All forced hot air furnaces are equipped with a furnace blower that works to circulate hot air throughout the house. A home heater, or furnace, that uses forced hot air consists of the burner, the plenum, and the furnace blower. In the typical forced hot air system, the burner is fired by oil, natural gas, or wood. Air that is heated by the burner is gathered in the plenum. The hot air is then forced, or blown, from the plenum throughout the house by the furnace blower.
The furnace blower is the primary factor that differentiates a forced hot air system from forced hot water or steam heaters. Forced hot water heating systems have a pump to deliver water, heated by the burner, to the different rooms. Steam heating systems use the expanding nature of the steam, again heated by the burner, to deliver heat to the radiators throughout the house. Forced hot air has the advantage of being the fastest delivery of heat, but is also somewhat less clean and, due to the possibility of carbon monoxide buildup, marginally more dangerous system.
Another method of home heating is electric heat. An electric heating system delivers heat, without the need for a burner or furnace blower, through the electrically heated loops in each room of the house.
Typical home heaters, whether steam, forced hot air, forced hot water, or electric, operate in essentially the same fashion. An adjustable thermostat, usually positioned near the center of the home, senses the temperature inside the home. It then sends an electrical impulse to the heater burner which ignites and the heat is expanded, blown, pumped, or electrically delivered throughout the home.
Once the thermostat senses that the temperature in the home has reached its pre-set level, it sends another impulse to the burner to shut off. Ordinarily, in a forced hot air system, the furnace blower will continue to operate for another minute or two, forcing the last of the heated air from the plenum into the home, and then shuts down.
A furnace blower is, ordinarily, the part of the heating system that works the hardest, thus is the part most frequently repaired or replaced. An electric motor and a fan are often the sole furnace parts that are moving during the heating process. In older furnaces, the fan is usually belt-driven, while newer furnaces use a belt-less centrifugal fan.
Repair and replacement of a furnace blower can often be accomplished by the average homeowner. The repair usually involves replacement of motor bearings and drive belts in older furnace blowers, and just the bearings in centrifugal blowers.