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Furnace blowing cold air

Why Is My Furnace Blowing Cold Air?

Normally, we rely on our furnace to keep us warm. When your furnace is not blowing hot air, you know right away that you’ve got a problem. 

If your furnace is blowing cold air, it’s easy to panic. The good news is that there are several reasons why your furnace might not be co-operating, and we can help you figure out which of several reasons could be the culprit for your furnace not working properly

We’ll walk you through some furnace basics, talk to you about the key components, walk you through some troubleshooting basics for a furnace blowing cold air, and help you to understand when you should think about contacting a professional. 

If you’ve got cold air blowing out of your vents when the heat is on, check out this guide, and follow the steps to diagnose, and potentially fix the problem. 

If you’re looking for some winter furnace maintenance, check out our post on the subject. 

Furnace Basics

Furnaces are one of the key components of your heating system. In a perfect world, your furnace should produce the heat that keeps your home at a comfortable temperature. 

Your furnace pulls in air, heats it, then pushes it throughout your home to increase the ambient temperature. This is how your heating system heats the house. There are a few components that could lead to problems with your heating system. 

It’s worth mentioning that electric furnaces are slightly different, and could feature a different set of issues. 

The first one we’re going to talk about is your fan. 

Fan Settings

The first thing to understand about furnaces has to do with the fan. Chances are, your furnace has a large fan that pushes air through your heating ducts. This fan is important because the heated air needs to get throughout your home, or you wouldn’t notice any difference when the furnace was operating. 

The operations of this fan are often linked to times when your furnace is running. After all, if the goal is to push warm air throughout your home, then the fan is the tool to do this correctly. 

One common problem that we see is the fan running when the furnace isn’t. This would continue to push air throughout your home, but that air won’t benefit from the heating quality of the furnace. 

Your furnace control panel or thermostat could help you to find out if this is the problem. If your fan is set to ‘auto’, then it should only operate when the furnace is heating the air. If it’s sent to ‘on’, then it may be pushing air independent of the furnace’s operations. 

Make sure your fan is operating in the manner you want. If your main problem is that your fan is blowing cold air, then try switching it to the ‘auto’ setting. If your fan only runs when your furnace is heating the air, then you’re much less likely to experience your furnace blowing cold air. 

If this doesn’t fix your problem, and your furnace is still not blowing hot air, you can move on to some of the other potential culprits. 

Pilot Light

Your pilot light is another important component of your furnace. Essentially, your pilot light is a small flame that exists to ignite the gas that your furnace releases, to start the combustion process and heat the air. 

The pilot light does represent one type of danger that can occur. If the pilot light goes out, the gas that your furnace releases won’t ignite, it will simply collect in the furnace area. Then, any spark or source of flame could cause all of this built-up gas to explode. 

For this reason, pilot lights should be on your mind when you’re thinking about potential problems with your furnace. They can cause your furnace to misbehave and blow cold air, but they can also create a very dangerous situation. 

 Generally, you can check on your pilot light by removing the furnace cover panel. The pilot light will likely be visible. If you see a flame, that’s good news. It should be fairly blue with a small yellow section. 

Relighting your pilot light is an important skill to have, but not necessarily a beginner’s task. The specifics of how to relight your pilot light will depend on the make and model of your furnace. Reading your user guide on how to relight your pilot light can give you the knowledge you need to safely perform the task. 

In general, your pilot light is relit by shutting the gas off, waiting for any residual gas to dissipate, lighting a match, and holding it near the pilot light while setting your pilot light gas setting to ‘reset’. This is only general advice, and not a substitute for the specifics of your furnace, or expert knowledge of furnace maintenance. 


Another potential problem could be relating to your furnace filter. Your filter could be clogged with dirty air particles and may be suffocating your furnace. If this is the case, your furnace might be struggling to get the proper intake of air. For safety reasons, your furnace might be shutting itself off, to prevent a disaster from happening due to poor airflow. 

You should check your furnace filters often, and follow the suggested replacement schedule outlined in your owner’s manual. 

Condensate Problems

If you have a high-efficiency furnace, you might have to deal with condensate. Condensate is the byproduct of the heating process in a high-efficiency furnace. In essence, it’s water. It should be drained appropriately to make sure that your furnace continues to operate at maximum efficiency. 

If you have a high-efficiency furnace, and you think condensate may be leaking or pooling, reaching out to an expert might be the best choice, as high-efficiency furnaces are more complex than other styles. 

When to Call an Expert

If you’ve looked through our guide and you still don’t know why your furnace is blowing cold air, it might be time to reach out to an expert. 

An HVAC expert can correctly identify your furnace problems. They can safely establish what’s wrong, and help you fix your furnace. Experts can remove the stress of trying to self-diagnose your furnace problems by bringing expert knowledge and experience. 

If you’re looking for an HVAC expert in Phoenix that is sure to diagnose and fix your furnace, head to American Home Water and Air’s furnace page to get the expert help you need. 

Frequently Asked Questions

Why is My Furnace Blowing Cold Air when the Heat is On?

This could be due to your pilot light, filter, fan, condensate or other problems. Some diagnosis is required to find and address the root cause. Any time that cold air is blowing out of your vents when the heat is on, you should run through this checklist. 

How Can I Tell if My Pilot Light is Out?

Try to get a visual look at the pilot light. Removing the exterior furnace panel should reveal the thermocouple and pilot light. If you don’t see flame, that’s a sign that your pilot light isn’t operating as intended. 

What to do if I Smell Gas at My Furnace?

This is a major safety concern. If safe to do so, you should shut off the source of the gas to your furnace, evacuate your home, and call the fire department. The buildup of flammable gas can have a catastrophic effect if it reaches a source of ignition. 

We hope we’ve helped you understand your furnace issue, and that your home gets back to the comfortable warmth that your furnace can provide. 

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