What Causes a Furnace to Blow Cold Air?
If your furnace is blowing cold air, it will not properly heat your home.
This type of issue is actually a very common HVAC problem to have.
There are several possible causes of a furnace blowing cold air, so it can be hard to give advice without gathering further information.
However, below are some common causes that will cause your heating system to blow cold air.
Thermostat is Set to ON Position
Is your thermostat set to the ON position instead of the AUTO position? Check your thermostat for this important setting.
If you have your thermostat set to ON instead of set to AUTO, the furnace blower will blow air continuously even when the burners aren’t warming the air, causing cool air to come out of your registers.
By setting your thermostat to AUTO, the blower will only blow air when the furnace is heating. Some people choose to leave their thermostat on the ON position as it helps filter air throughout the house.
Your Furnace Has Overheated
It is possible that your furnace has overheated.
Your furnace has a safety mechanism inside called a “limit switch” that monitors temperature and will shut down when it becomes too hot to prevent a fire from starting inside your furnace. The most common cause of a furnace overheating is a dirty air filter.
Your furnace filter protects your furnace.
If your filter is dirty, not much air can pass through and in turn, your furnace will start to overheat.
Don’t ignore this problem. Repeatedly overheating your furnace will damage your furnace’s heat exchanger which is a very costly furnace repair!
Furnace Pilot Light is Out
Older gas furnaces have standing pilot lights instead of an electronic ignition.
If you have a furnace that was installed in 1996 or prior, it’s likely you have a pilot light in your furnace and it may be out, causing your furnace not to ignite.
If your pilot light is out, re-light it. If it refuses to light, be sure the gas supply is on to your furnace and the gas valve on your furnace is set to the on position.
Also check to make sure the pilot light is not dirty as that can cause it not to light as well.
If your pilot light still will not stay lit, you may have a problem with your thermocouple and it needs to be adjusted or replaced.
If you don’t feel comfortable doing this, contact us and we can help!
Empty Oil or Propane Tank
If you live in a rural area and utilize an oil or propane furnace, it’s a good idea to ensure that your oil or propane tank is not empty.
If this is the case, the blower motor on your furnace would continue to run and circulate the cool, room temperature air.
Bad Flame Sensor
Your furnace will not stay lit if the flame sensor goes bad. This is a very common furnace repair.
This device works with the gas valve to let it know that there is actually a flame present so the gas valve doesn’t just leak gas into the furnace without a flame being present.