How to Tell If Your Furnace is Leaking Carbon Monoxide?

Think your furnace may be leaking carbon monoxide?

If you are finding signs of soot, a funny smell or the pilot light is yellow and not blue, you may have a carbon monoxide leak.

Below you’ll find out what causes a carbon monoxide leak and how to prevent carbon monoxide leaks in the future.

Let’s get started.

Why Your Furnace Might Leak Carbon Monoxide

Cracked heat exchanger

Heat exchangers do just as the name suggests, they transfer heat from one area to another.

If there is a crack in your heat exchanger, the air will run across the burner which can lead to incomplete combustion and result in carbon monoxide buildup.

Clogged filter

If you have a clogged furnace filter, it can cause an accumulation of carbon monoxide buildup. The carbon monoxide will eventually find its way into your air supply.

Furnace wasn’t installed correctly

Poor installation can cause your furnace to improperly vent which will end up with carbon monoxide buildup in your home.

The best way to diagnose this is by hiring a professional HVAC technician to take a look at your furnace.

Signs Your Furnace is Leaking Carbon Monoxide


If you notice soot stains on or around your furnace, it’s indicative of leaking carbon monoxide. The soot stains can be brown, yellow or black.


If your pilot light is yellow and not blue, then it’s another sign that you’re experiencing carbon monoxide leaks.


You won’t be able to smell carbon monoxide, but the problem your furnace is experiencing may give off an unusual odor.

If you smell something funny, you should call a professional to come and investigate.

Symptoms of Carbon Monoxide Exposure

Overexposure to carbon monoxide can lead to carbon monoxide poisoning. If you feel any of the following, then stop using your furnace immediately and call your local HVAC repair man.

  • Feeling sick
  • Tired and confused
  • Stomach pain
  • Shortness of breath
  • Weakness
  • Nausea/vomiting
  • Chest pain

What to Do If You Suspect a Carbon Monoxide Leak

If you suspect that carbon monoxide is leaking from your furnace, then you should stop using your furnace immediately.

The carbon monoxide can be indicative of a gas leak, which can be dangerous even if you aren’t using your furnace.

It’s best to leave the house and take any pets with you and call your gas company and an HVAC technician to come to diagnose the issue.

It’s better to be safe than sorry, and you don’t want to be inhaling dangerous fumes in the meantime.

If you’re apprehensive about turning on your furnace this winter, you can always schedule an appointment with an HVAC technician to do a yearly check-up to ensure everything is working as it should.

How to Prevent Carbon Monoxide Exposure

If you use gas or a furnace often, then carbon monoxide detectors can be a literal lifesaver.

It’s an inexpensive device that will warn you when the carbon monoxide levels are reaching a dangerous threshold.

First Alert CO600 Plug-In Carbon Monoxide Detector

Key Features:

  • Affordable
  • 7 year warranty
  • 85 decibel alarm

Another great way to prevent carbon monoxide is by having regular checkups on your HVAC system. If you haven’t scheduled yours already, it’s never too late.

Should You Call an HVAC Technician?

Carbon monoxide is an odorless and colorless gas that can make its way through your entire home.

If you suspect that you may be suffering from any symptoms or are finding signs that your furnace is leaking carbon monoxide, then you should call an HVAC technician immediately to come to take a look.

You may also need to install a new furnace, which can take some time.

If you smell gas, then you should leave your home until you’re able to confirm that you don’t have a dangerous gas leak inside your home.

About Roy Cohen

Roy Cohen has a burning passion for heating, cooling, and ventilation. He aims to help you save money on expensive repairs and bring you the best HVAC products. He has years of experience behind him in HVAC repair and garage maintenance.

You can find Roy at his LinkedIn or his email: [email protected]

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