Why Is My Furnace Blowing Cold Air?
A furnace that runs but sends cold or lukewarm air has a different symptom than a completely dead furnace.
Try these first
Set the thermostat to HEAT.
Set the fan to AUTO, not ON.
Replace thermostat batteries if needed.
Check the furnace filter for heavy buildup.
Make sure visible registers and returns are not blocked.
Still blowing cold?
If the simple settings and airflow checks do not restore heat, stop there rather than opening burner, gas or electrical components.
Common questions
Why is my furnace blowing cold air when the heat is on?
Common first checks include making sure the thermostat fan is set to Auto instead of On and checking for a dirty filter. If the furnace continues circulating unheated air, it may need professional diagnosis.
Can thermostat settings make a furnace blow cold air?
Yes. With the fan set to On, the blower can circulate air even when the burners are not actively heating. Set the fan to Auto for normal heating cycles.
Can a dirty filter cause cold air or short cycling?
Restricted airflow can contribute to overheating and safety shutdowns, which may leave the blower running without normal heat. Check and replace a visibly dirty filter.