Why Is My Furnace Blowing Cold Air?

Notice that the air coming from your vents is cold when it should be warm? That’s no good.

Your furnace can blow cold air for a variety of reasons. Some of those reasons have a simple (and inexpensive) fix, and others require a professional to diagnose and repair.

A few of the most common reasons your furnace may be blowing cold air include...

• The thermostat is on the wrong settings
• Your furnace has overheated
• Your ductwork is leaking
• There’s an issue with your blower motor

The only way to know for sure what’s wrong with your furnace is to have a professional assess your system and determine the root cause.

However, by reading through these 4 common furnace issues, you may be able to at least get a better idea of what’s going on with your furnace and what you can do to get it blowing warm air again.

Your furnace may be blowing cold air because the thermostat is on the wrong settings.

There are two key settings that can make your furnace blow cold air:

1. The temperature setting
2. The fan setting

The temperature setting:

During the winter, your furnace needs to be set to heat. If it's not, it will likely not turn on often, and when it does it will blow cool air.

The fan setting:

The fan setting needs to be turned to AUTO, not ON.

If the thermostat fan setting is ON, the furnace will blow air continuously, even when the air hasn't been heated. On the flip side, when your thermostat is set to AUTO, it only blows air that's been heated.

So, if your thermostat is ON, that may be why you notice cool air coming through your vents.

Another reason your furnace may be blowing cold air is because it has overheated.

If your furnace starts to overheat, there's a safety switch that will shut your furnace off to prevent the internal components from becoming damaged.

To cool your furnace down, the blower will continue to blow cool air over the heat exchanger and other parts of your furnace, which is why you may notice cool air coming from your vents.

There are a couple reasons why your furnace can overheat, but a couple of the most common include:

• A dirty air filter
• Closed or obstructed return or supply vents

A dirty air filter:

On average, you should replace your air filter every 1-3 months. If your air filter becomes clogged, it can prevent the airflow to your furnace, which can cause your furnace to overheat.

Closed or obstructed return or supply vents:

It’s important that you open all return and supply vents and don’t block them with furniture or other obstructions. All return and supply vents need to be open and unstructured for your system to properly circulate air and keep your furnace from overheating.

If you notice that the air coming from your vents is continuously cooler than it should be, you may have leaky ductwork.

When there are cracks or leaks in your ductwork, the air that your furnace has heated can be lost to unconditioned areas of your home that your ducts run through, like your attic or a crawl space.

While losing heated air doesn't necessarily make the temperature of the air colder, it can make the air feel colder because there is less hot air coming from your vents.

Another sign that you have cracks or holes in your ductwork is increased energy bills. When your ducts leak, your furnace has to produce more heated air than normal to heat your home. This can have a big impact on your energy bills depending on how extensive the leaks are.

Reach out to an HVAC professional if you think your ductwork is leaking. They will be able to perform an assessment of your duct system and determine if you need to have your ducts sealed or potentially replaced.

If you only notice cold air coming from your vents when your furnace first cycles on, there could be an issue with the blower motor.

Typically, the furnace burners will warm up completely before the blower turns on. This ensures that the blower is only blowing warm air through your duct system.

However, if your blower turns on before the furnace burners are fully heated, your furnace will blow cold air into your duct system.

There are few issues that can cause the blower motor to turn on prematurely, including:

• An incorrectly wired thermostat
• Issues with the control board
• Faulty fan control switch

If you’ve tried the above DIY fixes and still can’t seem to get your furnace to blow warm air, it’s time to reach out to a professional.

At Advantage Air, we’ve been working with Tucson homeowners for over 30 years, so no matter what’s going on with your furnace, we can accurately diagnose the issue and repair it in no time.