There are 6 main types of furnaces. They are Gas Furnace, Electric Furnace, Oil Furnace, forced-air, hot water, steam/radiant floor.
Gas furnaces produce hot air circulated through ductwork to warm your home. Some of the most efficient gas furnaces are 95 percent AFUE rated, which means they can convert up to 95 percent of their input fuel into heat energy. Gas furnaces are available in single-stage or two-stage models.
Electric furnaces are generally used for small, supplemental heating applications such as additions, garages, and sunrooms. They do not require ductwork.
Oil furnaces are used for space heating in some parts of the country, but overall they have declined in popularity due to advances in other furnace types. This system is a prime example of a "comfort" appliance as it is often difficult to control temperature and hot air tends to stratify near the ceiling.
The forced air furnace is the most common type of furnace in use today. It recovers heat from the flue gases then transfers it throughout the home through a series of ducts. Forced-air furnaces are available as hot-surface, modulating, or two-stage furnaces.
Hot water heating systems are typically found in single-family homes but can also be found in larger buildings. Water is heated by the furnace and circulated through piping to radiators or convectors throughout the house, where heat is released into the air. Hot water furnaces are available as storage or demand types.
Steam heating systems are standard in larger buildings but can also be found in smaller commercial applications. Heat is transferred to the surrounding air by steam or hot water radiators attached to the wall. Radiant floor heat is also used for forced-air space conditioning. This system uses hot water pipes installed under the floor, which heats the surrounding air.
Steam heating systems are available as low-pressure or high-pressure types. These systems are suitable for large buildings with many radiators because they provide even heat distribution.
