Downflow describes the direction in which supply and return air move through a rooftop HVAC unit.

In a downflow configuration, conditioned supply air leaves through the bottom of the rooftop unit and enters the building through roof openings, a rooftop curb and connected ductwork.

Where is downflow commonly used?

Downflow is widely used when the rooftop unit is installed directly above the conditioned space and the main supply and return ducts are located below the roof.

What is a rooftop curb?

A rooftop curb provides a structural and weather-resistant interface between the RTU and the roof. It can also provide openings for supply air and return air to connect directly into the building ductwork.

Is downflow the only rooftop configuration?

No. Depending on the product, rooftop packaged units may support downflow, horizontal discharge or convertible airflow arrangements.