Air Flow Configuration
The direction in which a furnace outputs heat. A furnace may have an upflow, downflow or horizontal configuration. (Horizontal configuration is sometimes called cross-flow configuration.)
- A downflow furnace takes cool air from the top and discharges warm air from the bottom.
- An upflow furnace takes cool air in from the bottom and discharges warm air from the top.
- A horizontal furnace lies on its side, pulling cool air from one side and pushing warm air out of the other.
Upflow furnaces are generally placed in the basement. Downflow furnaces are generally placed in an attic. Horizontal furnaces are used in locations where there is limited space.