Why Furnace Is Not Blowing Hot Air?

There are few things more frustrating than dealing with a furnace that won’t blow out hot air. You’ve tried everything that you can think of, and still, you can’t figure out the problem. 

There are several reasons why your furnace is not blowing hot air, but some of them are: Dirty Air Filter, Issue With Furnace Ignition System and Issue with House Temp Thermostat.

This article will not only help you troubleshoot common causes of the malfunction, but it will help you recognize when a professional’s help is necessary.

The Furnace Air Filter is Dirty

When your gas furnace’s air filter is covered in gunk, there’s no way that it can blow out warm air, and here’s why.

When a dirty filter restricts airflow within the furnace, the furnace begins to overheat.

And as a protective measure, the furnace blows out cold air to cool itself down. This functionality is seen in just about all furnaces. 

This is a common reason why furnaces blow out cold air. 

The appropriate course of action to take when the furnace filter is dirty is to replace the current furnace filter with a new one.

This can be done at home if you’re up for a bit of labor. 

If you have an oil filter, read on- oil furnace issues will be discussed further down in the article. 

Replace Your Furnace Filter

Below are some steps for replacing a furnace filter. 

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  • Access your current filter and take it out. Furnace filters can be easily found inside the furnace or in the air return vent. 
  • Make a note of the size and type of filter you’ve just removed. Grab a piece of paper and pen and write that down. You’ll need that when you go to purchase a replacement filter. 
  • Purchase and replace the filter. After purchasing a new filter, make sure that you are putting it in the right way. A quick way to find out whether you’re putting the filter in the right way is to point the edge of the filter in the same direction as the blower motor

Note: If you put the filter in the wrong way, the furnace won’t be able to blow out air as strongly as it would normally be able to. 

The Furnace Ignition System is Faulty

A furnace’s ignition system is extremely important to its functionality. When the ignition system is in flux, the furnace will not be able to blow out cold air. 

There are two components of a furnace ignition system that you should know about: 

  • The pilot light
  • The ignition

If your furnace doesn’t blow out hot air, it could be that either the pilot light is out or that some part of the ignition system is not working properly.

Both of these issues require a bit of finesse to troubleshoot and repair. If you have tried everything else, it is wise to reach out to an HVAC technician for assistance. 

Thermostat Is Not Signaling the Furnace to Heat

If you’re someone who isn’t experienced in working with thermostats, it’s important to know that your thermostat is in sync with your furnace.

If your thermostat is not signaling your furnace to turn on, the furnace will not blow out hot air.  

As time goes on, the average thermostat is getting more intricate and complicated.

On the other hand, if your thermostat is old, you may find that there is a learning curve to learning how to operate it properly. 

The Temperature is Wrong

Here are a couple of things that you can do to make sure that your thermostat is set to the right temperature: 

  • Check the manufacturer’s instructions. If you don’t know exactly how to set your thermostat to the right temperature, you should first look at the manufacturer’s instructions. Alternatively, you can search for the instructions on the web or give the thermostat manufacturer a call. 
  • Ensure that your thermostat is on “Heat.” Some thermostats won’t prompt the furnace to blow out hot air unless it is set on the “Heat” function, whether you’ve set the desired temperature to 50 degrees or 80 degrees. 

After you’ve done the above, if the furnace is still not working properly, something else could be to blame. 

The Thermostat is Dead

One common cause of a faulty furnace is a dead thermostat. Thermostats commonly malfunction due to technical problems that only an HVAC technician would understand.

However, there are times when the wires in your thermostat need to be resecured, or it needs a new battery.

These are things that you can check yourself, in most cases. 

If you have an electric thermostat, you may be able to easily open up your thermostat, purchase a new battery that matches the one you removed, and replace it with a new battery

But in some cases, you may need to enlist the help of a technician to replace the battery. Also, removing the face of your thermostat will reveal its wires-make sure that they are secure. 

The Thermostat is Dirty

For mechanical thermostats, over time, the inside can become dirty and cause it to malfunction. To get rid of dust and debris, open the front of the thermostat and blow any debris away. 

The Thermostat is Not Compatible

If your thermostat is not compatible with your thermostat, your furnace will not function in tandem with it.

The chances of this being the issue are slim unless you’ve recently installed your own thermostat without the help of a professional. 

If you aren’t sure whether your thermostat is compatible with your furnace, a professional can confirm this for you. 

This is not likely to be the issue if your furnace was working properly before and has only recently started blowing cold air.

Your Furnace Is Out of Oil or the Filter is Clogged

This section is for households with an oil furnace.

For people who have a furnace that operates on oil, it may be worth it to check the oil tank and make sure it’s not empty.

If it is empty, the internal burners will not light. This can cause the furnace to blow out cold air. 

Over the winter, an oil furnace can guzzle 3 gallons per day for the average household.

It also varies with the user’s habit and preference. If you have been using the heat more often than usual, you may have run out of oil without noticing. 

The oil filter can be another reason why your furnace won’t blow out hot air.

If the filter is clogged, this can cause issues with the ignition system within the furnace, and a replacement filter would need to be fitted.

Note: The process of replacing an oil filter is much more involved than replacing an air filter (for those who have a gas furnace).

However, if you have prior knowledge of oil filters, you could replace the filter yourself. But most people call a professional for help with an issue like this. 

The Gas Line Shutoff Valve is Engaged

If someone has been fiddling with your furnace lately, they could have switched off your gas valve and forgotten to put it back in the “On” position.

If this is the case, there is no way for your furnace to generate heat. 

To troubleshoot this issue, you’ll need to check the valve’s position. If you don’t know where the gas line shutoff valve is, you can simply follow the gas line from the meter to the furnace

Once you’ve located the valve, observe its position. If it turned horizontally, it is in the “off” position. To turn it back on, turn it to the vertical position. This should solve the problem in no time. 

Your Gas is Shut Off at the Source

Have you paid your heating bill? If your furnace isn’t blowing hot air, it could be that your heat is turned off. If this is the issue, once the heat is turned back on, your furnace should be in working order again. 

Duct Problems are the Cause

Over time, air duct problems can arise, showing themselves in the form of holes and leaks.

These leaks and holes allow room temperature air to directly invade your ducts. This issue is more common in older furnaces than those that have been recently installed. 

This is not a problem that can be troubleshot and fixed by a non-professional. It’s best to contact a reputable HVAC company to fix an air duct problem.

To save money, make sure that you check for easily fixed issues before calling in a professional. 

The Furnace Needs a Restart

If you have a new, high-tech furnace that has electronic controls, the issue could lie within that system.

This is not a likely issue if you have a standard furnace, though. 

Resetting your furnace’s computer system can be the jolt that your furnace needs to blow hot air again.

For many of the newer furnace models, a restart is as simple as pushing the power button on your furnace’s control panel, waiting several minutes, and then powering it on again. 

If this does not work, explore other options. 

Final Thoughts

So many things can go wrong with a furnace (or the thermostat that controls it) but taking a bit of time and troubleshooting common issues can help you fix the issue yourself.

Yet, many furnace issues will require the expertise of a professional. We hope that this guide will help you successfully pinpoint your furnace issue. 

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