There are two big parts to how a gas furnace works. First of all, there is the heat exchanger and secondly there is a blower fan motor.
What happens when the thermostat calls for heat and the furnace turns on?
Well the furnace will in fact fire itself on and begin to heat up the heat exchanger. It then draws in (vacuums) air in through the return air inlets, or commonly called the cold air returns.
The cold, unconditioned air is then vacuumed into the furnace and is passed through an air filter. The blower fan motor, which is at the bottom of the furnace then pushes the air up through a heat exchanger. Most furnaces are what is called an updraft furnace such as what I am referring to here.
For lack of a better term, the heat exchanger is a great big metal chamber, or series of chambers, that holds the fire, the combustion. Whether you’re dealing with a natural gas furnace and oil furnace, a propane furnace, as that air passes by the heat exchanger the air warms up. In the case of an electric furnace the heat exchanger is actually a series of electric tubes. These tubes heat up and glow red when activated… much like your toaster does at home.
So what actually happens is that cool air passes by that hot steel (or glowing red tubes), it warms up the air and then hot air is distributed throughout the house.
What does the blower fan motor do?
The blower fan motor is located down near the bottom of the furnace, regardless of what energy the furnace actually uses. The blower fan motor is what drives all the air in the house… or is responsible for the entire convection of air. All the air that is supplied and all the air that is returned or vacuumed in. If you think about all the air that’s coming out of the supply registers in your kitchen or your recreation room, and all the air that’s being drawn into the return air inlets in your family room and bedrooms… All of that air is being driven by the blower fan motor.
Now… Not only does the blower fan motor play an important role when heating your house, but it is equally important when cooling your house. If you have a central air conditioner in your house, then the blower fan motor is responsible for vacuuming in warm air, running it past the past the evaporator coil, and in turn removing the heat from the air.
When that heat is removed from the air, naturally the temperature of the air drops. When the temperature falls, then the humidity (or vapor) that was in the air simply falls out of the air. The air temperature has reached it’s dew point , and has been de-humidified. The end result is that nice cool, dry air is distributed throughout the house.
And if the blower fan motor is a good, powerful motor (such as a DC motor), then it will deliver the proper temperatures to our house. Whether we’re heating or whether we’re cooling, a blower fan motor is definitely an important part of a furnace. That is a how a gas furnace works.
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