Propane furnaces can be very efficient and just as efficient as any other furnace. The efficiency rating of a propane furnace depends on how much of the propane's energy is converted into heat.
Furnaces that are low-efficiency usually have a rating of 80 percent, while a high-efficiency furnace has an efficiency rating between 90 and 95 percent. There are also very high-efficiency furnaces that have ratings of over 95 percent.
Homeowners who upgrade to a high-efficiency furnace generally notice a dramatic decrease in fuel costs. However, people who live in a climate without cold winters may not see a difference between a high-efficiency or very-high-efficiency unit.