Why is My Furnace Blowing Cold Air?

August 04, 2016

A furnace blowing cold air would making any homeowner hot in the face. It’s annoying, right? 

Troubleshooting this issue depend on how exactly the furnace is blowing cold air: 

  • Does your furnace blow warm air sometimes and cold air other times? Read the first section of this article.
  • Does your furnace always blow cold air? Read the second section.

Furnace blows warm air for awhile, then blows cold air

furnace that blows warm air sometimes but cold air other times is usually caused by one of 2 things: either you have your thermostat fan set to ON or your furnace is overheating.

Problem: Thermostat set to ON
The fan in your furnace blows the heated air through the vents in your home. If set to ON, the fan will continue to blow air, even when the furnace isn’t actually heating.

This can make it seem like the furnace is blowing cold air, though it’s really just blowing room-temperature air.

Try this: Next time you feel cold air, check the thermostat to see if your home’s temperature has reached your set temperature. If it has, simply change your fan setting to AUTO and your fan will only blow when the furnace is actually heating. (This setting is also more energy efficient.)

If you notice that the thermostat is not reaching your desired temperature, it’s most likely that…

Problem: Furnace is overheating
If your furnace overheats, a safety switch will shut the burners off, allowing the fan to continue blowing air to cool down the heat exchanger. Once cooled off, the furnace will restart and heat for awhile before overheating and continuing the cycle.

Try this: Change your air filter. A dirty air filter is one of the most common causes of an overheated furnace. A dirty filter restricts the airflow coming into the furnace, suffocating it and making it work extra hard. This causes the furnace to overheat.

If your thermostat is set to AUTO and you changed your air filter and are still having issues, you should contact a professional heating repair company in Kansas City.

Furnace always blows cold air

This problem is a bit more difficult to troubleshoot, but here are the most common problems. Problem: Thermostat not set to HEAT Hey, it happens. Just double-check and make sure your thermostat is set to HEAT and the fan is set to AUTO. Problem: Burner not lighting If you have a gas furnace, it could be blowing cold air because the burner isn’t igniting when it should be. The most likely reasons for this are: Igniter malfunction — Your igniter can simply go bad and not light. Pilot light is out — If you have an older furnace, you may have a standing pilot light that has blown out and needs to be re-lit. (Related: Why does my pilot light keep going out?) Gas supply problems — Either the gas company is having problems or the supply to your furnace needs to be adjusted. Condensate line clog — New, high-efficiency furnaces have condensate drains. If they become clogged, the water can back up and activate a switch that keeps your burners from lighting. Problem: Major duct leaks Holes and leaks in air ducts suck in cold air from your attic and crawlspace and blow it into your home through your ducts. Learn more about leaky air ducts.

Get a professional diagnosis from a KC area HVAC contractor

As you can see, many different problems can cause your furnace to blow cold air. For an accurate diagnosis, you need a professional heating repair company to take a look.

If you live in the Kansas City area, contact Santa Fe Heating. We serve Overland ParkOlatheLeawoodLenexaShawnee, Gardner, and more with expert heating and air conditioning service.