I see the terms "upflow", downflow", and "horizontal" used when describing furnaces and air handlers. What does this mean? Back
These three terms refer to the furnace air delivery configuration.
Upflow means that the supply (warm) air is delivered upward, off the top of the furnace into an overhead duct system.
Downflow means the supply air is delivered from the bottom of the furnace into a duct system beneath it.
Horizontal means the furnace will lay on its side for use in an attic or tight basement.
