Why is my Furnace Blowing Cold Air?

Posted by: Mas Broto
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Why is my Furnace Blowing Cold Air

Is your furnace blowing cold air instead of sufficiently heating your home? There are many reasons why this might happen, and you might be able to address some repairs on your own while others will require a professional. Keep reading to learn the common reasons why your furnace only blows cold air, including some quick troubleshooting tips.

When your furnace is blowing cold air, you want to make sure that they are fixed as soon as possible. Remember that the first time you turn on your furnace, cold air will blow out for a few minutes as the air already within the system escapes. It is usual for the furnace to blow cold air for a while until it is warm.

If after a while of operation you notice cold air continues to blow through your vents, try this quick furnace troubleshooting before calling a pro.


Ensure your thermostat is on heat mode and set it at an appropriate temperature. This is a common source of initial furnace troubles people tend to overlook.

Air Filter

In order to run effectively, furnaces require regular changing of the air filter. Professionals recommend changing your furnace filters minimally every three months, though some areas may require a more frequent change.

Air filters are an important part of furnaces that can contribute to poor heating performance. If you haven’t changed your air filter lately, now is the time. A clogged filter can block airflow and, in some cases, cause the burners to shut down so that they don’t overheat.

Pilot Light

In an older furnace, the standing pilot light may have gone out and needs to be relit. Newer furnaces have an electronic ignition system that only lights when the thermostat calls for heat.


Burners that are dirty and become clogged can also cause the fan in your furnace to blow but without any heat.

Flame Sensor

Dirty flame sensors may also be the reason why the furnace blows cold air, as they cause heated air to go cold while the gas burner is kept from staying lit.

Fuel Supply

For any heating system to operate properly and produce heat, the fuel supply must be available and working. So for a gas furnace, issues like a faulty gas valve or thermocouple problem can keep the fuel supply from the burners, thus keeping the system from heating.

Call for a professional HVAC Technician to assess the problem when in doubt. The sooner you can figure out what’s wrong, the sooner you can have your furnace repaired and the heat back on. Annual maintenance is one way to prevent many furnace problems at the start of the season or during the coldest time of year, including lack of heat.

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Mas Broto

Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.

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