Condensing Furnace
A high-efficiency gas furnace (90%+ AFUE) that captures extra heat by condensing water vapor out of its exhaust. It vents through PVC pipe instead of a metal flue and needs a condensate drain — two install details that affect replacement cost.
The longer answer
Condensing furnaces extract latent heat from water vapor in combustion exhaust — heat that older 80% AFUE units vent straight outdoors. The trade-off: acidic condensate that must drain (often to a floor drain or pump) and PVC venting instead of metal flue pipe, which sometimes requires re-routing the vent path at replacement.
The AFUE jump from 80% to 95% is real fuel savings across Seattle's long heating season, but the install premium (vent rework, condensate plumbing) belongs in the comparison. On homes with sound existing PVC venting from a prior condensing unit, like-for-like replacement is the cheapest upgrade path.
The Seattle angle
Most furnace replacements in the Seattle area are now condensing units — WA energy code and the economics of 90%+ AFUE make 80% non-condensing swaps increasingly rare except on tight-budget projects.
Guides that use this term
Where this decision happens
Nearby in the glossary
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