In the new high efficiency furnaces, flue gases leave the furnace at approximately what temperature range?

In the new high efficiency furnaces, flue gases leave the furnace at approximately what temperature range?

• A. 70–90 degrees F
• B. 200–250 degrees F
• C. 115 to 118 degrees F
• D. 135–140 degrees F

Answer: (C)

High-efficiency condensing furnaces recover most of the heat from the combustion gases, so the flue gases exit the furnace much cooler than in older units. Because more heat is extracted, the exhaust leaving the furnace is typically around 115 to 118 degrees Fahrenheit. This cooler vent temperature is a hallmark of condensing operation and aligns with the design that uses highly efficient heat exchange to maximize output. The other ranges don’t fit what’s observed in modern high‑efficiency furnaces: 70–90°F would be unrealistically cold for combustion exhaust, 200–250°F is too hot for a condensing system, and 135–140°F is higher than the typical exit temperature but not as representative as the ~115–118°F range.

High-efficiency condensing furnaces recover most of the heat from the combustion gases, so the flue gases exit the furnace much cooler than in older units. Because more heat is extracted, the exhaust leaving the furnace is typically around 115 to 118 degrees Fahrenheit. This cooler vent temperature is a hallmark of condensing operation and aligns with the design that uses highly efficient heat exchange to maximize output.

The other ranges don’t fit what’s observed in modern high‑efficiency furnaces: 70–90°F would be unrealistically cold for combustion exhaust, 200–250°F is too hot for a condensing system, and 135–140°F is higher than the typical exit temperature but not as representative as the ~115–118°F range.