An indoor air handler is a device used to regulate the air quality inside a building. It is responsible for controlling the temperature, humidity, and air flow of the indoor environment. The air handler is usually located in the attic, basement, or other enclosed space, and is connected to the heating and cooling system. It is also responsible for filtering and purifying the air, as well as controlling the ventilation. The air handler is designed to provide a comfortable and healthy environment for the occupants of the building. It is important to keep the air handler clean and maintained to ensure it is working properly and efficiently. Regular maintenance and cleaning of the air handler can help reduce energy costs and improve air quality.