Woman plugging her nose because she smells rotten eggs from her gas furnace

5 Common Furnace Odours You Should Know About

Your furnace emits odours naturally that you may not notice, while some may be so subtle that they’re not that bothersome. However, there are odours that can indicate a serious problem, which requires immediate attention. In this post, we’ll talk about the most common furnace odours and the causes behind them:

1. Burnt Smell

Your furnace can collect dust and debris when it’s not in use. The accumulated dust burns away when you turn on your furnace; in turn, it will produce a burnt smell.

Most of the time, burnt odour isn’t a problem because after a few heating cycles, the odour will clear up on its own. Usually, the smell is due to burnt dust, and to prevent this, dusting and vacuuming your furnace will help eliminate surface dust and minimize burnt smells.

2. Musty Smell

More often than not, your furnace will emit a musty odour when you turn it on, especially if the equipment shares the same air handle as your split AC unit. Usually, the smell is because the system hasn’t been used for a while. Another reason is that the air filters may be dirty or clogged.

Resolve this by running the furnace for a few heating cycles that can help dry up dampness to get rid of musty odours. If it doesn’t go away or it becomes even stronger, then it’s likely you already have mould and mildew growth there. In this case, it’s best you hire a professional to work on it instead.

3. Oily Smell

The oily smell comes from an oil-fired furnace that can emit unwanted odours. This usually happens due to oil spills that occur during furnace refuelling. With that, the smell can linger for a few days before it goes away. However, it’s best you have the furnace inspected to ensure no other issues could damage the system.

4. Noxious Smell

When the exhaust chimney is partially or completely blocked, it can redirect noxious exhaust odours into your home. Not only that, chimney blockages can cause carbon monoxide to build up inside your home, which can be dangerous. If you notice this smell, make sure to check and clear all obstructions thoroughly.

5. Rotten Eggs Smell

Natural gas and propane are odourless, which is why suppliers add methyl mercaptan to the gases for easy detection of leaks. Unfortunately, the compound smells like cabbage or rotten eggs.

So, the only time you could smell this in your home is if you have a probable gas leak. If you smell a gas leak, shut down your furnace and get out of your house right away. Call the local gas company or fire department to shut down your home’s gas supply and to trace where it’s coming from.


Furnace odours are good indicators of your system’s overall condition. Therefore, it’s essential you be mindful of these odours, and you know what to do when you catch a whiff of any of them. That way, you can prevent bigger problems that could cause damage to your home and your bank account.

Here at Bromac, we offer plumbing and heating solutions, such as leak detection services, for residential and commercial properties in the Lower Mainland and Fraser Valley. Contact us today!

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