A highly efficient furnace is the result of careful engineering based on eliminating the weaknesses of older furnace models. In particular, a highly efficient furnace prevents heat from escaping up your vent pipe and makes the output of your furnace more responsive to the cooling demands inside your home. By learning more about how furnaces work, you can choose the type that is right for you. 

Heat Exchangers

Furnaces produce heat by the combustion of fuel. This heat is contained in the exhaust gases thus created. Thus, a furnace has to have some mechanism in place to extract the heat from the exhaust gases without allowing harmful gases to get into your home. Older furnaces will have a heat exchanger that is designed to leave just enough heat in exhaust gases to allow them to rise out of your home through a vent pipe. A heat exchanger is really nothing more than a series of metal tubes and the fan that pushes air from inside your home over these tubes. The exhaust gases heat the metal tubes, which then heat the air flowing over them. Because of the need to vent exhaust out of your home, older furnaces top out at about 83% efficient. 

Newer furnaces include a second heat exchanger, which allows the furnace to extract so much heat that the water vapor present in the exhaust gases condenses back to a liquid, and the other gases dissolve back into the water. They can then be removed from your home via a drain pipe. 

A Variable-Speed Fan

While extracting as much heat as possible is important, a furnace that runs at full blast to cool a home, then shuts off, runs at full blast, etc., will use more gas than a furnace that runs at full blast to heat your home to the desired setting and then runs at a lower speed to maintain the desired temperature. Thus, you should not just look for just a condensing furnace; you should also look for a modulating furnace, or in other words, a furnace with a variable-speed fan. 

The most efficient furnace models top out at about 98.5% efficiency, which means that for ever dollar you spend on heating your home, you are wasting less than two cents. That's impressive. If you are having a hard time figuring out which furnace models come with which components, it may help to sit down with a furnace technician from a heating company and discuss your options. In any case, the money you spend on buying a highly efficient furnace will help you to save money on operating costs. In most cases, you end up saving more money than you spend on financing.