Most people don’t expect their water heater to release harmful gases, but the reality is otherwise. This guide breaks down how to tell if your water heater leaks carbon monoxide and what that really means for your home.
Can a Hot Water Heater Release Carbon Monoxide?
You may already know that your water heaters burn natural gas to heat water, and that creates carbon monoxide in the exhaust. That gas moves up through a flue in the center of the heater and exits through a metal vent pipe at the top. A water heater can leak carbon monoxide when the vent is not installed in the right way. That pipe rests on a small chimney-shaped funnel, and the weight of the pipe is supposed to hold it in place.
If that pipe is not sitting right, if it’s pulled off or tilted to the side, carbon monoxide starts to leak straight into the house. It needs to be lined up with the collar at the top of the vent, which directs the fumes outside. If the pipe sits loose or doesn’t fully cover the collar, the gas escapes into the room instead of going out through the roof.
The preferable indoor areas to install your water heater are a garage, basement, attic, or a dedicated utility room. In some cases, the water heater gets clogged for many reasons. There could be a bird’s nest, or a nest that dropped in from above. There’s also a possibility that an animal has found a way inside your home where you installed the water heater, removed the cap or collar from the top of the vent, dropped into it, and then later died.
So, if anything blocks the inside of that pipe, the carbon monoxide can’t escape upward, so it releases into the home instead.
How to Know If a Water Heater Is Leaking Carbon Monoxide?
1. Buildup of Condensation on Windows
If your water heater leaks carbon monoxide, one early sign can be heavy condensation on the inside of your windows where your appliance sits. This happens because carbon monoxide is part of the combustion gas, and when that gas leaks into the room, it raises the indoor humidity. That extra moisture does not exit through the vent. It stays in the room and starts collecting on cold surfaces like glass.
You may notice this especially around the same time the water heater runs to make water hot. It’s not a small amount either, and looks more like someone boiled a pot of water nearby. This type of condensation, even if the weather outside is clear and there’s no steam indoors, points to poor ventilation.
2. Yellow or Brown Soot-Like Stains Around Exhaust Vent
You may see yellow or brown stains near the exhaust vent. These stains look like soot or powder, and they often collect around the draft hood or on the wall just above the heater.
These stains could be streaks, smudges, or patches near the top collar or around the vent pipe. They don’t wipe off easily and tend to build up over time. Even if the water still heats like usual, those stains show that the venting is not working correctly, and the exhaust gases are escaping with carbon monoxide in them.
3. Stale or Heavy Indoor Air
If the vent does not work correctly, the gas that should leave through the pipe stays in the room. That turns the air stale, heavy, and uncomfortable, especially if the room does not have much airflow.
This is a clear sign of trapped exhaust gas that no longer exits through the vent. You do not notice a strong smell at the start, but after a few minutes in that space, the discomfort sets in. You may get a headache, or your throat dries out for no clear reason. Then you open a window or the door for a few minutes, the room clears up, and everything’s normal again.
In case the same thing happens every time the water heater runs, then it is not just the room. It is what the heater pushes out into it.
4. Flu-Like Symptoms Without a Known Cause
Carbon monoxide from a leaking water heater, which is making its way into other rooms of your home, can affect your health directly. You might experience body aches, fatigue, nausea, or a slight headache. These symptoms are mild at first, so most people confuse them with the flu. The major difference is that the symptoms show up at home and fade when you spend time outdoors.
It is not a coincidence that these symptoms come back when you step into the house again. It shows that something in the air is not right. Carbon monoxide affects your body slowly, and it does not give off any warning by smell or color.
5. Pets Get Sick or Weak for No Clear Reason
Carbon monoxide can affect pets faster than it affects you. If a gas water heater starts to leak this gas, your cat or dog becomes the first to react. An active cat suddenly lies down in the same corner. A dog that eats well every day may avoid its food or act tired for no reason.
Then you notice something strange. Once your pet is outdoors, its behavior improves. It becomes alert again and goes back to normal. Like you, that shift is not a coincidence, and now you know the reason for it.
6. Burning or Sharp Smell in the Room
Carbon monoxide itself has no smell, but the exhaust from a water heater can include other gases that leave a burning or sharp scent. That scent shows up near the vent or around the top of the heater, often right after it finishes heating the water.
You might catch a strong hit of it as you step in where you placed the water heater and the mild one in other parts of your home. This problem is again wth the venting pipe that is blocked or not installed correctly.
7. Yellow or Orange Pilot Light or Constant Blowouts
The pilot light in a gas water heater should be blue. If you notice it turning to yellow or orange, it means the gas-to-air ratio is incorrect and a lot of air is getting into it, which means the water is not working efficiently, and this leads to carbon monoxide production. This points to an issue with the pilot tube or the pilot valve, so you fix it as soon as possible.
8. Rust on the Vent Pipe
Another telltale symptom of the water heater leaking carbon monoxide is the rust on the vent pipe. The exhaust gases coming out of the appliance are water vapor, and when those gases get stuck in the pipe or leak out, they cause rust to form. You might notice small spots at first, and later full rings of corrosion near the joints or seams.
Rust near the draft hood or collar also means the pipe may be leaking gas at that point.
What to Do If a Water Heater Is Leaking Carbon Monoxide?
If you can do it yourself, take the water heater top vent apart, look inside, and get rid of whatever is clogging it. In case this is not the source of the problem, call California Coast Plumbers to diagnose the issues with the vent pipe and look at other issues going on with your water heater.
Another good practice is to install the gas water heater outside your home, which not only saves space but also means you won’t need ventilation and deal with the carbon monoxide buildup inside.