Comfort-Aire manufactures four gas furnaces for residential use and one oil furnace series for commercial use, as of March 2015. Gas furnaces range from 80 percent efficiency to 95 percent efficiency, while the oil furnace series contains capacities from 225,000 to 450,000 British thermal units per hour.
The least-efficient model is 34.5 inches tall, and the unit replaces older furnaces or serves as a new installation. The most-efficient unit fits into most spaces vacated by older furnaces. Furnaces come pre-assembled, pre-wired and ready to install. Heat exchangers come with limited, lifetime warranties for residential furnaces. Oil furnaces for commercial buildings can be installed horizontally or vertically, and Comfort-Aire touts these larger furnaces for churches, schools and other buildings.