What Do Upflow, Downflow, and Horizontal Mean?

What these three terms mean

When you shop for a furnace or air handler, you will see the words upflow, downflow, and horizontal. They all refer to the same thing, the direction the equipment delivers supply air into your duct system. The right choice depends on where the unit sits in your home and how the ductwork is routed.

Upflow, downflow, and horizontal explained

An upflow unit is common in basements and closets where ducts run overhead. A downflow unit suits homes where the ductwork runs under the floor or through a crawl space, such as a unit installed in a closet on a main floor. A horizontal unit fits low clearance spaces like attics and crawl spaces, where there is no room for a tall vertical cabinet.

Why the configuration matters

Matching the airflow direction to your existing ductwork is important. A furnace or air handler has to be ordered in the configuration that fits your installation. Some furnaces are multipoise and can be set up for more than one orientation, while others are dedicated to a single direction. Always confirm the configuration before you order so the unit lines up with your supply ducts and return.

If you are not sure which orientation your home needs, look at where the air handler or furnace sits and which way the main supply duct runs. AC Direct offers free technical support to help you confirm the right configuration before you buy.