What to Do If You Find Your Furnace Blowing Out Cold Air

A furnace blowing out cold air is about as useful as an air conditioner producing hot air. Reliable heating for your home is a fundamental furnace function. When the furnace doesn’t deliver, you’ll probably want qualified service ASAP. Here are a couple of simple reasons for a furnace blowing out cold air, plus two more that will require professional attention.

  • Wrong thermostat mode. Check the HVAC thermostat mode to verify that it’s set to “Heat” and not “Cool.” While this may seem like a no-brainer, it does happen occasionally, and it’s definitely one reason why you might be feeling colder at home instead of warmer.
  • Incorrect thermostat fan setting. If the system fan is set to “On” instead of “Auto,” the fan will circulate air nonstop, including between heating cycles, when the furnace doesn’t produce warm air. During those intervals, cold air may be noticeable coming out of the vents. For heating, the correct thermostat fan setting is “Auto.” This means the system fan stops circulating air during the intervals when the furnace isn’t generating heat.
  • Airflow blockage. If system airflow is obstructed somewhere in the ductwork, a safety sensor may automatically shut off the furnace burner. After the heating function is off, the system circulates unheated air to cool down furnace components. Turn off the system, as professional HVAC service is required to identify and resolve the airflow issue. Then, reset the safety sensor and restart the furnace.
  • Defective pilot light or electronic igniter. If the furnace burner fails to ignite when the thermostat signals, cold air will circulate instead of heat, resulting in the furnace blowing out cold air. The pilot or igniter are critical to safe heating and require a certified technician to diagnose and repair or replace. Shut down the furnace at the thermostat and call your HVAC contractor.

For professional service, including 24/7 emergency response to resolve a furnace blowing out cold air, contact NisAir Air Conditioning and Heating.

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