Have you just turned the heat on for the first time in the season and realized your furnace is smelling weird? Maybe it’s the middle of the season, and you’re walking around your home thinking, “Dear God, what is that smell!?”
‎‎
‎‎Fortunately for you, there is nothing new under the sun, and all those smells have been documented. There’s an explanation for that—smells from the furnace are often normal and predictable.

Keep reading and I will go through each possible smell, the reason for it, and possible solutions.

5 Furnace Smells and What They Mean

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.

  • burning smells
  • rotten eggs
  • smoke
  • dirty socks
  • musty
  • 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

A dusty smell is actually quite normal. And to be a bit more specific it often smells like a burning dusty smell. That’s because that’s exactly what it is in many cases.

If you’re smelling this when you’ve just turned your furnace on for the first time in the season, dust may have collected as the furnace sat dormant during the summer.

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 orders are something you should be concerned about. It could be the motor or any other electrical component of your furnace. It could also be your wiring. 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 you smell rotten eggs in your home during the heating season 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 into your home 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, turn your furnace off immediately.

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.

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.

Furnace duct smoke
Smoke coming out of the air vents could mean that the chimney is blocked, so make sure to turn your furnace off as soon as you notice this.

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, creating a breeding ground for mold.

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.

Conclusion

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 . . .

Potentially Dangerous odorsBurning
Rotten eggs
Smoke
Not dangerous odorsDusty
Musty

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, 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.

Hopefully, this has addressed whatever it is you smell in your home.

While you’re here, why not check some of our related posts below. Maybe we can help you with something else.