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Why Does My Furnace Blow Cold Air When I Turn On the Heat?

  • December 13, 2013

When your furnace blows cold air, it could be a simple issue or could require professional help. Some of the reasons for a furnace blowing cold are no cause for alarm, while others may require you to contact your HVAC professional, who can fix the issues associated with a malfunctioning or dirty furnace.

  • Blows cold air at start-up: This is a normal phenomenon and shouldn’t last long. When the blower fan turns on, it blows the cold air inside the ducts first before it starts blowing the heated air from the furnace.
  • Fan is set to on: If you let the fan run continually, even when the furnace isn’t running, it’s natural for the air it’s blowing to feel cold. Some people use their air handler in the summer in the on position to circulate the air or in conjunction with a whole-house air filtration system. That same habit will make you feel cooler in the winter, as if the furnace blows cold air. Moving air always feels cooler, and as the heating system continues to run, air dries out. Dry air always feels cooler than moist air, intensifying the feeling of chill.
  • The pilot won’t light: If your furnace is older, it could have a pilot, and if it won’t stay lit, it could be dirty. Your HVAC contractor can clean it. If you’re lighting the system for the first time, and the pilot doesn’t continue to burn, you may need to keep the match or lighter close to the pilot longer to make sure the thermocouple gets hot. The thermocouple is a safety feature, and when it cools off, it shuts the gas supply off.
  • Dirt on flame sensor. Pilot-less ignition furnaces use a flame sensor to keep the furnace burning once it starts. If the flame sensor is dirty, it won’t transfer the heat to the thermocouple, turning the furnace off too soon. An HVAC technician can clean it and restore your furnace’s heating function.

For help whenever your furnace blows cold air anywhere in Monroe County, contact the pros at Comfort Services.