The Difference Between Upflow & Downflow for a Residential Furnace

Upflow

• Upflow refers to furnaces that pass air up above the unit as it is heated. Furnaces that use upflow come with air ducts that are installed in attics, upper crawlspaces and walls. Air is then moved horizontally, circulated through this upper system of ducts with the help of air blowers at the bottom of the furnace that push air continually upward. Because these fans fight against gravity, they may require more power usage than other furnace options.

Downflow

• Downflow refers to furnace systems that have air intakes at the top of the furnace, taking in air from higher regions, often through the ceiling, and warming it before passing the air out through the bottom of the unit. In this case, ductwork runs primarily through basement areas and lower crawlspaces where air is circulated. While this allows some of the heat to fall below the house and could be less efficient, it does not require as much fan work to propel the air.

Consideration

• Upflow and downflow systems are both viable options for homeowners. The choice typically depends on the house itself. Houses that have basement regions may be more suited to downflow furnaces, while those that only have attic spaces can use upflow vents instead. The furnace system should fit the house in order to work properly.

Crossflow

• There are also crossflow furnaces, or horizontal flow units, that either take air from the right side of the furnace and pass it through the left, or take it from the left and pass it to the right. Though this type of furnace is more uncommon, it could work well when there is little room for other options and the furnace needs to pump air directly into a wall.