How many heat exchangers does a condensing furnace have?

A condensing furnace is designed to achieve greater efficiency by utilizing two heat exchangers. The first heat exchanger is responsible for extracting heat from the combustion gases to heat the air that is circulated through the home. This is similar to a traditional furnace.

The second heat exchanger in a condensing furnace further extracts heat from the exhaust gases after the first heat exchanger has cooled them. This is accomplished by condensing the water vapor in the exhaust gases, which releases additional thermal energy. As a result, the water produced during this process is drained away via a condensate drain.

Utilizing two heat exchangers allows condensing furnaces to achieve efficiencies significantly higher than conventional models, often reaching annual fuel utilization efficiency (AFUE) ratings above 90%. This two-stage process is what leads to the name "condensing" furnace, as it actively condenses the combustion byproducts to maximize heat recovery.

The other options reflect either misunderstandings about the operational design of a condensing furnace or incorrectly outline its components. In summary, a condensing furnace's dual heat-exchanger system is key to its enhanced efficiency and performance.