Your furnace is blowing cold air, and it landed you on this page to try to diagnose and fix the issue.
We’re not going to waste your time. While we can’t diagnose your specific issue over the internet, we can give you a wide range of reasons your furnace might not be working correctly. We’ve seen each of these in our work with homeowners and their HVAC systems.
Then we’ll discuss the fixes you can do yourself, as well as the fixes that will require calling a heating & cooling company so that a licensed technician can resolve the issue.
Reasons Your Furnace Could Be Blowing Cold Air
Here’s a list of the most common reasons your system is blowing cold, cool or lukewarm air.
The Thermostat is Set Improperly
I’ll tell you a quick, embarrassing story about this one. We have one of those programmable thermostats that you can set differently for different times of day or week. It’s extremely useful.
But if you forget to reset it at different times of the year, it could revert to programming for cooler months. And so as the days have gotten cooler this year and we’ve wanted heating, it took me a few days to figure out that the thermostat was just doing its job according to its programming. As a result, we weren’t feeling as much heat as expected.
Some modern thermostats have a lot of functions and can get confusing in a hurry. As the story above suggests, this can even trip up HVAC professionals if they’re not careful!
Your Pilot Light is Out
There are lesser versions of this problem as well, where dirt or debris prevents the light from functioning properly even if it’s not entirely out.
Pilot lights don’t exist in all systems, but in those that have them, they need to be monitored and cleaned regularly, and may need to be relit if they go out.
Dampers are Closed
Your home has vent dampers, and these can be great for funneling warm air to specific parts of the home. However, this can also create airflow imbalances, and much like the thermostat example above, if they’re forgotten, they can harm the heat in your home if left closed.
Air Filter Is Clogged
This is a big one, and is frankly one of the more common reasons we find for poor heating quality.
Your air filter needs to be replaced periodically. How often depends on the type and size of your filter, and other factors like sources of dust, debris and pollutants in the home (smokers, pets, etc.) and how often you run your system.
Some filters should be changed as often as every month. Others can last up to six months of continuous use, again depending on the conditions in the home.
Regardless, a dirty filter is restricting airflow, hurting your system’s efficiency, and could be resulting in cool air reaching the home.
Airflow is Restricted
If air filters and dampers are specific concerns, airflow is the general concern that they’re a part of.
Air flow can become restricted in various ways. We mentioned a couple above, but others exist. Your system’s internal parts can clog much like air filters, and your ductwork is another source of potential airflow problems.
Gas Line Issues
If you have a natural gas furnace, the gas line may not be feeding enough fuel to the system to allow it to fully function. This is a tricky one to diagnose on your own, but monitoring your gas meter when your system isn’t in use, using gas detectors in the home, and checking for gas smells in areas around your system can be quick ways to identify this as a possible problem.
Condensate Drain Line is Clogged
The condensate line allows for moisture exhaust from your system that would otherwise risk harming the system’s internal parts by clogging or rusting them.
Condensate lines can become backed up, restricting airflow and causing your furnace’s burners to shut off in response.
This is a safety measure in many systems that’s actually a good thing to prevent more dangerous problems from occurring, but it still needs to be handled before normal heating operation can resume.
Ductwork Leaking
Another potential source of airflow issues. Ductwork lines are the veins of your system, taking the life-blood (warm air) to every corner of your home.
If they aren’t properly sealed and insulated, you’re losing heat from your ducts. If there are noticeable holes, this heat loss can be enormous.
Internal Part Malfunction
This entry is a catch-all for a lot of other problems that can occur in a system where one or more parts or subsystems cease to work properly, but the blower motor itself continues to run.
This results in cool or lukewarm air coming from your vents, but without actually being heated by the system.
The only safe way to properly diagnose the many possible causes here is to speak with a professional.
Bonus: Heat Pump Blowing Cool Air
Some of the same issues can be true of homes that are heated by heat pumps. But additional considerations apply.
As a reminder, to heat your home, heat pumps remove heat from the air outside your home and circulate it into the home.
This is important to remember, because while heat pumps can heat your home even when it’s very cold outside, at the coldest temperatures, they don’t always heat the air as much as we’re used to.
Air that’s 70 degrees will still heat a home that’s, say, 40 degrees, but it won’t feel as warm as we’re used to coming out of the vents. If this is during the coldest winter days, though, your system may simply be working as intended, as long as it’s able to heat your home even with this lukewarm air.
Fixing Your Cold Air Furnace Issues
Ok, so we outlined the problems. How do you deal with them?
The list below is ordered from simplest to most complicated. The first handful on the list are ones you may even be able to fix yourself, without calling an HVAC professional.
Check Your Thermostat
Is it set properly? Is it reverting to other settings at different times of the day? Does it seem to be accurately gauging the internal temperature in your home?
Worst case, you’ll need to call someone to fix or replace your thermostat, but sometimes it’s as simple as properly setting it for maximum comfort.
Check Your Pilot Light
If you have an older system with a pilot light, it may be malfunctioning or even out entirely. This can cause the air to remain unheated as it circulates through your system.
Some DIY pilot light fixes exist for those willing to do some research, though you can also call an HVAC technician and have them fix your pilot light along with a full tune-up.
Replace Your Air Filter
Never replaced your own air filter? Don’t worry, it’s pretty simple:
ALSO READ: How Do I Change My Furnace Filter? Also How Often and Why!
Check it to see if you have a dirty air filter. And if it is, replace it before the next time you run your heater.
Open Your Dampers
Some sophisticated home systems have dampers that can be controlled electronically, but most are manually controlled at the source. If you have a basement system, several duct lines will have damper switches to close them off. Make sure each of them is open.
Tune-ups, Repairs and Diagnostics
If you’ve done all of the above and you still haven’t solved the problem, it’s time to call a professional.
Some HVAC contractors require a small service fee for a thorough diagnostic on your system to identify all issues. This process can take up to an hour, so it’s not cheap in terms of expert labor!
Best case, you may simply need a cleaning and tune-up of your system. You should be getting yearly tune-ups for your furnace anyway, so this is a great time to get it done.
Worst case, it will be some larger repair, and you’ll want to discuss your options for this with your HVAC contractor.
They may recommend other fixes that will require separate charges as well, including:
- Ductwork insulation
- Ductwork sealing (to plug leaks)
- System upgrades
Depending on the issues you’re facing, any of them may be the best long-term solution.
Tune-ups, Maintenance and Upkeep
Maybe your journey to getting hot air from your system doesn’t require assistance from an HVAC professional. However, this won’t be true forever, particularly if you’re putting off regular maintenance of your system.
Even if your heating system is working, that doesn’t mean it’s operating optimally. Regular tune-ups keep your system at or near its maximum possible efficiency, and more than make up for the cost of the tune-up itself.
Additionally, tune-ups can be required to maintain a warranty, and will add years of life to your system. The good news is that this is an easy step to set up with your HVAC company, and many will offer discounts and benefits to entering into a maintenance program.
Trust Your HVAC Contractor
Don’t mistake this section header; we’re not saying you should blindly trust any HVAC contractor and whatever they tell you.
But you should strive to find one you can trust with your HVAC system and, by extension, the comfort in your home.
CABS Heating and Air Conditioning is Sacramento’s most trusted HVAC company, and we’d be excited to earn your trust and help keep your furnace and entire HVAC system running smoothly for years to come. Give us a call today!
ADDITIONAL FURNACE RESOURCES:
