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Why Is My Furnace Blowing Cold Air?

Featured image of the blog title "Why Is My Furnace Blowing Cold Air" with a background of a cold woman because of blowing cold air of the furnace

Is your furnace blowing cold air, or maybe it is having problems keeping your house warm.

People are more likely to notice issues with their furnace as temperatures begin to drop and we transition from air conditioning to heating. It might be running just fine when you suddenly realize that the air is not warm. As a matter of fact, the air might be downright cold.

For most of us, the question remains; why is my central heater not blowing hot air? You are probably wondering what the problem is and whether you should be alarmed.

A heater that is blowing cold air can be a cause for concern, particularly on a chilly day.

Since several possible reasons can cause it to blow cold air, it’s hard to give advice without additional information, which is why we will share what we know about this issue. You might be able to complete some of the repair work, but if the scenario is a little bit more technical, you should contact a professional heating company Near You to diagnose the issue and fix it.

Help, My central heat is blowing cold air!

First, Check your thermostat


You should check the thermostat setting if it does not blow cold air at all times, yet the fan keeps running. When trying to determine the cause of this particular issue, any tech will start by checking the thermostat,  and so should you. Your blower will keep running if the thermostat’s fan is set to ON, even when the unit is not heating the air in your home.

However, there’s an easy solution. You only need to turn the thermostat’s setting to AUTO. Flip the switch from ON to AUTO. Once you set it to AUTO, the heater will blow only warm air into your home.


If your furnace blowing cold air instead of heat, it could have overheated. If so, the limit switch, a featured safety device, probably turned the burners off. But the fan continues to run, cooling the furnace to a safe level.

A dirty air filter is the most common cause of overheating since it blocks airflow. As a result, your furnace will run longer to heat your home, causing it to overheat. Fortunately, you can solve this problem by changing the air filter. Once you’ve changed the air filter, check to see whether your heater starts blowing warm air only.

Remember, constant overheating might damage your heat exchanger, and this will call for a replacement. Don’t ignore this problem because replacing the heat exchanger is expensive.

The pilot light is out

If your gas furnace is not blowing hot air, then the pilot light might be out. Check to confirm, and try the following solutions if it is out.

    • Relight the pilot light. Check the instructions on how to ignite the pilot light. If you don’t find the instructions on the heater itself, try the user’s manual that came with your unit. Once you’ve relit the pilot light, wait to see if the flame stays on. If it does, then all is well.
    • If the pilot is not lighting, make sure gas is flowing into the furnace. Find out whether the gas valve switch is on. If the switch is on, then the pilot light is probably dirty. Cleaning the pilot light helps to ensure gas comes through.
    • If the pilot lights but does not stay lit, then you probably have a problem with the thermocouple. In this case, you’ll need to adjust or replace the thermocouple. Although a do-it-yourself replacement is possible, it might not be easy if you are not familiar with the work involved. Contact a professional technician if you are not comfortable with the replacement.

    Dirty Flame Sensor

The gas burner will not stay lit,  you have a dirty flame sensor. Your furnace is bound to cycle on and off if this is the case.

Not enough gas

If you have a clogged gas supply line, it will not have the required amount of gas to provide warm air. In this case, it’s possible for your furnace to lock down for safety reasons. This requires a professional heating repair company.

Clogged condensate drain lines

Clogged drain lines can prevent the burner from lighting, especially when it comes to the newer, high-efficiency models.

Is Your Heating Unit the Wrong size?

Size also matters. If the furnace you have installed is too small for your home, then it won’t be able to heat your entire house efficiently. On the other hand, units that are too big are known to cycle on and off due to lack of power or confusion in the mechanics.

If the job is too technical or you are experiencing any other furnace-related problems, feel free to call us for help.

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