A furnace nameplate specifies a temperature rise of 40F-70F. Temperature measurements indicate a rise of 80F. The most appropriate action is to:

When the temperature rise measured is significantly higher than the specified range indicated on the furnace nameplate, it suggests that the system is not operating efficiently. A temperature rise of 80°F, exceeding the recommended maximum of 70°F, can indicate an issue with airflow or heat exchange within the furnace.

Increasing the fan speed is an appropriate action in this scenario because it can help to improve airflow through the furnace. By increasing the fan speed, the system is better able to circulate air, which can facilitate more effective heat exchange with the furnace, leading to a decrease in the temperature rise. This adjustment works to ensure that the air passing through the heat exchanger is adequately cooled, bringing the temperature rise back into the safe and efficient operating range specified by the manufacturer.

Adopting this approach helps in mitigating overheating issues, ensuring better performance and longevity of the furnace, and ultimately enhancing comfort and safety within the living space.