Air conditioners and furnaces ⏤ how do they work together?

Air conditioners and furnaces work together to keep the air in your home at a manageable temperature. In the winter, your furnace heats the air in your home, while the AC blower circulates works to circulate that air throughout the home.

In the summer, your AC takes a more prominent role, removing heat and humidity from the home. As your AC works to cool the air, the evaporator coil within the unit controls the hot air created during the refrigeration process and expels it outside where it can dissipate. 

What is a furnace?

Most North American homes are kept warm with furnaces, of which there are 3 main types: natural gas, oil and electric. There are also non-furnace home heating solutions, such as heat pumps and steam heat boilers, which interact with HVAC systems in ways similar to furnaces. Some homes may also have zone heating systems like baseboard heaters, radiant floor heating or wood burning stoves.

How do home furnaces work?

Furnaces vary in the types of energy they consume, which affects how they produce heat. But once a furnace creates warm air, it gets distributed the same way, regardless of the energy type. How does a furnace work in a house? Here are the basic steps:

1. When the temperature in the house drops below the thermostat setting for heat, the thermostat sends 2 signals: one to the furnace to begin a heating cycle, and another to the blower motor to activate the HVAC fan.
2. The furnace’s heating elements receive the signal and activate. In gas and oil furnaces, those fuels are released through valves to produce open flames. In electric furnaces, electricity powers heating elements that are like large versions of the elements in electric space heaters.
3. The heat is transferred to the air. In electric furnaces, this is simply a matter of the exposure of the heating elements to the open air. In gas and oil furnaces, the flames heat a component called the heat exchanger, a sealed chamber that warms the air around it.
4. The blower motor and fan push the warm air through the ductwork and vents, raising the temperature in the home.
5. The thermostat detects the moment when the indoor temperature reaches the desired level and sends signals to shut off the furnace and blower motor.

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