A man standing in front of a furnace with flames coming out of it.

7 Bad Smells That Could Come from Your Furnace and What They Mean

Furnace problems stink. Sometimes literally.

It can be easy to assume a smelly house is a dirty house, but stinky furnaces don’t care how often you clean the rest of your house. You could have the cleanest house in the world, but your furnace might smell like rotten eggs or burning rubber. That’s because there’s probably something wrong! If your home’s heater is putting up a stink this winter, it might be a cry for help.

1) Burning Plastic or Rubber Smells, or a Metallic Smell

If you smell something like burning plastic, rubber, or metal, it’s likely coming from an overheating component in your furnace. Turn your furnace off and call us! If a part of your furnace is overheating, it could turn into a fire in your home. It’s best to have us out to make sure everything looks ok before you turn it back on.

2) Smoke Smells

Your furnace is a controlled fire burning in your home. That means all the gasses and smoke from the fire have to go somewhere. That’s what your flue is for! If your furnace’s flue is blocked, that smoke can’t escape, so it’ll stay in your home instead. Sometimes flues can get blocked by debris, but sometimes they can get blocked by animals or bird nests. If your house smells like smoke when your furnace is running, shut it off and give us a call. Our techs can get whatever it is cleared out so the smoke leaves your home again!

You might also be interested in: Dangers of Animals and Your HVAC System

3) Rotten Egg and Sewage Smells

Some gasses don’t naturally smell like anything. That’s why gas companies actually ADD a stinky odor to natural gas! That way, if you ever have a leak, you’ll be able to smell it and know things aren’t safe. All this to say… if you smell rotten eggs or sewage when your furnace is running, it’s dangerous! You probably have a gas leak, and you need to get out and call us to take a look at it right away.

4) Burning Dust Smells

If you just started your furnace up for the season and you notice the smell of burning dust, don’t panic! That smell is normal and will start to go away after a couple days of running your furnace. If the smell doesn’t seem to be getting better, check your air filters—you might be due to change them. If you change your filters, let the furnace run for a few days, and the smell still won’t go away, then it’s time to call us to check it out.

5) Chemical Smells

Did you ever have frog dissection day back in school? If you have, you might remember the gross smell of formaldehyde. If you smell this in your home, it’s likely a crack in your heat exchanger. If that’s the case, your family is at risk of carbon monoxide leaks. Shut your furnace off and have us come out to check it before turning it back on.

6) Pet Odors

If your home suddenly smells like animal urine or wet dog, you might have some pet waste or fur near your furnace registers (the vents in the floor). If you catch a strong animal stink every time your furnace kicks on, check for messes near these vents. Cleaning it up should fix the problem!

7) Moldy Smells

If your home smells like mold or mildew once you start running your furnace for the season, there’s a possibility you’ve got mold on your coils or in your ductwork. Mold can make your family sick and can really bring down your home’s air quality. You can call us out to check for mold on the unit, but if we don’t find any on your system, it’s probably in the ductwork. Unfortunately, Morris-Jenkins doesn’t clean ductwork. In fact, we don’t even recommend having your ductwork cleaned at all! When you clean ductwork, you’re likely to accidentally damage it (it’s kind of fragile). Instead, you’re better off just replacing all of the ductwork, rather than wasting time and money cleaning it, only to end up replacing it when you realize it’s been torn (which can cause all kinds of other issues in your home). Either way, don’t put off dealing with mold in your home!

Bonus: Furnace Doesn’t Smell, but Carbon Monoxide Detector Is Beeping

Your furnace produces a deadly gas that you can’t smell. You can’t even see it or taste it. If your carbon monoxide detector is beeping, don’t assume everything is ok just because you can’t smell gas. If you have a carbon monoxide leak, you won’t be able to smell it. You have to trust your detector, get out of your house, and call for help! We’ll send one of our technicians to figure out exactly where it’s coming from so we can get your home heating safely again. Most likely, the leak is coming from a crack in your heat exchanger.

Don’t have a carbon monoxide detector? Now’s the time to get one! You should have one on every floor of your house. And it’s important to remember to replace the batteries every year and replace the entire detector before it expires. Otherwise, it’s nothing more than a decoration. Here are some of our other recommended furnace safety features.

Related: Flu Symptoms that might actually be Carbon Monoxide Poisoning

HVAC Smells Don’t JUST Come from Your Furnace

Your furnace isn’t the only part of your heating and cooling system that might stink. Your AC can smell funky sometimes, too! If you ever notice a musty stench like sweaty gym socks, that’s actually such a common thing that it’s got a special name! It’s called “Dirty Sock Syndrome,” and it’s what happens when decaying organic material hangs out on your evaporator coil. The smell can come from mold, mildew, and bacteria on your unit. If the space around your unit (most likely your attic, basement, or crawl space) is humid, it’s gonna make this problem a lot more likely. Keep up with filter changes to keep this problem from happening in the first place!

Let Us Take a Look

Sometimes, your nose knows when something’s not right. If you smell something that just doesn’t seem normal when you’re running your furnace—trust your instinct! If it doesn’t seem right, it probably isn’t or if your furnace is blowing cold air. Give us a call (or text us) and we’ll send a technician out to take a close look at everything. Your family deserves a home that’s safe, cozy, and stink-free!

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