A temperature rise check measures the difference between return air and supply air during heating operation, verifying proper heat exchanger function and gas furnace combustion efficiency. Proper temperature rise typically ranges from 40-60 degrees Fahrenheit for standard efficiency furnaces and 30-50 degrees for high-efficiency systems. Readings outside design specifications indicate airflow restrictions, heat exchanger fouling, or combustion problems.
Technical Details
Technicians measure return air temperature and supply air temperature using digital thermometers or thermocouple probes, then calculate the difference. Design temperature rise varies by furnace capacity and airflow rate. For example, a 60,000 BTU furnace with 1000 CFM airflow might target 60°F rise. Excessive temperature rise above 80°F indicates restricted airflow or weak ignition; insufficient rise below 30°F suggests excessive airflow or heat exchanger leakage. Measurements should occur after system stabilization at steady-state operation.
Practical Significance
Temperature rise verification ensures furnace safety and efficiency during heating season. Abnormal readings prevent potential overheating, carbon monoxide issues, or heat exchanger damage. Annual temperature rise checks before heating season maintain system reliability and protect occupant safety.