It is a common practice to run the furnace fan continuously at low speed to improve the comfort of residents. In many parts of Canada, homeowners often install central air-conditioning systems that utilize the furnace blower. However, a constantly running fan dramatically increases annual electrical consumption by the furnace beyond levels consumed by the traditional demand-only mode of operation during the heating season.
The standard type of alternating current (AC) motor used in most furnaces – the four-speed permanent split capacitor (PSC) type – is not the most energy efficient, particularly when operated at low speeds. Many furnaces now use high-efficiency, variable-speed, brushless direct current (DC) motors. When used continuously, a high-efficiency motor uses less than one third of the electricity consumed by a standard motor and eventually pays for itself in reduced electrical bills.
The electrical savings from a furnace equipped with a high-efficiency motor will be offset somewhat by the extra heat that the furnace must supply. However, when central air conditioning is used, the high-efficiency fan-blower motor will provide additional savings since the heat from the inefficient motor no longer needs to be cooled.