Why Is My Furnace Blowing Cold Air?

It is easy to get sick of cold air at some point during the long Minnesota winter. But it is downright maddening when the cold air is coming from your very own furnace! Several issues could cause this, which unfortunately makes it somewhat of a common problem. If your furnace is getting power, running continuously, and pushing out air yet still not achieving the temperature set on the thermostat, then you may have a problem.

You are in the right place. In this post, we’ll walk you through the most likely issues causing this and outline what troubleshooting you can do on your own.

Thermostat Setting:

Your thermostat has two settings for the fan: “On” and “Auto” — the fan will run continuously when set to “On,” even though it is only blowing heated air part of the time. Turning the thermostat to “Auto” will resolve this by only running the fan when the thermostat is calling for heat.

Furnace Overheating:

It seems counter-intuitive but yes, your furnace can actually overheat. This is not something to ignore as it can cause serious (read: expensive) malfunctions to other parts of the system such as the heat exchanger. If your furnace blows hot air, then cool air, but then stops blowing air all-together is a tell-tale sign of overheating.

What’s happening is that your furnace’s limit switch, an important safety feature standard on all furnaces, is sensing a problem and turning the furnace’s burners off. The furnace’s fan will continue to run in an effort to cool things back down to a safe range. An extremely dirty air filter is the probably culprit in this case. When airflow is severely restricted at the filter, it will cause your furnace to work extraordinarily hard to heat your home. It will overwork itself in its struggle to reach the target temperature. This expedites the wear and tear on the unit — yet another reason to change your filter regularly!

More uncommon is an improperly sized furnace. If a furnace is too small for the space it is trying to heat it will overwork itself. This should be addressed immediately by a professional.

There is not much more a homeowner should attempt to do on their own aside from changing a thermostat setting or a dirty air filter. An experienced and confident homeowner might feel comfortable relighting the pilot light (which we’ll cover next). Beyond that, we strongly recommend your next step be to call Owens for assistance. HVACs and furnaces pose serious danger to someone not properly trained.

We’ll continue on with common causes to give you an idea of what could be wrong, and what a technician will look for first.

Problems with the Pilot Light:

Did the pilot light go out? If so, this is why you aren’t getting heat. The furnace can’t ignite its burners, meaning it can’t heat your home either. Restoring the flame should resolve the problem.

Again, a very experienced homeowner may be capable of relighting the pilot light. If you are successful, make sure you observe it for another five minutes or to make sure it stays lit. If so, great! The problem should be resolved. If not, it likely means there is a problem with the fuel line, corrosion, or otherwise an inadequate gas supply. The thermocouple or pilot itself may also be dirty or need to be replaced. These tasks should all be inspected and performed by a professional.

Drain Lines Clogged:

Most newer furnaces have condensate lines that drain any water created during the heating process. The furnace has a safety switch that will halt operation when there is a clog. In some models, there is a safety switch that will shut down the entire unit. In others, it simply shuts down the burners while the rest of the unit continues to run.

Duct Issues: 

If you have serious duct issues you may be losing so much hot air out of holes and gaps that it feels cool by the time ti reaches the vents. Owens mechanics can check your ductwork to ensure it is adequate.

Part Failure:

There are several parts tat could be malfunctioning, misfiring, or not sensing correctly, all of which could cause your furnace not to produce heat. If part failure is suspected, Owens technicians will perform a comprehensive diagnosis of the system to uncover which part(s) is causing the trouble.

Thermostat Installation:

Please advise the technician if you have replaced a thermostat recently, moved the thermostat, or otherwise done any electrical work within your home. It is possible that an incorrectly installed thermostat would cause problems with heating the home.

Take action quickly if you suspect a problem with your heat. Check the thermostat, and then change your filter. If the problem persists, it’s time to call a professional immediately.