These furnaces are typically installed in an attic, crawl space, or closet, most often replacing a similarly configured oil furnace. The Horizontal/Downflow Oil furnaces can be installed horizontally or vertically in a downflow (or counterflow) configuration. Return air enters the unit at one end and the supply air leaves at the other. (When installed vertically, return air enters the unit at the top and supply air exits at the bottom.)
Please read this Important Safety Notice.