Furnaces are pretty popular in homes today, in fact, many have even begun to factor it into design when constructing a new house. Due to their nature of the operation, as well as extra installations needed, furnaces are able to produce and distribute heat for keeping the house warm, while its venting duct (if any) is multipurpose in nature, suitable for both dehumidifying and air conditioning purposes. However, running a furnace comes with the risk of carbon monoxide exposure due to its generating heat through combustion. This is a very dangerous gas to be inhaled, making how to fix carbon monoxide leak in furnace guide a must-know procedures for all users.

Also Read: What appliances gives off Carbon monoxide

Carbon monoxide is a colorless and odorless gas, which results from an incomplete combustion process. This incomplete nature could be caused by either a lack of proper aeration, poor combustible material, or heat source. When it occurs, heat is released alongside CO, and if not properly vented, would lead to poisoning air in the atmosphere.

What causes the furnace to leak carbon monoxide

A furnace leaking carbon monoxide to the atmosphere is as a result of cracks in either its flue supply pipes or heat exchanger. These cracks can develop for a lot of reasons, and when they do, it could cause carbon monoxide to leak into your home’s air, which presents a very serious health hazard, including eventual death.


Another cause of carbon monoxide leaking into the home is a result of blocked pathways by clogged filters, leading to the accumulation of CO invent ways, eventually finding their way into the air. There is also a chance that this thing happens if your furnace was not installed correctly.


For example, the blower motor or ductwork was improperly designed, leading to problems while venting, and ending up with CO finding its way into your atmosphere. This is why it is important to always hire professionals instead of cheap labor.

How to tell if your furnace is leaking carbon monoxide

This is a very tricky act to pull off because it can be both dangerous, doing a great deal of damage to the body before anyone even notices. As a result of this, the best and safest way to tell of a furnace is leaking carbon monoxide is by installing carbon monoxide detectors in every level of the home.

Since carbon monoxide detectors are electronics and don’t exactly give a week notice or two before damaging, it is important you also be on the lookout for signs of CO poisoning. According to the Environmental Protection Agency, when on is exposed to low CO levels, it is characterized by fatigue or chest pain, and at higher levels impaired vision and coordination, dizziness and nausea, confusion and headaches. Further exposure could be fatal. The following signs could also mean a leaky furnace

  • Heavy condensation appearing on windows where the furnace is installed
  • Sooty stains are appearing around the furnace. It could also be a form of a brownish-yellow color
  • The physical appearance of soot, smoke, fumes or back daft in the house from the furnace
  • A burning like/ overheating smell. Sometimes this is also accompanied by the smell of unusual exhaust gases that accompanies the odorless carbon monoxide.
  • For furnace with visible indication, a yellow burner flame instead of the clear blue one could mean incomplete combustion, hence CO present. This, however, does not apply to all furnaces.

How to fix a carbon monoxide leak – step by step furnace repair

The first way to dealing with carbon monoxide leaks in your home is to ensure not even the slightest bit of it goes undetected. You can only correct after diagnosing a fault.

Use the following DIY procedures on how to fix carbon monoxide leak in furnace

  • Install a CO detector to keep tabs on contamination levels before and after dealing with the leakage.
  • Turn off the furnace.
  • Leakages resulting from cracks would be either from the flue gas line, the heat exchanger, or the vent system. Carefully inspect all of these systems with adequate illumination, for openings like cracks, rusts, holes, gasket leaks visually, and take note.
  • Due to the obvious limitations of the eyes, there is only so much they can capture, which is why you should never rely on it alone to confirm a leakage. There are several test kits that can be used, but for the sake of a DYI, we recommend carrying out a simple dye test. This involves using a penetrating dye like Magna flux, spraying it over suspected areas, and then investigating the interior for leakages.
  • Replace every faulty part with a new one properly.
  • If you also have a vent installed, check for clogging of filters, which could cause CO to get trapped within the duct. Wash and dry all filters.
  • Start your furnace again, and observe if there are any more CO deposits through the detector. If present still, invites a professional to come to carry out overall maintenance, and a more thorough leakage inspection.

Can a furnace leak carbon monoxide when turned off?

There is a good chance that carbon monoxide still leaks from a furnace, although it is off. In the real sense, the system wouldn’t be producing CO anymore when the furnace is off; however, it could have produced some who still lingers in the heat exchanger or vent duct. If this gas finds its way into the home for any reason, it can lead to poisoning though the device is off. There is a high chance of this happening because CO lingers around for a pretty long while.

Turning off the device doesn’t guarantee any leak situation alone, but rather alongside proper venting after it goes off. When multi-purposed, the vent could also take in CO from other sources in the home, still retaining its risk of exposing the atmosphere to this dangerous gas.

Dangers of a carbon monoxide leak

The symptoms of getting exposed to mild carbon monoxide poisoning are pretty similar to that of a cold or flu and may include more than one of; headache, dizziness, nausea, fatigue.

At a higher level of exposure, these symptoms graduates to disorientation, loss of coordination, vomiting, and even fainting. After continual exposure despite these symptoms, the resulting outcome could be fatal. Keep in mind that these symptoms vary depending on the volume of CO exposed to per time, as a higher amount would always yield faster effect.

Final Thoughts on Fixing CO leak in a Furnace

Carbon monoxide is no friend to the body of a man and should be avoided by all costs. This is why it is also necessary to install safety measures along with any installations that present a risk of CO exposure, like a furnace. Other ways to Heat a House without a furnace could also be considered.

In the event of noticing CO poisoning symptoms, leave the area immediately to a location with fresh air as fast as possible, preferably not a confined space, and breathe properly. Thereafter, place an emergency call to 911.

Relevant Reviews: