Why Is My Furnace Not Blowing Out Hot Air?

10 Reasons Your Furnace Is Not Blowing Hot Air

1. Problems with the Thermostat

Sometimes it’s not your furnace’s fault that it is sending an Arctic chill instead of the heat you want. It’s possible that the problem is caused by the thermostat. Focus your initial troubleshooting efforts here, since you have the best chance of resolving the issue without involving a professional. Thermostat problems come in a variety of flavors, each with its own set of solutions. These range from the obvious face-palm to the slightly more nuanced and technical. Here they are, in that order:

The fan is turned on. 

If your fan is set to continuously blast, it will blow chilly air at some time. The reasoning is simple: furnaces do not continuously pump out hot air. When the thermostat indicates that warm air is required, it is sent through your ducts. When the air temperature hits the temperature you’ve set — let’s say 70 degrees — the furnace can turn off until the temperature goes below 70.

  • However, if your fan is set to “on” all the time, it will blow frigid air during the furnace’s downtime. As a result, set your fan to “auto” to work in tandem with the furnace, and you’ll only get hot air instead of chilly.

The thermostat is being adjusted by someone else. 

If you’ve ever worked in an office where someone has turned the air conditioning up to 11 to the detriment of others, you’ll understand what I’m talking about. We all have various tolerances for cold, and we all have different notions about how warm the house should be.

  • Thermostat battles can easily lead to someone hitting the fan “on” setting by accident. And, as you’ve just learned, this can cause your ducts to spew cold air. It’s time to have a family discussion on compromise.

The battery is nearly depleted. 

A depleted battery, in addition to the other foolish mistakes people make with their thermostats, is readily fixed. Some thermostats are powered by the home’s central power supply, while others are powered by a self-contained battery unit. This is the type that will occasionally run low and, as a result, will need to be checked from time to time. Even a low-battery condition that isn’t nearly dead can cause issues. It does not have to be completely dead in order to cause your thermostat to malfunction.

  • However, because thermostat batteries endure a long time, this is more likely to be an issue if your thermostat is older. In any case, check the batteries before hiring a professional HVAC technician; you might spare yourself some humiliation. 
  • We’ll be dealing with a slightly more complicated set of furnace difficulties from here on out. They’re not usually caused by user error, therefore they’re more likely to require outside assistance than the problems you’ve seen thus far.

During your DIY thermostat installation, you overlooked something.

 When it comes to installing a new thermostat, some people prefer to hire a professional, while others prefer to do it themselves. This problem is actually extremely common, given the tremendous surge in popularity of programmable thermostats over the last several years.

  •  We’ve seen several customers purchase a fantastic new thermostat only to discover that it is incompatible with their home’s existing heating system. If you think that’s what happened in your situation, the next step is to contact an HVAC specialist who can tell you what’s going on. Even if you’ve made a complete mess of things with a jumbled-together system of DIY parts, a pro will be able to sort it all out and figure out what’s causing your thermostat problems.

2. Filtering Problems

Another user error could be causing your cold air problems. After checking the batteries and checking for thermostat tampering, change the filter in your heating system. Unclean and outdated filters can obstruct airflow to your HVAC system. As a result, your furnace’s ability to create and distribute warm air may be compromised. One type of furnace even has an automatic cutoff when the filter is clogged to prevent overheating. The furnace will then blow cold air. Filters are cheap and easy to change. If yours is muddy, it’s time to replace it. Then restart your furnace. Wait a few moments for the ducts to warm up. If so, congrats for thinking out a solution without hiring a pro. Other options exist if changing the filter and restarting the computer doesn’t work.

3. Problems with the High-Low Switch

If left ignored, a blocked filter might create malfunctions in your HVAC system. Some overheating is to be expected, but not forever. Regularly overheating your high limit switch can cause failure. It’s enough to know that you don’t want the high limit switch to fail. A dead or dying plant’s “brain” will think the furnace is hot. It will turn on the fan to cool things down. But all you see is the furnace blower running and spewing cold air, with no apparent reason. Not understanding your high limit switch is dead will leave you puzzled (or even that such a part exists). The switch may also be challenging to detect, necessitating HVAC expert assistance.

4. Problems with the Condensate Line

Your HVAC system’s condensate also needs frequent maintenance. In hot conditions, the condensing unit drips water into a drip pan. This water is extracted through plumbing and released outside your residence. Those pipes tend to get blocked with dirt and filth if not cleaned regularly. Naturally, the more you use your smartphone, the slimier the pipes become. If they become clogged, your system will shut down. Filth builds up near the end of the summer, just in time for your furnace to start blowing cold air. The moral of the story is to keep those condensate lines clean. HVAC companies supply specialized tools for cleaning sticky condensate lines.

5. Source of the Issues

Does everything “go” at the fuel source? This is a simple question that far too many homeowners overlook. There’s one for every type of furnace out there, and it’s dead simple to fix:

  • Furnaces that run on oil. Is there any gasoline left in the tank?
  • Furnaces powered by electricity. Is the furnace turned on at the circuit breaker? Is the furnace on by itself?
  • Furnaces that run on gas. Is the gas supply valve in the open position? If it isn’t, there’s a good risk the gasoline won’t make it to the burners.

6. Adding Fresh Air to the Mix

The ducts that distribute warm air throughout your home might deteriorate over time. They’re frequently placed outside of our home’s heated room, exposing them to harsh temperature variations all year. These variations might generate weak places in your ducting, which can potentially lead to leaks. There are a variety of dangers that might lead to leaking ducts. Consider the following scenario:

  • Leaks can also happen in ducts that have been disconnected.
  • Previous duct tape fixes may come undone if the tape peels away.
  • When ductwork is not correctly screwed together, it might fracture.

When your ducts leak, the chilly air that surrounds them can get in (and hot air will get out). The addition of outside air decreases the temperature of the air that has just exited your furnace. It is the colder air that is blown into your living spaces.

7. Issues with Pilot Lights

Has your gas company had to do maintenance recently, or has there been any emergency line work? If that’s the case, your pilot light may have gone out as a result of them. A pilot light, similar to the one found on a gas stove, is included in a gas-powered furnace. These, too, can be blown out. The pilot light on older furnaces is more prone to go out. Even a brisk walk too close to the furnace can create enough air movement to cause this.

8. Problems with Gas Valve

Again, maintenance issues: if your gas furnace hasn’t been cleaned in a long time, a defective valve could be the cause of the frigid air blowing out of your furnace. The valve can become clogged with dirt and debris, forcing it to shut down. It’s also possible that the valve is simply worn out. Another incentive to have your system checked on a regular basis.

9. Problems with the Burner

The furnace’s burner is yet another HVAC component susceptible to filth and grime-related issues. There won’t be any fuel getting through if it’s plugged. However, your fan may continue to run, resulting in chilly air entering your ducting. Cleaning your burner is the best solution. Homeowners who are motivated and handy can learn how to do it manually on their own. However, the best scenario is to get a professional to come in and clean it thoroughly.

Issues with Flame Sensors

Your furnace will also blow chilly air if the flame sensor is old or unclean. Your burner will repeatedly shut off if the sensor isn’t operating properly because it’s covered in filth. The fan, on the other hand, may continue to rock, causing the chilly air to blast. Maintenance is required on a regular basis.

One Last Thought on Your Heating System

When you’re expecting warmth from your heating system, a multitude of flaws can cause a terrible blast of chilly air. Some conditions can be self-diagnosed and treated. Others will necessitate the assistance of an HVAC professional. There’s one other issue that hasn’t been addressed yet: you could just need a new furnace or emergency furnace repair . If that’s the case, you’ll want to consult an expert before taking action on the final answer. They’ll assist you in determining the best type and size of heater for your home. But, in the interim, try some of the adjustments we’ve discussed here, starting with the easy fixes you can do yourself. 

If you think you might need some help on furnace repair tips contact us at (219) 306-2348 for more info on furnace repair services and more!