A condensing furnace contains a secondary heat exchanger for what purpose?

A condensing furnace contains a secondary heat exchanger for what purpose?

• A. A secondary heat exchanger that condenses exhaust gases to extract latent heat.
• B. A single-stage burner with no secondary heat exchange.
• C. An external water cooling coil.
• D. A ventless operation requiring no exhaust.

Answer: (A)

Recovering heat from exhaust gases is the main idea here. In a condensing furnace, the combustion products include water vapor. The secondary heat exchanger cools the exhaust enough for that water vapor to condense, and when it condenses, it releases latent heat. That additional heat is transferred to the indoor air, so you get more warmth from the same amount of fuel, which is why these furnaces achieve higher efficiency (AFUE). Because the condensate is acidic, the system must drain it and be built with corrosion-resistant materials; venting is also designed for cooler, condensate-laden exhaust, often using PVC. This setup isn’t about a simple single-stage burner, an external cooling coil, or ventless operation, which is why the secondary exchanger’s role is specifically to condense exhaust and recover latent heat.

Recovering heat from exhaust gases is the main idea here. In a condensing furnace, the combustion products include water vapor. The secondary heat exchanger cools the exhaust enough for that water vapor to condense, and when it condenses, it releases latent heat. That additional heat is transferred to the indoor air, so you get more warmth from the same amount of fuel, which is why these furnaces achieve higher efficiency (AFUE). Because the condensate is acidic, the system must drain it and be built with corrosion-resistant materials; venting is also designed for cooler, condensate-laden exhaust, often using PVC. This setup isn’t about a simple single-stage burner, an external cooling coil, or ventless operation, which is why the secondary exchanger’s role is specifically to condense exhaust and recover latent heat.