Why Is Cold Air Coming From Vents When Heat Is Off? The Easy Fix

The warm air gently puffing from the air registers around your home helps keep it toasty and comfortable in the winter months. 

However, you might notice cold air coming from vents when the heat is off. And most likely, you’re wondering if there is something wrong with your furnace and how much it will cost to fix it. 

Thankfully, there’s usually one primary culprit for the cold air bellowing from your vents. And, it’s usually an easy fix that won’t cost you a dime. 

If you are dealing with cold air coming from the vents when the heat is off, continue reading to learn the quick and easy fix! 

a person inspecting why cold air is coming from events when heat is off

The Reason Cold Air is Coming From Your Vents When the Heat is Off

Cold air coming from vents when the heat is off is usually due to a simple setting on your thermostat. Generally, when this issue is happening, the “Fan” setting is set to “On” instead of “Auto.”

When the fan is set to “On,” the furnace’s blower motor (fan) runs constantly. This means the fan pushes air through the ducts and into your rooms, even when the furnace isn’t providing heat. 

So, even when the furnace is not producing heat, the fan will blow air into your ducts that aren’t heated. The air it blows is recirculated from other areas of your home like the basement, crawlspace, or attic.

This recirculated air may feel cold since it is not heated and comes from cooler areas of your home. While cold air might be pleasant in sweltering summer months, it isn’t desired in sub-freezing temperatures. 

Note: To stop cold air from blowing from your vents when the furnace is off, all you have to do is switch the fan setting from “On” to “Auto.” That’s it! We told you it was simple. 

You might also notice a strange fluctuation in temperature near the air vents when the furnace is cycling on and off. As the furnace cycles, there might be an initial puff of cold air before it’s replaced by warm air.

When the furnace turns off, the blower will run a little longer after the heat shuts off. The air might feel cold then too. 

In this case, the initial puff of cold air before and after the furnace kicks on is entirely normal, and you won’t need to do anything to fix it. 

Is Stopping Cold Air Coming From Vents When the Heat Is Off Really That Easy?

a person changing the fan setting of the thermostat

Yes. Thankfully, stopping the cool airflow from the vents while the heat is off is usually an easy solution. Simply change the “Fan” setting on your thermostat from “On” to “Auto.” 

By changing the fan setting, you essentially tell the furnace’s blower motor to run only when the furnace generates heat during its heating cycles (the furnace usually cycles between 3 and 8 times per hour). 

If the fan is set to “On,” air will only come from the vents when the furnace actively burns natural gas to provide heat. 

On the flip side, the fan won’t push air through the vent when the furnace is off, as it only runs with the furnace. 

In addition to fixing the issue, switching the fan to “Auto” will also lower your monthly energy bills since it will only operate when the furnace is actively running. 

What to Do if This Fix Doesn’t Work? 

If the thermostat fan setting wasn’t the issue or didn’t seem to correct it, you may have a more significant problem. In that case, the best thing to do is call an HVAC technician. They have the knowledge, experience, and skills to properly isolate and fix the problem. 

Once they determine the issue, they can advise you on the best course of action and move forward with a repair. In addition to fixing the problem, an HVAC technician can also make sure your system is up to par and running efficiently. 

Alternatively, if your furnace is blowing cold air when the heat is on, check out our guide here

If your furnace isn’t running as it’s supposed to, or you need HVAC maintenance services, we recommend getting a HVAC expert out to check over your system.

About The Author

Jonathon is a mechanical engineer with over ten years of experience in the HVAC industry. He has hands-on experience with all types of HVAC systems.

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