When it's cold outside, you need your furnace to work.
So if the furnace is not blowing hot air, you're probably getting worried! What will you do if the furnace won't heat the house?
Before you bust out the extra layer of sweaters and sweatpants, take heed of the guidance in this article. In many cases, it's easy to get a furnace working properly again-without calling an HVAC contractor!
Let's take a look at the most common reasons a furnace might not be blowing hot air. For each reason, we specify whether this is something the homeowner can address or if it's best left to a professional.
Reason #1: Improper thermostat setting
Who can fix this? Homeowner
This is actually super common. At some point, somebody might have moved the little switch on the thermostat from "heat" to "off" but left the blower fan running.
When this happens, you will feel air coming out of the vents but the air won't be hot.
Simply flip the switch back to "heat" and voila! Your furnace will run again! Just set the desired temperature on your thermostat and get cozy.
Reason #2: Dirty air filter
Who can fix this? Homeowner
Your furnace can't heat properly if there isn't enough air moving through it. When your air filter gets really dirty, it can block air from entering the furnace.
The unit will continue to run, but it won't heat very well. It might seem like the furnace isn't blowing hot air at all.
The solution is simple: Replace the air filter. Or, if it's a washable filter, wash it and put it back in place.
Basically, it's important to follow the air filter manufacturer's instructions with regard to washing or replacing the filter. Most disposable air filters are good for 90 days before they need to be replaced.
Reason #3: Air vents are closed
Who can fix this? Homeowner
So your furnace is running but your house isn't getting warm. What gives?
Check to see if anyone closed your air vents recently. Sometimes people do this when they're doing work around the house, kicking up lots of dust (drywall work, anyone?), and want to keep dust out of the air ducts.
One or two closed vents might not be a big deal, but several closed air vents can be a problem! Most of the air produced by the furnace will only go to a limited area of the house, leaving other areas cold.
The fix is to open all the air vents so the system can properly distribute air.
Reason #4: Closed gas valve
Who can fix this? Homeowner
Did you close your gas valve after the last heating season?
If you did, your HVAC system might run and the fan might blow air. However, the furnace isn't getting any fuel to burn and generate heat.
Turn the system off, open the gas valve, and then turn it back on to see if it's heating properly.
Reason #5: Failed hot surface igniter
Who can fix this? HVAC contractor
This is one of the most common failure points for modern furnaces. If the hot surface igniter goes bad, the furnace can't produce a flame to start the fuel combustion process. You will feel the blower fan moving air through your ducts, but the air won't be hot.
Luckily, your HVAC contractor can fix this. It's such a common issue that nearly all technicians will have the replacement part on hand.
Honorable mention: The pilot light isn't lit
Before furnaces had hot surface igniters, they had pilot lights. Remember those?
If you've got a really old furnace, you might still have one!
Another reason the furnace might be running without producing hot air is that pilot light isn't lit. You may have to turn the furnace off, manually light the pilot light, and then turn the unit back on.
Reason #6 The furnace is dirty
Who can fix this? HVAC contractor
A dirty furnace won't heat properly-or at all!
If your furnace isn't blowing hot air and you can't figure out why, try to remember the last time you had it serviced.
Has it been a while? Then there's a good chance it's super filthy inside.
During maintenance visits, a good HVAC contractor will clean the flame sensors, burners, blower motor, and other components that can impede proper furnace operation when they get dirty.
Of course, if you have the furnace serviced every year before the heating season, you won't have to worry about the components being dirty-ever.
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Reason #7: Ductwork problems
Who can fix this? HVAC contractor
We see ductwork problems at many of the homes we visit. Unfortunately, these problems tend to get worse over time.
If your furnace isn't blowing hot air, there's a chance that your ducts are:
- Leaking
- Bent or kinked
- Damaged
Duct leaks tend to get worse over time, especially if your installer used low-quality tape that falls off of the ducts. Flexible ducts can also get kinked or bent when contractors do work in your attic or crawlspace.
Also: animals. If, say, a raccoon got into your crawlspace and tore up your ducts, the hot air from your furnace might never make it into the house.
Honorable mention: Improperly sized ducts
If your ducts were too small from the start (a common problem!), your furnace might struggle to move enough air to the areas of your home that need it. This problem won't show up as the furnace suddenly not blowing hot air, which is why we're not listing it as a primary reason.
Still, it's a major problem in homes all throughout our area.
The best way to address ducts that are the wrong size is to perform a Manual D ductwork sizing exercise to determine the right sizes. From there, a contractor can remove the old ducts and install new ones that distribute air properly.
Conclusion: There's always a solution when the furnace isn't blowing not air
Sometimes, it's something you can fix yourself.
Other times, you'll need a professional to diagnose the problem and perform a repair.
Regardless, just because the furnace isn't blowing hot air now doesn't mean it's a lost cause. Use this article as a guide for troubleshooting your furnace. We're confident you'll get it going again-even if you have to call in a contractor!
If you're worried about a misbehaving furnace at your Atlanta-area home, PV Heating, Cooling & Plumbing can help! Call us today at (404) 798-9672 or schedule service online!
