Furnace (central heating)

Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water.

These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel.

Air circulation depended on large, upwardly pitched pipes constructed of wood or metal.

Furnaces that used solid fuels required daily maintenance to remove ash and "clinkers" that accumulated in the bottom of the burner area.

In later years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home.

The second category of furnace is the forced-air having atmospheric burner style with a cast-iron or sectional steel heat exchanger.

Through the 1950s and 1960s, this style of furnace was used to replace the big, natural draft systems, and was sometimes installed on the existing gravity duct work.

The heated air was moved by blowers which were belted driven and designed for a wide range of speeds.

This style furnace still used large, masonry or brick chimneys for flues and was eventually designed to accommodate air-conditioning systems.

The draft inducer allows for the exhaust piping to be routed vertically or horizontally as it exits the structure.

Normally the fresh combustion air is routed alongside the exhaust PVC during installation and the pipes exit through a sidewall of the home in the same location.

However, the simplicity of single-stage gas furnaces come at the cost of blower motor noise and mechanical inefficiency.

One major advantage of this type of system is that it also enables easy installation of central air conditioning, simply by adding a cooling coil at the outlet of the furnace.

Air is circulated through ductwork, which may be made of sheet metal or plastic "flex" duct, and is insulated or uninsulated.