If you start to notice an odd smell coming from your furnace when the heat turns on, it is time to make a maintenance call. It could be something minor like a dirty filter, or it could be a serious issue like a faulty electrical component. Because it is tricky to determine the severity of a furnace odour, you should not put off getting it checked for too long. Avoid causing extensive damage by finding the source of the stench as soon as possible. Here some known smells a furnace can give off and what they could mean.


A smell similar to formaldehyde might mean a cracked heat exchanger. This element is responsible for transferring heat from the combustion chamber to the furnace plenum. If the heat exchanger becomes cracked, harmful carbon monoxide fumes can travel throughout your home’s duct system. That is why you should be wary of any chemical smell and seek help immediately.


Worn bearings can cause the blower motor to struggle to work, which can cause your furnace to smell like an overheating motor. It makes the motor use excessive voltage, causing it to overheat. This, in turn, can cause wires to melt, creating an electrical hazard. Turn off your furnace and call an HVAC technician if you smell a burning electrical odour throughout your home. They can inspect your furnace and fix any malfunctioning parts before it causes more severe damage to your furnace and, more importantly, your health.


Another type of burning smell you might notice when you first start up your furnace as the weather gets colder is burning dust. This can collect over warmer months but usually burns off when the furnace is started up again. It is normal for the dust to burn off and should not be a cause for concern. This smell should pass in a few hours but, if the problem persists, check your air filters – they may need changing.


This type of odour is also common when you first start your furnace again in the fall. It usually stems from dust or dirt that has collected in your air ducts. It then blows throughout your duct system when the furnace is turned on, leaving your home smelling like a damp basement. It should subside in a few hours but, if it does not, you may need to change your air filters. A musty smell could also be a sign for mould that has developed on the furnace filter, humidifier panel, or air conditioner coil.

Rotten Eggs

This odour is hard to ignore and for a good reason. It is an indicator that there could be a natural gas leak nearby and you should have it taken care of immediately. Open windows and doors to let in fresh air and evacuate your home right away. When you are standing away from your home, call 911 first and then your gas company. Natural gas is dangerous because it is extremely flammable. A flame or tiny spark could cause a fire or explosion. The sulfuric or rotten egg smell that usually signals a natural gas leak is not a natural component of the compound. It is added to natural gas running throughout homes to help people identify a leak because of its potential danger.


To make sure the strange smell is not dangerous, call the furnace experts Home Comfort Center. Our experienced professionals can pinpoint the cause and find a solution so that your home will smell fresh again and be safe to live in.

Home Comfort Center

Home Comfort Center