What is the definition of an outdoor air handler? An outdoor air handler is a type of air handler typically used in heating, ventilation and air conditioning (HVAC) systems. It is designed to condition and circulate air from the outside for use in the building. Outdoor air handlers can be used in both residential and commercial applications. They are typically installed outside of the building, either on the roof or on a platform nearby. The outdoor air handler is responsible for conditioning the air, filtering it, and circulating it into the building. The air handler helps to improve indoor air quality by removing contaminants from the air and introducing fresh air into the building. It also helps to reduce energy costs by allowing the air to be cooled or heated before entering the building. An outdoor air handler is an important component of any HVAC system, providing fresh, conditioned air to the building while helping to improve indoor air quality and reduce energy costs.