savings and Comfort for Existing Buildings. Ed. Mary Coster and Margaret Regan. 5th ed. Helena, MT: Saturn Resource Management, 2009. 176-77. Print.