Why is My Furnace Blowing Cold Air?

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furnace blowing cold air

Why is My Furnace Blowing Cold Air?


December through February tend to be our colder months around here in Jackson, TN. Once you leave your house between traveling, working in cold spaces, heat at work not being sufficient, most of us freeze throughout the day. When you get home for the day, you expect to walk in and the house be warm. The last thing you want to find is your furnace blowing cold air!

Most people are not even sure what a furnace is besides the generic “the thing that heats your house.” So, here is a basic understanding of just how your gas furnace works:

The first thing you do is set your thermostat to your desired temperature for your home or business. This action sends a signal to your furnace.
After this, your gas furnace control board will do a check to make sure that all of your system’s safeties are operational. (The furnace’s safeties are monitored constantly throughout the heating process and if any of them are tripped, the furnace will enter into a shut-down process).

Then, the gas ignites in the furnace which produces the heat that heats your desired area. This heated air is sent out through vents to the desired area via the duct work.

Once your furnace has heated your desired area to the temperature you have selected, it will stop running. Whenever the temperature of your desired area falls below the temperature you have set on the thermostat, the furnace will kick back on and heat the area again until the desired temperature is reached.

This process described is one of many different variations according to the system setup. There are different variations of furnaces and thermostats nowadays in these modernized times, but this process described is the basic idea of it.

So why is your furnace blowing cold air?

furnace blowing cold air

Here are 3 possibilities:

1) Your Thermostat fan is set to “ON”

If the blower of the furnace is constantly running or if cold air is only blowing out some of the time:

The first thing you want to check is your thermostat. (That’s where a hvac technician would start in troubleshooting.) With the thermostat setting set to “ON”, the blower will run all of the time. It’s pretty much just a fan blowing air constantly.

What’s the fix?
Simply set your thermostat’s fan setting to “AUTO”. This will cause the constant blowing of cold air to cease and your furnace will only blow warm air whenever it is prompted to run.

2) Your furnace has overheated

If the furnace is blowing warm air but then starts to blow cold air and then it actually stops running altogether for a period of time:

It’s very probably that your furnace is overheating. If this is the case then the furnace limit switch caused the burners to turn off. Then, the furnace blower continues to run to cool it off. Once the furnace is cooled off the blower will stop running. This describes the process above: the furnace blows warm air but then cold air and finally it stops running altogether.

What would be the culprit of a furnace overheating? More than likely it would be the air filter.

A dirty or clogged air filter will block airflow. The furnace will run constantly trying to heat your home or business to the set temperature but if the filter is clogged or dirty it hinders the airflow. Thus the furnace is running much more than it should be and it is overheating.

The fix is simple. Simply change the air filter and see if the problem persists. You can do this yourself or you can call your local hvac service company and have them do it for you.

3) Your pilot light is extinguished

The pilot light might be out if your furnace is only blowing cold air.

Check your pilot light and if it has extinguished:

Simply relight the pilot light. If the pilot light relights and stays on then you’ve likely found and fixed your furnace problem.

If you are not able to relight the pilot light then ensure that your furnace’s gas valve is open. The valve handle/switch should be inline and parallel with the gas line itself. If it is perpendicular to the gas line, then it is closed. If this is not the problem then make sure your pilot is clean and not dirty or obstructed.

Again, if you don’t feel comfortable doing this yourself, call your local hvac service company for assistance.

Furnace blowing cold air, still?

We hope this has helped you! Are you still having problems with your furnace blowing cold air? Or did you not find your problem listed? No worries! We perform furnace repair services.

Call Cagle Service today, 731-300-1030, and give us more details about your problem, and we’ll get back to you ASAP!

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