what is a condensing furnace

A condensing furnace is a type of high-efficiency furnace that has a secondary heat exchanger which condenses hot exhaust gases to extract the "waste" heat before it wafts up the chimney. The heat-extraction process with the secondary heat exchanger is so remarkably efficient that the hot exhaust gases are cooled to the point where they can safely exit your home inside a plastic pipe installed through a side wall. The combustion exhaust gases are passed through a secondary heat exchanger that absorbs much of the remaining heat from the gases. As the gases cool, they condense to form water and carbon dioxide, which together form carbonic acid. The water (called condensate) drips out through a drain pipe, and the remaining flue gases are vented to the outdoors through a plastic pipe. Unlike conventional furnaces, a condensing furnace often uses a sealed combustion chamber and direct-vent combustion air. The combustion air intake usually is piped from the exterior of the home to the furnace. This means the furnace does not take air already heated by the furnace and use it for combustion. Condensing furnaces have a second heat exchanger that can extract extra heat from the water vapor that would normally be vented out of your home, allowing them to make more use of the energy that they consume and can significantly reduce their operating costs. Condensing furnaces have AFUE ratings of at least 90 percent, with some models reaching up to 98 percent.