An HVAC system includes equipment for generating heat that is used to warm the interior of a space. This equipment may be a furnace, a boiler, or a heat pump. It may heat only one room, one area, or an entire building. Heat sources include electricity, propane, heating oil, or natural gas. 

An HVAC system includes equipment for generating cool air that is used to bring down the temperature for the interior of a space. This equipment is typically referred to as an air conditioner. Equipment may be inside or outside. It may also filter air and control humidity.

A ventilation system is essential to an effective HVAC system. It is separate from heating or air conditioning, but works together with both to maintain airflow. This airflow is used to effectively heat or cool the internal space. It works in conjunction with air conditioning to filter air and control humidity.