If you’ve noticed that your furnace isn’t heating your home properly but is instead blowing cold air into your home, you’ve got a problem.
Your furnace could be blowing cold air because:
- Your thermostat is on the wrong settings
- Your furnace has overheated
- Your ductwork is leaking
Below, we’ll look at these issues in more detail and provide recommendations on how to get your furnace blowing warm air again.
Rather have a Colorado pro look at your furnace ASAP? Contact the Cooper Green Team. We provide fast, 24/7 furnace repairs in the Denver and Colorado Springs areas. We’ll get your furnace up and running in no time.
Cause #1: Wrong thermostat settings
The simplest reason your furnace could be blowing cold air is that your thermostat is not on the right settings.
You’ll want to make sure that your thermostat is set to HEAT not COOL. If your thermostat is set to COOL, your furnace will not heat the air.
HEAT vs COOL setting on your thermostat
Next, you’ll want to check that the thermostat is set to AUTO not ON. If the thermostat is set to ON, the furnace will blow air no matter what—even if the furnace is not heating the air. When the thermostat is set to AUTO, the furnace will only blow heated air. 
ON vs AUTO setting on your thermostat
Cause #2: An overheated furnace
While you may think that an overheated furnace would create hotter air, it actually creates cold air. Why? Well, your furnace has a safety switch that will shut down the heating elements of your furnace if it notices that your furnace is starting to overheat.
Once the safety switch shuts off the heat exchanger (the part that heats your home’s air), the furnace fan will continue to blow cold air over the overheated heat exchanger in order to cool down the furnace. Once that happens, you may feel cold air coming from your vents.
The main two reasons your furnace may overheat are:
- Dirty air filter: If your air filter is dirty, it will restrict airflow to your furnace, which can cause your furnace to overheat. The less cold air enters the furnace, the more likely the heat exchanger will overheat.
To fix this problem, replace your air filter once it starts looking dirty. You can prevent your furnace from overheating by replacing the filter monthly.
Clean (left) vs dirty (right) air filter
- Closed vents: When too many vents are closed, your furnace won’t be able to pull in enough cool air to blow over the heat exchanger. If that happens, the furnace can overheat and shut down. To prevent this, you’ll want to keep all of your air vents open and unobstructed—even in rooms that don’t need to be heated.
A return vent
If your furnace is still blowing cold air after you’ve replaced your air filter and opened all your vents, it’s likely that there is a bigger problem like a blocked exhaust vent or a clogged fan motor. You’ll need to contact a professional to diagnose the problem and fix your furnace.
Cause #3: Leaky ductwork
If your home’s ductwork has major leaks, you may feel cold air coming from your vents even if your furnace is in perfect condition.
When there are leaks in your home’s ductwork, a significant amount of the air your furnace heats can be lost in areas of your home that don’t need heating, like the attic. This also means that your leaky ductwork is pulling in the cold air from the attic, making the heated air coming out of your vents colder.
If you think leaky ductwork may be your issue, you’ll want to contact a professional to inspect your ducts. If your ducts are leaking, a professional will recommend either sealing or replacing the damaged ducts.
Hot air leaking into the attic makes the air coming out of your vents feel colder
Want affordable furnace repairs? Contact Cooper Green Team
From flat-rate, upfront pricing to flexible financing options, we want all homeowners to be able to afford high-quality furnace repairs so you aren’t stuck with cold air during the Colorado winter.
We provide furnace repairs in the Denver and Colorado Springs areas.
Luke Cooper is the General Manager of the Cooper Green team and son of Gary Cooper, owner and CEO of Cooper HVAC. After years in the field, Luke took his talents to management and has helped thousands of Colorado homeowners during hot summers and frigid winters. His decade of experience in the field and guiding the company makes him one of the most knowledgeable individuals in Colorado on HVAC, plumbing, electrical and other home services.
