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Why is my furnace blowing cool air?

Why is my furnace blowing cool air?


  1. The Thermostat is Set to ON


This is one of the most common reasons why you may be feeling cool air coming from the vents instead of the expected warm air


  • What would be the reason for this?

Generally, thermostats have two fan settings which are ON and AUTO.

When the user has the setting on AUTO the fan only operates when the furnace burner is on resulting in the fan blowing warm air through out the home.

When the furnace burner turns off the fan also turns off.

However, when you have the fan set to the ON setting, the fan blows nonstop, no matter if the burner is operating or not.

The situation you are left with is the fan blowing air constantly that has not been warmed.

In other words, if the thermostat has not been triggered to turn on the furnace then you will experience cool air blowing out of the vents throughout the home.

This could give you the false sense that your furnace is not working properly.


  1. The Thermostat Is Not Working Correctly


Nowadays most thermostats are computerized and just like computers they might have encountered a problem that requires the system to be restarted.

When you restart it, and it comes back on fully this might correct the cold air problem for you.

The next option would be to check the battery.  If the thermostat uses a battery, the level of energy the battery has left might be too weak to power the system.

Check the make/model of the suggested battery and replace it to see if it corrects the problem.

It would also be wise to note the date you replaced the battery to get a gage on how long they last or when the next time you should expect to replace it.


  1. The Pilot Light Is Out

The furnace can only put out cold air if the pilot light has gone out because the burner will not light.

To understand it better it would be the same scenario if you had an older gas water heater with a pilot light and if that pilot light went out you would experience cold water or know that you would get a cold shower if you took one.

The thermo-coupler on the furnace could need replacing if there is trouble keeping the pilot light on the furnace lit.

To replace the thermo-coupler, it is not that difficult of a job to do but some homeowners may not be that comfortable to do so.

Therefore, it is good to know that here at A1 we have professionals that can handle any project when it comes to plumbing, heating, air conditioning & refrigeration(commercial) services.

If your furnace is blowing cold air for any reason and you do not want to take a chance on fixing it on your own, then you can:

CALL TODAY@ 904-475-0093.


  1. The Filters Are Dirty

To operate at maximum efficiency your furnace needs the ability to breath good, clean air.  It can do so thanks to the air filter that works hard to provide that good, clean air.


When general maintenance with the air filter is forgotten or neglected such as replacing them when they are due to be replaced it causes the filter to become clogged and not enough fresh air reaches the furnace.

The furnace’s heat exchanger can overheat because of this so to prevent damage to your furnace the burner will shut down.

However, to bring the temperature of the burner down to an acceptable level, the fan may continue to blow for a short time.

Therefore, you might feel cooler air blowing throughout the house.


If it is a furnace that burns oil it will have an oil filter and if this filter becomes clogged it might cause the burner to have trouble firing period.


  1. The Burner Is Dirty


If the filters are unable to do their job because of neglect, there will be a good chance that the burner has had enough time to accumulate a lot of grime.

Dirt or grime on the burner could prevent it from firing properly.



No matter the issue A-1 is here to cater to all your needs when it comes to plumbing, heating, air conditioning, and refrigeration services.

Don’t forget we do remodels/renovations as well!!




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