A condensing furnace is a furnace with an AFUE of 89% or higher. Efficiency is achieved by extracting heat from the exhaust gases to the point where water is condensed out of the gases.

Traditional Furnace vs. Condensing Furnace

Traditional furnaces are built with just one heat exchanger. During the combustion process that takes place inside of this heat exchanger, a certain amount of the heat that is produced is lost up the chimney in the form of water vapor. What this means is that traditional furnaces lose a significant percentage of the heat that they use energy to produce.

Condensing furnaces have a second heat exchanger that is able to extract extra heat from that water vapor that would normally be vented out of your home. This allows them to make more use of the energy that they consume and can significantly reduce their operating costs.

How A Condensing Furnace Works

At the beginning of the heating process, a condensing furnace works similar to a traditional furnace. Gas burners deliver heat into the first heat exchanger and the combustion process leaves a by-product of hot water vapor. That water vapor is next sent to the second heat exchanger where it is condensed and turned into a liquid.

When a gas turns into a liquid, it releases heat. Your furnace is able to use that extra heat to warm your home. The resulting liquid is then drained out of your home through a PVC pipe.

Special Needs

Condensing furnaces offer higher efficiencies and better comfort, but they also require more care than traditional 80% AFUE furnaces.

With traditional furnaces, you mainly just have to check for cracks in the heat exchanger and do a combustion safety test, but condensing furnaces have condensate drains and secondary heat exchangers, which can become plugged, as well as additional safety devices, pressure switches, and other controls that need to be tuned up and/or adjusted annually.

Lack of regular maintenance can lead to system lockout, decreased efficiency, and premature component failure.