The definition of an indoor HVAC system is one that is used to control the temperature, humidity, and air quality of a building or home. It is an acronym for Heating, Ventilation, and Air Conditioning, and is the most common type of system used to regulate the indoor environment. HVAC systems are designed to provide comfort and energy efficiency by controlling the temperature, humidity, and air quality of the space. The system is composed of several components, including a furnace, air conditioner, air handler, and thermostat. The furnace is responsible for providing heat to the space, while the air conditioner cools the air. The air handler is responsible for distributing the air throughout the space, while the thermostat regulates the temperature. HVAC systems are designed to be energy efficient, and they can be used to reduce energy costs. They can also be used to improve air quality, reduce allergens, and reduce noise levels.