Airflow in Heating

Technicians who know to check airflow in cooling sometimes neglect to check airflow in heating. But poor airflow can cause heating issues too. If you have a heat pump that is tripping out on high pressure – check for problems that can affect airflow. Dirty air filters, dirty indoor coils, or duct problems can all cause airflow problems. Since the indoor coil is the condenser in the heating cycle, poor indoor airflow will cause high discharge pressures and hot compressors. These can cause tripped high pressure switches or open compressor internal overloads. You would not want to condemn a compressor because the air filter was dirty!

Electric strips may cycle on the their thermal overloads, or the fusible links may open. Anytime you replace a fusible link in a strip, check the airflow and all problems that can cause poor airflow. A stopped up evaporator coil can cause a problem in the heating cycle, even if you do not have a heat pump because it is creating an airflow restriction. Another problem that can be easy to miss is an overly restrictive CLEAN air filer. Most 1" pleated air filters have a very high static pressure drop even when brand new. Homeowners often replace the lightweight filters with these and inadvertently cause airflow problems.

Gas and oil furnaces can cycle on the high limit due to poor airflow. This can be more difficult to catch because most high limits automatically reset. When a furnace cycles on the high limit, the blower keeps running and the burners cycle on and off. Furnaces often cycle on the high limit when they have an airflow restriction. This will shorten the life of the furnace, and is a dangerous situation because you are depending on the safety control to prevent overheating. If the limit would fail to open, the furnace could dangerously overheat. Remember, good airflow in the heating season is really just as important as in the cooling season.