In new high efficiency furnaces, flue gases leave the furnace at ____________ to ____________ degrees F.

In new high-efficiency furnaces, flue gases leave the furnace at a temperature range of 115 to 118 degrees Fahrenheit. This lower range of exhaust gas temperature is a key characteristic of high-efficiency systems.

High-efficiency furnaces are designed to extract as much heat as possible from the combustion process before the flue gases are expelled. By producing cooler flue gases, these furnaces maximize heat transfer to the air within the home, which is a critical aspect of their efficiency. The reduced temperature also minimizes heat loss in the exhaust, allowing the system to operate more effectively and reducing fuel costs over time.

The specific exit temperature range is important for several reasons, including preventing condensation of moisture in the flue, which can lead to corrosion of the venting system, and ensuring optimal efficiency by maintaining the furnace's ability to recover exhaust heat. This operational characteristic is what distinguishes high-efficiency furnaces from older, less efficient models, where flue gas temperatures were significantly higher.