Furnace Smelling Weird? 5 Smells & What They Mean

furnace smells like gas

Are you stuck trying to stop your furnace from smelling weird?

Sadly, this annoying issue is more common than you’d think. Thousands of people struggle with it daily.

This problem needs your immediate attention, since some odors may indicate a major problem.

If your furnace smells like burning, rotten eggs, or smoke, it might mean danger. But, if you smell a musty or dusty odor, you should be fine.

Potentially Dangerous odorsBurning
Rotten eggs
Not dangerous odorsDusty

Don’t worry, though. Read on below to find out what each odor means and how to get rid of them!

5 Reasons Why Your Furnace Might Smell Funny

Let me walk you through a list of all potential smells and what they could indicate.

In some cases, there’s a simple fix. In others, the smell is a symptom of something dangerous and should be dealt with professionally as soon as possible.

In either case, I’ll let you know.

To start off with, here’s a list of some of the most common smells. These are in no particular order.

  1. burning smells
  2. rotten eggs
  3. smoke
  4. musty
  5. dusty

Let’s take into what they might mean.

Man searching in ducts
Strange smells could indicate your system is in need of immediate attention, or simply be a normal part of system operation after a season of sitting idle.

#1 Dusty

If your new furnace smells funny, it’s completely normal.

You see, people often complain about a burning or dusty smell. That’s because that’s exactly what it is in many cases. Dust may have collected as the furnace sat dormant before turning it on.

That dust and dirt will burn away, typically within the first hour or so. If it doesn’t, try the following.

Solution. If the smell doesn’t dissipate within an hour or so, the first thing you should do is make sure your furnace filter is clean.

If you’re still sensing the smell after that, call for service.

#2 Burning Smells

Different from the burning dust smell mentioned above, this could include:

  • burning plastic or metal
  • electrical
  • burning rubber

Not surprisingly, these types of odors are something you should be concerned about.

It could be the motor or any other electrical component of your furnace, or it could also be your wiring.

An electrical or burning smell in particular could be the motor burning or overheating.

Since any of these smells could potentially mean a fire, the first thing you should do is turn off your furnace.

Solution. If you detect a burning smell, cut power to the furnace at the breaker. Do not turn it on again until you have had an HVAC professional do a service call.

#3 Rotten Eggs

If a bad smell is coming from your boiler or furnace, you might want to keep reading.

If you smell rotten eggs in your home, and you don’t actually have any rotting eggs sitting around, don’t ignore this smell.

A sulfuric odor, similar to that of rotting eggs, can indicate a gas leak.

Natural gas itself is colorless, odorless, and non-toxic, but breathing in high levels of it can lead to asphyxia, a condition where your body is deprived of oxygen.

Additionally, it is very combustible, meaning a leak can easily turn into a fire or explosion.

Many utilities add a chemical to natural gas called mercaptan. And it smells like rotten eggs. Since natural gas has no odor, you could have a leak and not be aware of it, so the smell of rotten eggs is to provide a warning.

Solution. If you smell it, turn off your gas at the main line or at your furnace, and then leave. Once you’re out of your home, call your utility’s emergency number to report the issue.

4. Smoke

If your smoke detector sounds, and you determine that the smell of smoke is coming through your HVAC vents, please turn your furnace off immediately.

You see, any smoke from your furnace should exit your home through the chimney, but if your chimney is blocked it may be venting and releasing through your air ducts.

This could explain why your furnace smells funny when the heating is on.

Solution. You should immediately open your windows to air out your house if there’s only a faint smell of smoke in your home.

If you can actually see smoke in the air and the smoke is strong, you should leave your house.

You’ll need to have a professional in to check the furnace and if necessary a professional to get your chimney cleaned.

#5 Musty

Does the air coming out of y our vents smell musty or moldy? If so, there’s a good chance you also have a central air conditioner that shares the air handler with your furnace.

Due to condensation, mold, and mildew issues are more common with air conditioners, but remember, your HVAC system has many integrated parts.

If moisture doesn’t drain properly during the cooling season—probably because of a clogged drain line—it can migrate to your ductwork.

This could explain why your furnace exhaust smells funny.

Once you have mold in your ductwork, any warm or cool air that your blower motor moves will push the resulting odor and spores into your living space.

While mold doesn’t represent a problem for your HVAC system, it could result in problems for your respiratory system.

Solution: First—and assuming you do have central air—check your drain pan. It could be clogged. Here’s a step-by step tutorial to follow, or check out the video below. 

This will get rid of the source of the mold, but if you have mold growing in your ductwork, you’ll need to get them cleaned.


It’s very normal for your furnace or HVAC system to smell occasionally. In some cases, simply running the system for a few hours will dissipate the odors. Other situations are potentially dangerous.

To recap . . .

Of the two not-dangerous odors, dusty smells shouldn’t last for long after the furnace is turned on. And while mold, isn’t dangerous to your HVAC system, you should still find the source and deal with it because it does represent potential health hazards.

If you smell any of the three odors listed as dangerous (burning, rotten eggs, smoke), you should turn off your system and contact an HVAC professional immediately. In the case of rotten eggs, you should also call your utility company.

I hope this article has helped you out today! Be sure to sign up to our email list for free money-saving HVAC tips and advice.

I've been helping homeowners with appliance repair since 2016. Starting out as an enthusiastic amateur, I've since worked with many Appliance, HVAC, and DIY experts over the last 7+ years. My mission is to help fix your appliances and prevent future issues - saving you stress, time, and money. Visit my author page to learn more! Read more