Why Is My Furnace Blowing Cold Air?

After spending a long day out in the cold, there’s no better feeling than returning to a toasty warm home. But what happens when you come home to your furnace not heating, or even worse, your furnace blowing cold air? Follow these steps to learn how to troubleshoot your furnace blowing cold air and learn when to call for a repair.

1. Review your thermostat’s settings

If your thermostat fan setting is set to the “ON” position, this means that the fan will run continuously whether the unit is heating or not.  Therefore it isn’t uncommon to experience cool air coming from your registers between heating cycles. There are many benefits to running a continuous fan, such as energy efficiency, regulated home temperatures, cleaner air, etc. With the “AUTO” setting chosen, your furnace should only run the fan during a heating cycle. If you’ve had your thermostat for a while, be sure to check the battery level as it may be low and therefore needs to be replaced.

2. Check to see if your furnace has warmed up

Oftentimes a furnace will need a few minutes to warm up when it’s first turned on. Because of this, it’s perfectly normal for cool air to blow from the vents while your furnace warms up. If warm air doesn’t begin to fill your space after a few minutes, continue to follow the steps below.

3. Check the furnace air filter

A dirty air filter will prevent the movement of air through the furnace and raise its interior temperature, causing it to overheat. When your furnace becomes overheated, it signals the safety control to turn off the burners. However, your fan will continue to run, resulting in cold air being blown into your home. To prevent this from happening, we suggest replacing your air filter. Upon doing this, the furnace should cool down and restart, bringing normal airflow back into the system and warm air back into your home. 

4. Check the pilot light

If your furnace’s pilot light goes out, the furnace will blow cold air due to fuel combustion not taking place. If you are comfortable doing so you can relight your pilot light, or call a local utility company or HVAC technician to ensure that it is properly lit. If your pilot light continues to go out or doesn’t light at all, you may need routine maintenance from a heating and cooling professional.

5. Check your furnace’s control panel

When a furnace blows cold air, there may be an issue with the unit’s electronic control panel. If there’s an LED light visible from the front panel of your heating unit, it’s a good idea to record the sequence and number of flashes before resetting the power.  Video of the LED light flash sequence can help a technician diagnose the issue if the reset doesn’t resolve the issue. Another option is to make notes on paper regarding the flash sequence.  Sometimes, the problem can be solved by doing a system reset. First, turn off the power to the furnace at its ON/OFF switch, then wait a few minutes and flip the switch back to ON.  When restarting the unit, pay attention and document any odd sounds or smells coming from the unit as it attempts to reignite.  If this doesn’t correct the problem, we recommend calling one of our furnace repair technicians. 

6. Check for leaking ducts

Sometimes, a furnace blows cold air due to damaged or leaking ducts. Leaks in ductwork allow heat energy to escape, so once heated air reaches your living areas, it no longer feels warm. To fix this, you will need to have your duct leaks pinpointed and repaired by a professional.

If you have completed this checklist and are still having problems with cold air blowing from your furnace, we suggest having your furnace looked at by a Diamond Heating & AirTemp Alaska HVAC  technician, as there may be something more serious happening within your system. Schedule an appointment today and receive $25 off your repair!