Why Is My Furnace Blowing Cool Air?

When the temperature outside is hovering in the 30s or below, the last thing question you want to have to ask is “Why is my furnace blowing cool air?” The answer to that question could be several things, so checking these areas could help you solve the problem and get warm air pumping back into your home.


The Thermostat: If you walk by a vent and it is blowing cold air, it could be as simple as you have your thermostat set to “on” rather than “auto”.  When it is set to on, the fan will continuously blow even when the furnace is not heating the air and this causes the air to seem cool.  Set it to auto and if it is still blowing out cool air when the furnace is running, it is likely there is something wrong.

The Filter: Whenever you are troubleshooting your furnace, always check and change the filters. An old filter can block the flow of air and decrease the heating ability of your furnace fan as it blows through a dirty filter. In some models, a clogged filter can cause your furnace burner to shut down so it doesn’t overheat, causing a still-running fan to blow cool air.

The Ductwork: Damaged ductwork causes cold air to get into your duct system. Broken or peeling duct tape, broken mastic, or unscrewed ductwork may break or become damaged at the seams, causing them to leak and become inefficient. Even if your furnace is blowing hot air into the ductwork, by the time it reaches the registers, it may only be blowing cool air. These problems should be checked and fixed by a professional to have your heating system working properly.


If your furnace is still blowing cool air after your troubleshooting, it’s time to call in the professionals. A.B. May Company is your provider for HVAC services in Kansas City and the surrounding areas. Homeowners have trusted us with their heating systems since 1959. Call us at 913-370-4898 today for help with your furnace.