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Why Does my Furnace Smell?

If your furnace is starting to smell a little funny, don’t worry – you’re not alone. A lot of homeowners have the same issue from time to time with their heating and cooling systems. What can you do about an odd furnace smell? And more importantly, what’s causing the smell in the first place? Star Heating & Cooling explains the likely causes behind common furnace odors.

Why Does My Furnace Smell?

Do you ever notice that your furnace smells when it’s running? Strange furnace smells can be caused by a number of different things, and it’s important to be able to identify them so you can take appropriate action and schedule repairs. Here are some of the most common furnace smells and their causes:

Burning Plastic

A burning smell is usually caused by wires that have come into contact with one another and are burning. If you notice this smell, it’s important to shut off your furnace immediately and call a furnace repair technician.

Burning Dust

Dust can accumulate on the furnace over time, and when the furnace turns on, the dust can burn to make the furnace smell. This burning smell when you first use your furnace for the season is usually not a big deal, but if it’s particularly strong, it’s a good idea to have your furnace serviced so that the buildup of dust can be removed.


If you have ever noticed a musty smell coming from your HVAC system, it is likely due to mold. Mold loves warm, moist environments, and a furnace can provide the perfect conditions for mold to thrive. In most cases, the mold will be growing on the furnace filter, which is why it is important to regularly change your furnace filter.

Mold can also grow on the furnace itself, particularly in areas where there is condensation. If you notice mold on your furnace, you will need to clean it off with a bleach solution. However, it is also important to try to improve the air circulation in your home to prevent mold from returning. Make sure that the air vents aren’t blocked, and consider using a dehumidifier.


The heat exchanger is a crucial part of the furnace that helps to transfer heat from the combustion chamber to the air that is circulated throughout the home. A crack in the heat exchanger can cause formaldehyde odor to be released into the air, leading to that furnace smell. A cracked heat exchanger poses a huge risk of carbon monoxide exposure in the home. In some cases, a cracked heat exchanger can also be a fire hazard. If you notice this furnace smell, turn off the furnace and call for repairs right away.


If you notice a smoke smell coming from your furnace, it could be caused by a blockage in the flue. The flue is the vent that carries exhaust gases out of the furnace and into the atmosphere. If it becomes blocked, those gases can build up inside the furnace and eventually escape through any cracks or openings. In addition to being a fire hazard, this can also be a health hazard, as some of those gases can be toxic. If you think there might be a blockage in your flue, it’s best to call a professional for help immediately.

Furnace Repair Services in Fishers, Indiana

If you’re ever wondering, “why does my furnace smell?” it’s always best to err on the side of caution and call an HVAC system repair technician. Star Heating & Cooling is able to diagnose the problem and get your furnace back up and running safely in no time. Contact us today to schedule a furnace repair appointment.