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Why Is My Furnace Blowing Cold Air?


Your furnace gets a long summer vacation from heating duties, but once winter is on its way, it better be blowing warm air! Have you turned on your furnace just to find cold air is blowing out of the vents when the heat is on? As frustrating as this may be, the answer may be a simple fix.

If a furnace blowing cold air has you stumped, here are some situations that might explain what’s going on:

  • It’s normal – If you’re only getting a bit of cold air when your furnace first kicks on, but the air is nice and warm after a few minutes, it’s likely fine. Think of it like turning on a hot water tap. The same effect happens with your furnace. It must push out the cold air from the vents before the warm air can come through.
  • Thermostat – If there’s a constant flow of cool air coming from your vents, you probably have your thermostat set incorrectly. When you turn your furnace on for the first time, be sure that the fan is set to “auto” and not “on.” When your fan is set to “auto,” it will only come on when the furnace is on, instead of running all of the time.
  • Pilot light – If your furnace is only blowing cold air, your pilot light may be out. Double check your pilot light, and if it’s gone out, relight it. If you have to keep relighting your pilot light, contact a heating professional for an expert furnace repair diagnosis.
  • Dirty sensors – If your furnace starts out warm but turns cold quickly, you could be dealing with a dirty flame sensor. A dirty flame sensor tells the furnace to turn off the burner, thus resulting in cold air after it’s initially warm. It’s best to call a heating professional to clean the sensor. Making sure to have annual furnace maintenance performed will help you avoid this issue in the future.

If a furnace blowing cold air is your issue, or if you need help with other home comfort issues, contact the professionals at HVAC & Plumbing Unlimited. We proudly serve homeowners in the Northern Virginia area.

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