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

Understanding your HVAC system can be a bit tricky, especially when it comes to the operation of the furnace and its fan.

One common question homeowners ask is, “How long should the fan run after the furnace shuts off?”

In this article, we delve into this and related topics to give you a clearer understanding of your furnace operation.

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

Typically, the furnace fan should run for about 3 to 5 minutes after the furnace has shut off.

This is designed to take advantage of the residual heat within the furnace at the end of the heating cycle, effectively increasing the energy efficiency of your system.

5 Reasons Why Your Furnace Fan Doesn’t Shut Off

1. Faulty Thermostat

If your furnace fan doesn’t shut off, your thermostat may be set to continuous fan operation. To fix this, simply switch the fan setting on your thermostat from ‘ON’ to ‘AUTO’.

2. Faulty Fan Limit Switch

The fan limit switch controls the furnace blower. If it’s faulty, the fan may run continuously. Contact an HVAC professional to inspect and potentially replace the fan limit switch.

3. Wiring Issues

Wiring problems can cause the furnace fan to run non-stop. If this is the case, it’s best to call an HVAC technician as dealing with electrical issues can be hazardous without proper training.

4. Relay Stuck in the “Closed” Position

If the relay is stuck in the “closed” position, the fan will continue to run. A professional will need to replace the relay.

5. High Limit Switch Failure

The high limit switch turns off the furnace if it gets too hot. If it fails, the furnace fan may keep running to cool down the furnace. If the limit switch is faulty, a professional should replace it.

Why is My Blower Motor Turning Off and On When Furnace Isn’t Heating?

Your blower motor might be turning on and off due to a malfunctioning control board, a worn-out motor, or a problem with the thermostat. Each of these problems requires a different fix:

  • A malfunctioning control board will likely need to be replaced by a professional.
  • A worn-out motor may require lubrication or replacement, depending on its condition.
  • Thermostat issues can be resolved by either replacing the batteries, resetting the thermostat, or getting a new one.

How Long Should Furnace Fan Run Per Hour?

The length of time a furnace fan should run per hour depends on your specific heating needs and the outdoor temperature.

On colder days, the furnace fan might run almost continuously to maintain the desired indoor temperature. In milder weather, it could run for only a few minutes per hour.

Should a Furnace Fan Run All the Time?

Running the furnace fan continuously can help circulate air evenly throughout your home, improving comfort and air quality. However, this will increase your energy usage. Consult with an HVAC professional to discuss whether continuous operation is suitable for your situation.

Why is Furnace Fan Running When Thermostat is Off?

If your furnace fan runs when the thermostat is off, there could be an issue with your thermostat, a wiring problem, or a malfunctioning control board. Each of these situations requires the attention of an HVAC professional for diagnosis and repair.

How Long Should Furnace Burners Stay On?

The burners on your furnace should stay on until your home reaches the temperature set on your thermostat, after which they will shut off.

However, if the burners are turning off before your home is adequately heated, you may be dealing with a malfunctioning thermostat or a dirty furnace filter that needs replacing.


Understanding the intricacies of your furnace and its fan operation is key to maintaining a comfortable and energy-efficient home.

Remember, always consult with a professional HVAC technician if you’re unsure about any aspect of your HVAC system’s operation.

Proper furnace maintenance not only ensures the longevity of your system but also enhances the overall comfort of your home.

About Roy Cohen

Roy Cohen has a burning passion for heating, cooling, and ventilation. He aims to help you save money on expensive repairs and bring you the best HVAC products. He has years of experience behind him in HVAC repair and garage maintenance.

You can find Roy at his LinkedIn or his email: [email protected]

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