How Long Should the Fan Run After the Furnace Shuts Off?

Do you hear the quiet hum of your HVAC fan even after your furnace's heating cycle is over? This issue impacts countless homeowners who find themselves asking, "How long should the fan run after the furnace shuts off?" 

The team at Inland Empire Comfort is here to explain common reasons why the furnace fan continues to run. We specialize in furnace repair in Riverside and can address this and other concerns you have about your heating system. 

Understanding the Average Furnace Heating Cycle

When you turn your heat on, the furnace will work in cycles until your home reaches the temperature you program on your thermostat. The furnace fan often turns on within a minute of the system beginning its heat cycle. It will stay on for the duration of the heat cycle and then shut off within a few minutes. 

If you notice the fan runs long after the furnace stops producing heat, you'll have to investigate further. The problem may have an easy fix, like adjusting the thermostat, or it could require a professional inspection of your furnace. 

Reasons Why Furnace Fans Stay On 

You now have the answer to the question, "How long should the fun run after the furnace shuts off?" but are probably still wondering what causes a fan to constantly run. You might encounter this issue for the following reasons. 

Thermostat Settings

Whenever you operate your central heating or air conditioning system, make sure that the thermostat is set to "auto" instead of "on." Having the fan set to "auto" means that it will automatically turn on and off with the furnace's heating cycle. When this setting is set to "on," the fan will run nonstop even if the furnace is off. 

Fan Limit Switch Settings

One of the most important safety features in modern furnaces is the fan limit switch. The switch will trigger and turn the furnace off to prevent it from overheating. Like your thermostat, the limit switch setting should be set to "auto" instead of "manual override."

You can easily adjust the settings by looking for a small knob beneath the furnace hood. If the knob is pushed in toward the furnace, the fan limit switch is in manual override mode. Pulling the knob out will get it back into automatic mode so the fan doesn't run constantly. 

Equipment Malfunction

If your thermostat and fan limit switch settings are correct, you could have faulty equipment. The trigger on the fan limit switch may not work properly, or you could have a thermostat wire that short circuits. Have a professional technician inspect the furnace to pinpoint the underlying cause. 

Contact Our Furnace Repair Experts for Service

How long should the fan run after the furnace shuts off? What can you do if the furnace pressure switch goes bad? At Inland Empire Comfort, our technicians can answer these questions and more. 

Reach out to us if you're experiencing issues with your furnace, and we'll perform accurate, affordable repairs. Call (951) 336-1718 to request immediate service.