What can cause a high Delta T in a furnace?

When analyzing high Delta T in a furnace system, low airflow is a primary factor that can lead to an increased temperature differential between the air entering the furnace and the air leaving it. The Delta T, or temperature difference, reflects how effectively a furnace is heating the air.

If the airflow through the furnace is restricted, less air is being heated at any given time. This means that the air picking up heat from the heat exchanger will be at a much lower volume, resulting in a higher temperature difference from the intake to the output. Essentially, the furnace may operate longer to reach the desired temperature, and because less air moves through the system, the output air temperature becomes comparatively higher than that of the input.

Understanding the relationship between airflow and heat transfer is crucial in diagnosing and resolving issues related to high Delta T in furnace operation. Factors such as high humidity, a faulty thermostat, and a dirty air filter can contribute to efficiency issues but do not directly affect the airflow in the same manner as low airflow does when it comes to creating a greater Delta T.