Heating – Systems/equipment or devices which raise the temperature inside rooms.
Ventilation – The air circulation process between outdoor and indoor air. This process can work without any devices (gravitational ventilation) or with some extra devices electricity-powered (mechanical ventilation).
Air Conditioning – Air conditioning is a process to create and maintain certain temperature, relative humidity and air purity conditions in indoor spaces.
HVAC is an acronym for heating, ventilation and air conditioning systems. These systems maintain the optimal temperature in residential and commercial buildings. They ensure that the temperature inside buildings is just right.