Heating & Air Conditioning Expert with over 25 years of experience

Hours: 8:00AM to 5:00 PM  /  M-F
Phones Monitored 24/7

Dallas County:214-382-0780
Ellis County: 972-775-6686

Why is my Furnace Blowing Cold Air?


When the chilly weather finally arrives, and you must turn on your furnace for the first time after many months of non-use, the last thing you want to find is that it’s not working. Or, even worse, you discover that it’s blowing cold air! It can be incredibly frustrating to have to deal with a malfunctioning furnace right when you need it the most. Still, there’s no reason to panic.

As exasperating as this situation may be, the solution may be a simple fix. What follows are some of the most common reasons a furnace may blow cold air.

The Furnace Hasn’t Warmed Up

If you get a blast of cool air when you first turn on the furnace, but after a couple of minutes the air feels warm, that is nothing to be concerned about. It’s normal for cool air to emerge from the vents at first because the furnace has to warm up. Think of it in the same way as turning on a hot water faucet; you’re going to get cold water at first. The same effect happens with your furnace. It must push out the cold air from the vents before the warm air can come. Of course, if warm air doesn’t follow after a few minutes, something else might be going on, and that’s time to schedule a service call.

Your Thermostat is Set to “On”

If there’s a constant flow of cool air coming from your furnace, check your thermostat to see if the unit’s fan is set to “on” or “auto.” Chances are, your thermostat’s fan setting is set to “on,” in which case your furnace blower will constantly run even when your furnace isn’t heating the air. By switching the thermostat to “auto,” the fan will only blow when the furnace is heating the air.

The Flame Sensor is Dirty

Pilotless ignition furnaces use a flame sensor to keep the furnace burning once it starts. If the flame sensor is dirty, your furnace will turn on and begin heating but then turn cold relatively quickly. If you’re familiar with furnace components, you can clean the flame sensor yourself, which should restore your furnace’s heating function. Or, you could enlist the services of an HVAC technician to clean the sensor for you.

The Pilot Light is Out

If your gas furnace is older and it’s blowing cold air, chances are its pilot light has gone out. If you’re comfortable doing so, just follow the manufacturer’s instructions for how to re-light it safely. Alternatively, you can call your local utility company or an HVAC technician to make sure it is lit safely. Once it is lit, if it doesn’t stay lit, it may need some routine maintenance from an HVAC professional.

The Air Filter is Clogged

Dirty air filters are a problem because they limit airflow into your furnace. Restricted airflow can cause your furnace to run longer to heat your home until it overheats. When your furnace overheats, you will only get cold air. The solution is to replace your dirty air filter with a clean one. Once airflow to the furnace is no longer blocked, your furnace will be less likely to overheat and should function normally.

Still having problems? If your troubleshooting efforts don’t resolve the issue, something more serious may have gone awry. That’s when you should call Speedy Electric and A/C to help sort things out.

Contact Information

Phone Numbers:
Dallas County – 214-382-0780
Ellis County – 972-775-6686

Hours: 8:00AM to 5:00 PM  /  M-F
Phones Monitored 24/7

Our Office Location:
1861 Shady Ridge
Midlothian TX 76065

Email Us:
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We pride ourselves on being a one stop shop that is able to meet all of our client’s needs. Our goal is to provide the highest quality design, air conditioning service, and installation, on schedule, and on budget along with outstanding customer service. We understand that time and cost are crucial and we strive to go above and beyond our client’s expectations.