Both heating and air conditioning work on the principle that heat always moves from a warm object to a cooler one, just as water flows from a higher to a lower level. Furnaces and heaters put heat into the air to make your home warmer; air conditioners remove heat to make your home cooler.

Heating or cooling through conduction typically takes place at the building envelope (the outside walls, windows and doors) where warm or cold air outside causes the molecules of the envelope to increase vibration or decrease vibration which in turn causes a heat loss or gain inside of the building.

Air Conditioning It works by removing heat and humidity from inside the building and releasing it outside, using a system of coils filled with a refrigerant. Modern HVAC systems are designed for efficiency and can include air filters, humidifiers and dehumidifiers to further refine the indoor environment.

Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning.