HVAC stands for Heating, Ventilation, and Air Conditioning. It is a collective term for all the different types of cooling and heating systems used to change the temperature and humidity indoors. HVAC systems also improve indoor air quality through mechanical ventilation and filtration. The goal of an HVAC system is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer.

An HVAC system has multiple units and parts, both inside and outside your home, that all work together doing different jobs to bring you the complete home comfort you need. The components of an HVAC system include a heating unit, a cooling unit, ducts to move the air, and a thermostat to regulate the systems function. The means of air delivery and removal from spaces is known as room air.

HVAC systems can be used in both domestic and commercial environments. They are an important part of residential structures such as single-family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships, and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

In summary, an HVAC system is a system that controls the temperature, humidity, and purity of the air in an enclosed space, with the goal of providing thermal comfort and acceptable indoor air quality.