Roof Top Units (RTUs) are a type of Heating, Ventilation and Air Conditioning (HVAC) system that are designed to provide efficient heating, cooling, and ventilation to a particular building or space. These systems usually consist of two separate parts – a rooftop condenser and an evaporator – which work together to cool or heat the desired space. With the ability to precisely control temperature, humidity levels and air quality, RTUs have become one of the most popular choices for commercial buildings. So, if you’re wondering exactly what the official business definition of Roof Top Units is, here it is: Rooftop Unit (RTU) systems are centralized air conditioning/heating units located on the rooftop of a building. They provide greater flexibility and improved efficiency in climate control and indoor air quality.