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How to Figure Out Why Your Furnace is Blowing Cold Air

Cold house? Find out if your furnace is to blame! These tips will help you troubleshoot issues with a furnace blowing cold air.

why your furnace is blowing cold air

Staying warm in our homes in winter is crucial, but what do you do when your furnace is blowing cold air instead? Before you start cranking up the thermostat, take the time to do a little furnace troubleshooting. These six tips will help you discover problems that could be costing you heat and money!

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I live in Seattle, where winters are pretty moderate with temperatures hovering in the high 40's (with rain. Lots of rain!) But every once in a while, our warm blanket of cloud cover disappears and the clear sky makes temperatures drop below freezing. I want to make sure our furnace is running in tip top shape, so our family stays toasty warm.

One modern convenience that we all tend to take for granted is our furnace. We set it and forget it, confident that the furnace is working to keep those freezing temperatures at bay on the other side of our door.

But, even the very best heating units have a finite lifespan. Knowing the clues to look for and doing a little furnace troubleshooting can ensure that you get a jump on possible problems before you and your family are left shivering under your blankets.

Check the Thermostat

If you notice that temperatures in all areas of your home are steadily dropping, don't panic! It could simply be a problem with the thermostat, which is a much easier fix.

Change the Batteries

You may need to replace batteries in your thermostat. This will be obvious if the screen is dim or off. Just pop it off the wall and pop in some new batteries.

thermostat with dim screen on the wall

Check the Fan Setting

Is your fan set to ON? This will constantly circulate air throughout the home, even when the furnace isn't currently running. This can make it feel like the furnace is blowing cold air.

Change the fan setting to AUTO so that it will only move warm air directly from the furnace into your rooms.

adjusting the thermostat fan setting to AUTO to stop the furnace blowing cold air

Replace the Thermostat

If you have a really old thermostat, it may be time to replace it with a new one. The sensors or electronics inside will stop working properly over time, just like any other electronic device.

Take advantage of modern technology and invest in a fancy new thermostat like the Nest. It can be easily programmed from your phone, and it can learn your heating habits and adjust the temperature accordingly, saving you money. It can also alert you to problems like a low battery before you notice a chill!

modern thermostat with wall plate

Insulate Heating Ducts

If there are differences in temperature between rooms or areas of your home, it may indicate that there is a problem with your ductwork that needs to be addressed.

In our house, our second floor could get downright frigid at times. We learned that we were losing a lot of heat from the ducts that pass through the colder unfinished part of the basement. Wrapping them in duct insulation kept the hot air flowing to the upstairs rooms.

insulate heating ducts to prevent your furnace from blowing cold air

While this may be an easier project to tackle when the home is being built, just adding a few rolls of insulation to visible ductwork can make a big difference!

Change the Air Filter

When was the last time you changed the filter on your furnace? If your filter is clogged from years of dust, fresh air can't get to your furnace. This makes it struggle to work properly, and it could start blowing cold air instead of hot.

replacing the furnace filter

Locate the access door for the furnace filter, and slide out the filter. The new filter should be identical to the old one, with the arrows indicating air flow pointed in the same direction. Slide the new filter in place, and close up the access door.

If your furnace is still blowing cold air after completing these steps, you may need to call in an HVAC professional. If the filter was clogged enough to cause the furnace to overheat, it could trigger the limit switch to shut it down. It may need to be replaced before the furnace will work properly again.

Whooshing Sounds and Other Auditory Clues

Has your furnace started making strange noises lately? An obvious whooshing sound when your heating unit fires up can indicate that it's burning too rich and is in need of a tuneup. Not only does this create extra wear and tear, it also wastes gas. Getting this problem taken care of can often make a noticeable difference in your heating bill.

furnace tune up

If you hear a high-pitched squealing sound when your heater starts up, it can be an indicator of a problem with the bearings in your blower motor. This is something that should be taken care of quickly, as it can cause your motor to freeze up. Frozen motor = frozen house! An overheated blower can also become a fire hazard if not dealt with promptly.

Visual Clues of Possible Furnace Problems

Visual clues can also offer evidence during furnace troubleshooting. If you check your burner and see anything other than a steady blue flame, it can indicate troubles ahead.

blue furnace flames

This is definitely one of those times when you'll want to consult a trained heating and cooling professional. At the very least, flames of other colors mean that your furnace isn't operating as efficiently as it should.

Smelling Gas - Even a Little Bit

If you smell gas, even slightly, it's very important to check it out. A gas leak will effect the efficient operation of your gas furnace. But more importantly, it can be a very serious health hazard to you and your family. Gas leak detecting equipment can help track down the location of gas leaks so they can be repaired quickly and efficiently.

As a preventative measure, you can install a combustible gas alarm in the area near your furnace. This will give you peace of mind that you will be alerted to gas leaks, even as you sleep.

Know the Age of your Furnace

Furnaces are designed and built to last many years, but none of them keep running forever. If your particular heating unit has reached or passed the manufacturer's warranty period, you may not be getting all of the heating productivity that you're paying for.

HVAC experts can do much to prolong the life of a furnace, but there will come a day when it's more expedient to replace a unit than to keep pouring money into repairs.

Track and Compare Heating Bills Over Time

If you begin to notice a marked increase in annual heating costs over several heating seasons, your furnace may have lost some of its efficiency. This is another one of those times when you should call a heating and cooling specialist and discuss your concerns.

comparing heating bills over time

No furnace lasts forever, but, just like your car, doing a little furnace troubleshooting can keep it running longer and more efficiently. When your furnace is working properly, it will keep you and your family warm and toasty all winter long.

Check out these other home maintenance articles!

Is your house always cold? Do a little furnace troubleshooting to see what the problem is. | home improvement | home maintenance


Friday 10th of February 2017

These are some great tips! And I find myself questioning if our furnace is working properly all the time so this really helps me out! Thanks for sharing!

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