Today’s consumer finds a wide array of choices in warm air furnaces based on the efficiency sought, the type of chimney available, and the fan package features.
Efficiency refers to the percentage of fuel purchased that ends up as heat inside your home and the remainder that is exhausted to the outside. Gas furnaces to be installed into a chimney cannot have an efficiency rating greater than 80%.
The first consideration, then, is the chimney. If a sound, properly sized chimney is available (metal b-vent is always reliable) then an 80% efficiency furnace is a cost-effective choice. If the chimney requires lining, a 92% furnace is the best choice. Chimneys require a certain amount of heat to properly perform, and the 92% (condensing) furnaces lose so little heat they are vented directly to the outside, like a dryer, with plastic pipe.
Oil burns much hotter than gas, and so is much more “chimney-friendly.” Efficiencies up to 84% are available in a number of different high quality units.
A popular feature now is a variable speed fan package, or an EMC motor. Both will lower your electric bill and the variable models can improve comfort as well.
Also popular are 2-stage and 3-stage furnaces, which deliver lower BTU outputs on days when full output is not required, providing a longer cycle of warm air flowing out of the vents.
Your salesman will assess the conditions in the home, as well as your interests and potential payback, to provide the best set of options.