Furnaces: Types, selection and repair & maintenance
What is a Furnace, How it Works and How to Keep Yours Working Right.
What is a furnace? Simply put, a furnace draws air in from the living space, heats it up and returns it to warm the home. Modern furnaces are forced air systems in three basic configurations based on the direction in which the furnace outputs heat:
An upflow furnace takes cool air in from the bottom and discharges it from the top. Upflow furnaces are generally placed in a home's basement.
A gravity furnace is a type of upflow furnace that does not use a blower motor, but instead using physics - the heated air rises through ducts and cooled air sinks through return vents. Gravity furnaces are incredibly efficient but don’t provide the immediate gratification of blower units.
Horizontal flow (or cross-flow) furnaces
A horizontal furnace lies on its side, pulling cool air from one side and pushing warm air out of the other.
Horizontal furnaces are often used in locations where there is limited space and may be found in a crawl space or a closet.
In this configuration, the furnace takes cool air from the top and discharges warm air from the bottom.
Downflow furnaces are generally found in homes with no basement and are usually placed in an attic.
Choosing a Furnace Configuration. The biggest consideration in choosing among these configurations is your home's layout. If you have no basement or crawlspace, an upflow furnace is not an option.
Because hot air naturally rises and cold air sinks, upflow furnaces have to perform less work and tend to have longer life spans than the other configurations.
The hot air in an upflow furnace will dissipate its stored air quickly because the air rises out of the unit on its own, whereas in horizontal flow and downflow furnaces, the unit doesn't cool down as fast so they incur more wear. That’s something to think about if you’re building a new home. Another thing to consider is the heat source.
Furnace Fuel Options. Most furnaces use gas—either natural gas or propane. The gas enters a chamber, is ignited by the pilot and warms the air within a heat exchange chamber. The air is blown into the living space through heating ductwork and the exhaust gases are vented out of the home. Electric furnaces use heating elements, or strips, to warm the air instead of a fossil fuel source. Everything else works the same way.
Furnace Maintenance. As with all HVAC systems, at some point furnace repairs will be necessary. To help extend the life of your furnace be sure to provide regular maintenance. For example, air filtration is critical to effective heating, so you should make sure to change or clean your furnace filters often and have your furnace professionally serviced before every heating season.
Contact your local ARS®/Rescue Rooter® heating and air conditioning specialist for your furnace repair and maintenance needs or to find out what type of furnace best fits your home.