How Does Your Forced Air Gas Furnace Work?

Forced Air Gas Furnaces are the most effective way to circulate warm air throughout your home and maintain a consistent temperature throughout your space.  Other options, such as electric baseboard heaters, tend to heat individual areas, creating hot and cold zones within your home, and are usually less cost efficient to operate.  Gas furnaces operate by monitoring the temperature of your indoor air, and circulating warm air throughout the home via ductwork, as needed.


It all begins with the thermostat, which is set to a temperature of your choosing.  Once the heat drops below that level, the furnace becomes engaged and the heating process begins.

Combustion Chamber

A pilot light or silicon nitride starter acts as an ignition source for the gas, in order to generate heat.  Air and gas combine inside a combustion chamber and, once ignited, burn long enough to heat the cold air inside the heat exchanger.

Heat Exchanger

The heat exchanger holds the warming air until it reaches the required temperature, at which time the blower is turned on.  The blower sends the warmed air throughout the home’s duct work system, and ultimately, into any room where a heat register is open.  Once the thermostat registers that the heat level in the home has met its programmed temperature, the blower turns off and the air no longer circulates through the ducts.

Cold Air Return

As the warm air circulates through the space, it expels the existing cold air in the room.  This cold air is then collected via the cold air return vents and sent back to the furnace.  Filters clean any dust and allergens from the air and return it to the plenum, until the air is needed for the next heating cycle.

Flue Pipe

Although very little by product remains after combustion, there are still residual harmful gases that do not get burned off during the course of the heating cycle.  A flue pipe is necessary for venting purposes, in order to direct any potentially dangerous gases outside of the home.

High-efficiency Furnaces

High efficiency gas furnaces have an extra combustion chamber.  Unused gases are collected and burned for a second time in order to burn gases almost completely.  A venting system is still required to remove any unburned gas from the home, but it is a much more efficient and cost effective system since considerably less gas is used to heat the home.