If the temperature rise of a gas furnace's heat exchanger exceeds the manufacturer's specifications, what should the installer do?

If the temperature rise of a gas furnace's heat exchanger exceeds the manufacturer's specifications, increasing the CFM (cubic feet per minute) is the appropriate action to take. This adjustment increases the airflow through the heat exchanger, which can help reduce the temperature rise by allowing more air to absorb the heat produced.

When the airflow is insufficient, the heat exchanger can become too hot, which may lead to equipment damage and decreased efficiency. By increasing the airflow, the system can maintain a safer and more efficient operation, aligning with the manufacturer's guidelines for temperature rise.

In contrast, adjusting the gas supply or adding insulation does not directly address airflow issues and may result in other problems. Changing the filter may improve airflow only if it is dirty, but it does not directly tackle situations where the CFM is already too low. Thus, increasing the CFM effectively addresses the concern of an excessively high temperature rise in the heat exchanger.