The most common reason a furnace fan won't stop is the thermostat's fan setting. If it's set to "On" or a circulation schedule, the fan runs whether or not the furnace is heating. Set the fan to "Auto" and give it a few minutes. If the fan still runs with no call for heat, the cause is inside the furnace, and it needs a professional.
Safety first: If a CO alarm goes off, leave the home now and call 911 from outside. If you smell gas, leave and, from outside, call 911 and Enbridge Gas's emergency line at 1-866-763-5427. On propane, call 911 and your propane supplier.
Is it normal for the furnace fan to keep running after the heat shuts off?
For a short time, yes. Many furnaces keep the fan going briefly after the burners stop. The U.S. Department of Energy's furnace fan energy analysis calls this the "blower off delay," the time between burner shutdown and blower shutdown. What isn't normal is a fan that keeps running long after that, with the thermostat on Auto and no call for heat.
What thermostat settings make the fan run all the time?
The fan setting is the usual culprit. "On" runs the fan continuously. Many programmable and smart thermostats can also run the fan on a schedule, and some have a ventilation mode that runs it for a minimum period each hour if it hasn't run for heating or cooling. Natural Resources Canada's guide to heating with gas describes these continuous, scheduled and ventilation fan modes.
Check these on the thermostat
- Set the fan to Auto, not On or Circulate.
- Look for a fan schedule or a "minimum fan runtime" in the menu or app.
- Check for a ventilation or air-quality mode that runs the fan.
- Wait a few minutes after changing anything, since the fan may finish its delay first.
If the screen is blank or won't respond, our guide for when the thermostat says heat but the furnace won't start covers display and power problems.
Is a fan that runs all the time bad for my furnace?
Running the fan on purpose isn't a fault. Natural Resources Canada says continuous circulation can give more even temperatures, but your electricity use may go up if the furnace doesn't have an efficient fan motor. It also says that when the fan runs, heat loss can rise if leaky ducts pass through an exterior wall, attic or crawl space. A fan running when nobody set it to is different, and worth a call.
Why the air may feel cool
Natural Resources Canada notes that air from a forced-air system can sometimes feel cool even though it's warmer than the room, much like a breeze. With the fan on continuously, it also moves unheated air between heating cycles. If the vents blow cold air during a heating cycle, see our furnace blowing cold air guide.
Could a dirty filter keep the fan running?
It's worth checking. A clogged filter restricts airflow, and Natural Resources Canada warns that restricting the air going back to the furnace can trigger the furnace's high heat limit switch and shut it down during the heating season. Check the filter and replace it if it's dirty. Our dirty furnace filter guide shows how to find and change it safely.
The thermostat is on Auto and the fan still won't stop. What now?
Then the cause is most likely inside the furnace or its controls, such as a control or relay that keeps calling for the fan, or a safety switch that's tripped. None of those are homeowner repairs. Don't open panels, bypass switches or touch wiring. Note what the status light is doing, whether there's any heat, and when it started, then call.
Stop and call if
- The fan runs non-stop with the thermostat on Auto and no call for heat
- The fan runs but the house is getting colder
- You smell burning or hot wiring
- The status light is flashing a code
- The fan stopped and started repeatedly after you changed the filter
One reset at most
If the fan runs and there's no flame, don't keep cycling the power. Our guide for a furnace that won't ignite explains the single reset to try before calling.
Is a furnace fan that won't stop an emergency?
It depends on whether you still have heat. A fan running on a schedule in a warm house can wait for a daytime call. A fan running with no heat on a cold Barrie night, a burning smell, or a home with babies, older adults or someone unwell needs help now. Furnace Repair Barrie answers 24/7 at (249) 209-2216, and our 24/7 emergency furnace repair page lists what to have ready.
Tell us
- Your thermostat's fan setting and any schedules you found
- Whether the house is heating
- The status light pattern, if any
- When you last changed the filter
- Your town and whether you heat with natural gas, propane or oil