Your furnace is an essential part of your home that, even though you might not think about it too often, becomes one of the most valuable appliances during winter. Don’t find yourself without furnace this winter, be on the lookout for signs that your furnace might not be working properly. One of the most obvious signs that there’s something wrong is a strange smell coming from your furnace. According to the smell, it can indicate different problems, which vary in seriousness. It can be hard, however, to diagnose the issue on your own, so here’s a guide to help you figure out what some types of smell mean.

Which smells are harmless?

Some odours coming from your furnace are harmless, but that still doesn’t mean you should just ignore them. If the smell is faint, or if it dissipates after a few hours, there is no cause for concern. However, if it lingers for more than a few days it could mean your furnace needs cleaning. If there is a musty smell, it could indicate that moisture is trapped inside your furnace or, if the smell last longer, that mould is growing inside your furnace. Burnt dust is another common, but harmless smell; especially if your furnace is located in a basement. Dust can accumulate while your furnace is turned off in the summer, and then burns when it’s turned back on in the winter. Once the dust burns, the smell should go away. You can also smell burning oil. It usually means that your furnace filter is clogged and that should make the smell dissipate. You should replace your filter at least every three months. Finally, another smell that can come from your furnace is the smell of dirty socks. Yes, you heard us! The smell of dirty socks can indicate bacteria build-up in your furnace often caused by excess condensation. If the smell doesn’t linger, it’s harmless.

Which smells are harmful?

Some odours, on the other hand, can indicate a serious problem in need of professional intervention. If you smell smoke, it may indicate that your furnace’s chimney is blocked and that your furnace is venting smoke through your air ducts instead. A burnt electrical smell usually indicates that the inside of your furnace is too hot, damaging rubber or metal components. Also, chemical smells, particularly the smell of formaldehyde, can mean that the heat exchanger in your furnace is cracked. The heat exchanger is responsible for moving heat from the combustion chamber into the plenum. A broken heat exchanger is a huge fire hazard and could even cause your furnace to leak carbon monoxide throughout your home. Finally, a rotten egg smell means there is most likely a problem with your furnace’s natural gas supply. Though natural gas is naturally odourless, suppliers treat the gas so that it has a strong rotten egg smell and gas leaks are more easily detected.

What to do?

For most harmless odours, you can usually expect them to dissipate after a short period of time. If it’s burning oil you smell, then you should replace your furnace filter. For a dirty sock smell, clean and/or replace the air filter. If the smells linger more than a few days, then it’s time to call in the professionals as the cause could be a bit more serious. When it comes to the harmful odours, you should turn off your furnace when you first detect those smells. For the smoke smell, call a professional to clean your chimney; however, if the smell is too strong or the smoke detector goes off, it could be necessary to evacuate your home while professionals investigate. When dealing with a chemical smell, it could come from a broken heat exchanger, which is a fire hazard and could also cause a carbon monoxide leak in your home. In that case, evacuation is necessary before even calling a professional.

What you need to remember is that if you find that any smell persists, it’s best to not take any chances with your health and safety, and to call an HVAC expert. It usually won’t take much to fix the problem; a simple filter change or clean-up will suffice, but you’re better safe than sorry!