If a furnace nameplate specifies a temperature rise of 40 to 70 degrees but measurements indicate a rise of 80 degrees, what should be done?

When a furnace nameplate specifies a temperature rise of 40 to 70 degrees but measurements indicate a rise of 80 degrees, it's important to recognize that an excessive temperature rise could indicate airflow issues. Increasing the fan speed can help to improve airflow through the furnace, which can bring the temperature rise more in line with the specified range.

By increasing the fan speed, the system can circulate air more efficiently, thereby reducing the overall temperature rise. This adjustment can also help ensure that the furnace operates more safely and effectively, preventing potential overheating or damage to the system.

Adjustments to gas input, thermostat settings, or replacing the filter may not directly address the issue of high temperature rise due to airflow limitations, making increasing the fan speed the most appropriate action to take in this scenario.