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How a Forced-Air HVAC System Works

Central forced-air heating systems are by far the most popular method of heating homes in North America, no doubt because they can deliver heated air from a central furnace or heat pump to every room of the house and because it can double-up for delivery of air-conditioned air.

The basic components of a forced-air system include:

1) An air handler, which may be either a stand-alone blower cabinet used with a heat pump or a forced-air furnace that includes a blower

2) A means of heating air, such as gas-fueled burners or electric-resistance heating elements

3) Ductwork for delivering room air to the heater


4) Ductwork for sending heated air back to rooms

5) A thermostat for turning the system on and off

Of course, forced-air systems include a few other parts and pieces that refine their work, including filters to clean the air, registers to direct and control the flow of air to rooms and, in the case of heaters that utilize combustion for heat, a flue for venting combustion gasses outdoors.

When the thermostat tells the system that room temperatures are below a set comfort level, the air handler kicks on, drawing room air from a “cold air return” through ductwork into the furnace’s heat exchanger, a metal chamber around which air flows.


The burners or electric heating elements turn on or the heat pump engages to heat the air as it moves through the air handler.

The blower then forces the warmed air through a network of ductwork back to the rooms. And the cycle continues until the set comfort level is reached and the thermostat turns the system off.

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