How Your HVAC Systems Work

Your thermostat is the control center of your entire HVAC system. It constantly monitors the temperature in your home and turns on your heating or cooling units according to your preferred setting.

Once your heating or cooling system receives the signal to run, the way it changes the temperature depends on the specific units you have installed:

Heating Units

Furnace: Furnaces are typically installed in a basement, utility room, attic, garage, or crawl space.

1. The system burns fuel (natural gas or oil) or uses electricity to create heat.
2. A metal heat exchanger (or heating elements in an electric furnace) becomes very hot.
3. A blower fan pulls cool air from your home through the return ducts.
4. This air passes over the hot heat exchanger, warming up quickly.
5. The blower pushes the warm air through your ductwork and into each room.

Boiler: Boilers are typically installed in a basement, utility room, or garage. They connect to a network of water or steam pipes.

1. The system burns fuel or uses electricity to heat water or generate steam.
2. A circulator pump moves the hot water or steam through pipes in your home to radiators, baseboard heaters, or underfloor heating.
3. These heating units warm each room through radiant heat, natural convection, or a combination of both.
4. As the water cools, it flows back to the boiler to be reheated.

Heat Pump: Heat pumps do not create heat; they move it from one place to another using a refrigerant loop.

1. The outdoor unit absorbs heat from the outside air using a special fluid called refrigerant. Even when it feels cold, the outdoor air still contains thermal energy.
2. The heat pump compresses the chemical refrigerant, which concentrates the absorbed heat and raises its temperature significantly.
3. An indoor coil transfers this heat from the refrigerant directly to your indoor air.
4. A blower fan pushes the warm air through your ductwork and into each room.

Cooling Units

Central Air Conditioner: Central AC relies on a split system with indoor and outdoor components to cool your entire home.

1. The indoor unit uses cold refrigerant to absorb heat from your indoor air. As the air cools, excess humidity condenses on the coil and is drained away.
2. The refrigerant carries the captured heat to the outdoor unit, where a fan vents it outside.
3. The blower fan pushes the newly cooled, dry air through your ductwork and into your rooms.

Ductless Mini-splits: A mini-split cools individual rooms directly without needing large ductwork.

1. The compact indoor unit is mounted on a wall or ceiling. It connects directly to an outdoor unit through a small refrigerant line.
2. Just like a central air conditioner, it uses refrigerant to absorb heat and moisture from the room.
3. The refrigerant carries the heat to the outdoor unit, where it is released.
4. The indoor unit blows the newly cooled, dry air directly back into the room.

Heat Pump: The same heat pump that keeps you warm in the winter can cool your home in the summer by reversing its process.

1. Instead of pulling heat from the outdoors, it absorbs heat and moisture from your indoor air using refrigerant.
2. The refrigerant carries the indoor heat to the outdoor unit and releases it outside.
3. A blower fan pushes the newly cooled, drier air through your ductwork.

As your system runs, your thermostat or built-in unit sensors constantly monitor your indoor temperature. Once your home reaches your exact setting, the system automatically adjusts to save energy.

It depends on the type, age, and specifics of your units, but most will do one of two things:

1. Completely shut off: Traditional heating and cooling systems turn off entirely once they reach the target temperature. The system goes silent and rests until your home needs another cycle.
2. Scale Down Speed: Modern variable-speed systems do not turn off. Instead, they automatically dial down to a whisper-quiet, low-energy speed. This allows them to run continuously at a fraction of their capacity to keep your comfort level perfect.

Monitors your home's temperature and tells your heating or cooling system when to start and stop. (Can be used with all systems.)

The unit that circulates air. A furnace creates its own heat and blows it through the house. An air handler does not create heat; it simply blows air across indoor coils to circulate heated or cooled air. (Varies by system type.)

Contains refrigerant that absorbs heat from your indoor air. As the air cools, excess humidity is also removed. (Used in central AC and heat pump systems.)

The outdoor unit that releases the heat collected from inside your home. (Used in split, packaged, and air-source heat pump systems.)

Carry refrigerant between the indoor and outdoor units to transfer heat. (Used in AC, heat pump, and mini-split systems.)

Carries heated or cooled air to each room and returns indoor air to the system. (Not used in ductless mini-splits.)

Traps dust, pollen, pet hair, and other airborne particles to help protect your HVAC system and improve indoor air quality. (Included in most systems.)