Why is My Furnace Blowing Cold Air Instead Of Heat?

You’re inside your home, beginning to shiver as the temperature outside dips lower and lower. So you go to turn on your furnace, looking forward to that warm air.

Instead, you’re greeted by the furnace deciding to blow cold air. That’s not right – so what’s going on?

1. Your Furnace Isn’t Warmed Up Yet

That icy blast of cold air can stir up a sense of panic, particularly if temperatures are going to drop later in the day.

If this is the first time you’re turning on your furnace for the season, make sure to wait several minutes. It’s like bringing a kettle to boil – it doesn’t happen instantly. Instead, your heating cycle needs time to get rolling before it starts blowing hot air.

After approximately 10-15 minutes, start moving down this list if your furnace is blowing cold air.

2. Your Thermostat is Set Incorrectly

Thermostats make our lives so much easier. They’re also the first place you should look if your furnace isn’t working properly.

It’s easy to have your thermostat set incorrectly, particularly when the seasons change from summer to fall and we turn on our furnaces for the first time. If you can feel the furnace blowing through the air vents but it’s cool air, maybe you set it for the summer and never changed it when you put your air conditioning unit away for winter!

You want to make sure that your thermostat setting is ‘Auto,’ not ‘On’. When it’s set to ‘on’, the fan on your furnace will blow even when your furnace isn’t on. When it is set to ‘Auto’, your furnace and fan will come on at the same time, as intended.

There’s also a possibility your thermostat isn’t working properly.

3. The Furnace Filter is Dirty

Air filters catch dust and debris we generate in our homes—that means they need to be changed on a regular basis.

An overly clogged air filter will limit airflow to your furnace and could cause it to overheat and turn off. Then the furnace blowing cold air is all you’re going to get!

This is something you can check yourself – just make sure your furnace is turned off before you look at or remove the filter from the air handler. Make sure your air filter is changed every 90 days. If you have forgotten about it, now is the time to get rid of that dirty air filter! This is a really important, low-cost maintenance that can prevent your furnace’s heat exchanger from getting damaged, which is a very expensive furnace repair bill.

4. Your Furnace Has Overheated

When your furnace overheats, there’s a safety mechanism that actually will shut your furnace down. So not only will your furnace be blowing cold air temporarily, but it’ll actually shut off.

There are a few reasons your furnace could be overheating (besides a clogged filter):

Dirt buildup – if your filter was clogged, chances are dirt and debris worked their way into other parts of your furnace. If that dirt is in moving components, like the blower, it can cause your furnace to overheat.

Mechanical failure – as a furnace experiences wear and tear, it’s possible for your furnace to overheat because one of the moving parts isn’t performing correctly (or at all). This may be the source of your furnace problems, particularly if you have an older furnace.

Age – as a furnace ages, it stops performing as well. Furnaces usually last around 15 years. Even with the best preventative maintenance, it won’t last forever and could start overheating if certain parts can’t perform. Typically the furnace burner itself, the flame sensor, or the gas supply pipe are to blame.

5. The Condensate Line is Clogged

High-efficiency furnaces have condensate lines that move water away from the furnace.

A clog in the condensate line will prevent your furnace from igniting. No ignition means only cold air coming through your vents. There could also be an issue with your condensate drain lines, but an HVAC technician will be able to tell you exactly what the problem is.

6. The Pilot Light Keeps Going Out

This is mainly for older furnaces. Many new models of furnaces have an electric pilot light that only turns on when needed- older ones will have a pilot light on continually from the gas line. If you are comfortable doing so, you can relight it by following the instruction kit that came with the furnace (always turn off the gas before doing so).

Pilot lights can be very dangerous to replace, especially on a gas furnace, so please be careful to read the booklet that came with your heating system. It may also be a faulty thermocouple (the sensor that controls the gas and ignition) which needs replacing. If you are concerned about handling anything on your own, give us a call.

7. There’s A Problem With The Gas Supply

If your pilot light is going out instantly or not lighting at all, it may be an issue with the gas supply. If this is the case, we have good news: Your furnace is designed to shut off if there is an issue with the gas supply.

There might be an inadequate gas supply in your tank, but it might also be an issue with how the gas gets to your furnace. If your pilot light doesn’t light at all, it may also be the gas valve. This is not an issue that you can do on your own; you need to call a professional.

8. The Air Ducts Are Leaking

If you have holes, disconnections, or leaks in your air ducts, then all the hot air is escaping before making it through your vents. Sometimes this can be due to age. Other times it can be due to a small animal biting or clawing at them. Leaking ducts have more of an effect than you’d think, and duct sealing would fix this problem—either with tape or new pieces depending on the damage. Have a professional do an inspection to find the problem areas.

Have Husky Come Take a Look

It’s safe for homeowners to try fixing the thermostat and air conditioner. But if your furnace is still blowing cold air after you’ve tried those, call us to have an hvac technician help you out – don’t try to repair your furnace yourself.

The friendly professionals at Husky can diagnose and repair the problem on any make or model of furnace. We can also perform preventative maintenance after the repair is complete to prevent this from happening in the future.

FIX YOUR FURNACE THAT’S BLOWING COLD AIR