Gas Furnace Not Blowing Hot Air [7 Easy Solutions]

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Is your gas furnace not blowing hot air? The last the thing you want to do is turn to your heater and discover that your furnace is not blowing hot air on one of those freezing days in winter. It is already winter and if you are like most people, you are probably turning up your furnace more than fewer times before. That’s why it can be frustrating when you have a furnace that is not blowing hot air. 

gas furnace not blowing air

There are several issues that could make your furnace stop working properly. But you will be surprised to learn that the issues that make your heater stop heating your house are ‘easy’ fixes that you can quickly put your hands on and get your heater back on.  

To better understand what can, stop your heater from running properly, it’s important to know how a gas furnace works. So, let’s briefly look at how this type of furnace works. 


How Does a Gas Furnace Work?

A gas furnace uses natural gas or propane to bring about heating into your home. We won’t go into details here but if you want to learn more about the process, read here (From another website.) During the heating cycle, this is what goes on inside your furnace. 

  1. Your furnace’s burner ignites propane or natural and produces heat. 
  1. The heat from the burning gas heats up the heat exchanger, where air from your home passes. 
  1. The air passing though the heat exchange is then heated up. 
  1. The furnace blower pushes the heated air into the ductwork of your home, distributing it into your home. 
  1. As the warmer air starts fills the rooms of your home, colder and denser air is drawn into the furnace through the return ducts, and the cycle continues and break when the desired temperature is reached. 

Now that we have a basic understanding of what goes on inside your gas furnace, read on to learn more about why it could not be blowing hot air and as we always do, we have provided you with possible solutions to get your furnace back to blowing the warm air you need. 

Reasons For Your Gas Furnace Not Blowing Hot Air 

1)Thermostat Not Set Correctly 

When you notice that your furnace is not blowing hot air, the first thing you want to do when you start troubleshooting is to check if your thermostat is correctly set.  

This sounds ‘no brainer’ but you’d be surprised to know how many times this solves the problem. Make sure the fan is not set to ‘ON’. When it is set to that, your furnace fan continues blowing air even when the furnace is not in the heating cycle.  So, during the down cycle, furnace fan will not blow hot but cold air. 

Solution: The best thing to do when your fan is set to ‘ON’ is to put it to ‘heating’ or ‘auto’. When it is set to auto, it will automatically coordinate with your furnace, when it is in the heating cycle it will blow and when it is in the down cycle, it will not blow air. 


2)Somebody Else Adjusted Your Thermostat. 

Make sure to check that the thermostat is set correctly. When your furnace is blowing cold air it’s a good idea to counter check your thermostat. Somebody else might have adjusted the thermostat either accidentally or intentionally. 

People have different views about temperature comfort and so other people’s comfort temperature can differ from yours. 

Solution: If you notice that your thermostat was adjusted, resetting it to your desired temperature should bring your heat back. 


3)Weak or Dying Thermostat Batteries

 Does your thermostat rely on the central power system? If so, ignore this step and jump on to the next step. But if not, then check your batteries. Remember, batteries don’t have to be totally dead in order to cause your thermostat not to work properly. 

Batteries last a long time before you have to replace them but this could also mean your thermostat is old.  

Programmable thermostats can also affect how your furnace works if they are not properly programmed. A faulty thermostat could also be the reason your furnace is not turning on. 

Solution: Replacing the batteries can have the problem is sorted out. And if your heater gets back on after replacing the batteries, then congrats! You have just fixed your heater without calling in an HVAC professional. 


4)Furnace Air Filters

When you have checked possible thermostat issues and everything seems to be in order, the next thing you want to do it check the condition of your furnace air filters. Clean air filters are critical in the operation of your furnace.  

Dirty air filters will restrict the amount of air flow that’s gets into your gas furnace. This causes the furnace burner to overheat and eventually shut off.  

For some furnaces, there is a built-in auto-shut off system that automatically shuts off your heating system when the air filters get dirty or clogged. 

Before you check the status of your filters remember to turn off your heater. It’s not hard to see if your filters are dirt, if you can’t see white, it’s a sign your air filters need replacement. Disposable air filters are made to be replaced every 1-3 months. 

If you are unsure about what to do, it’s smart to call in a HVAC professional. 

6)Gas Heater Not Blowing Hot Air: Leaking Air Ducts

Air ducts are responsible for carrying hot air from your furnace for distribution throughout your home. They are usually installed outside the heating area of your home. Over time, air ducts can become damaged and could have holes on them. Not only that, some small animals in the attic can bite them and cause them to leak. 

Warm air that is blown from your furnace escapes through the leaks and cannot make it through into your home.  This could just be another reason for your gas heater not blowing hot air. 

Solution: If there are leaks in the ductwork and you think it is something that you can fix yourself, use tape or new pieces to seal them off. If you think you can’t do it, call a professional to come and give a hand. 

6)Gas Valve Problems 

If the gas valve for your furnace hasn’t been cleaned or checked in a long time, dirty and debris can accumulate on it. The valve could shut down and could be the reason for the hot air not blowing out of your furnace. 

Solution:  If you haven’t had your system checked in a while, it’s high time you did. Regular maintenance will also prevent the dirt and debris from collecting on the valve. 

7)Gas Furnace Not Blowing Air: Blocked Registers 

When your furnace is not blowing air, sometimes the problem is not the furnace itself at all, but blocked registers.  Blocked registers could also cause the same issues as clogged air filters do. Blocked registers or vents means that you are not receiving that warm air that you should, and the system is not getting enough air to warm. 

Registers can easily be closed by accident. 

Solution:  You can quickly tell the issue has to do with vents or registers if you notice that just one room is colder than the others. Try opening or unblocking vents and registers if there are any. 

Final Thought


In wintertime all you want is a furnace that is doing its job to keep you and your loved ones warm. However, sometimes gas furnaces do break down. If the problem is your gas furnace not blowing hot air, use the steps given here in your troubleshooting process.  

To avoid unnecessary break downs of your furnace, make sure proper maintenance is done regularly. If you hear strange noises or notice any unusual odour from your heating system, do not ignore. The small issues, if left unchecked can cause unexpected and costly repairs.  It is recommended to have maintenance tune up twice a year.  


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