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Jan 17 2023

Why Does Your Furnace Have a Weird Smell?

When you first turn on your furnace and it starts to warm up your home, you might notice a strange smell. A furnace can have many different smells, but most of them are caused by common problems that are easy to fix. At Rooter Hero Plumbing & Air, we provide reliable furnace repair and furnace replacement services for local customers. Our team enjoys helping clients improve the safety and efficiency of their heating systems, and we want you to enjoy the same great results from your appliance. If you’re unsure what is causing strange odors when you use your furnace, keep reading. This article will help you determine whether or not you need to call an HVAC company for an inspection.

Mold or Mildew

Mold and mildew are common household nuisances that can grow on many surfaces, including your heating system. The smell could be coming from a damp filter, dirty coils, or even mold growing inside your ductwork. The first step is to have your filter changed. If that doesn’t fix the issue, then you may need to have your coils inspected, or have your ductwork professionally cleaned.

Rotten Eggs

If you smell something akin to rotten eggs coming from your furnace, it may be a sign that your home has dangerous levels of carbon monoxide. Carbon monoxide is an odorless, colorless gas that can cause severe health problems and even death. Utility companies add a substance called mercaptan to natural gas so that property owners can more easily detect a leak. The first thing you should do if you smell this odor is turn off all combustion sources in your home. This includes any gas appliances such as a furnace or stove. Then evacuate the property and immediately call 911.

Sour Scent

When your furnace has a sour smell, it is likely due to an issue with the heat exchanger. The heat exchanger is an important part of your furnace because it transfers heat from the combustion chamber to the air blown into your home. This will cause problems with your furnace's efficiency and performance, but it can also expose you and your loved ones to unsafe amounts of carbon monoxide gas. If you notice this smell, leave the property and contact an HVAC company right away.


The first time you use your furnace in the fall, there might be a dusty smell. This is because your system has accumulated dust and debris over the past several months while it was sitting idle. This is normal and is not a sign of poor maintenance or improper functioning. If it lasts longer than a day, then there might be some other issue occurring, and you should consider calling an HVAC specialist.


If you notice a strange smoky smell coming from your furnace, your flue may be blocked. The flue is a pipe that runs from the top of your furnace to the outdoors. If it's blocked, gases can't escape properly, leading to odors and the buildup of dangerous contaminants. An HVAC technician can inspect your system, and clean out the flue if necessary, so you can have a safe and effective furnace again.

Burnt Plastic

When your furnace starts to smell like burnt plastic, it's time to investigate. The smell could be coming from overheated electrical components or a faulty fan motor. Ignoring the issue could put you at risk of an electrical fire, so it’s important to get your unit inspected as soon as possible.


Oil furnaces can sometimes have an oily smell because of a clogged filter. In most cases, simply swapping out the old oil filter for a new one will remedy the situation. If it persists, then there’s a chance that oil is leaking from your system, in which case, an HVAC professional can repair the problem for you.

Need Furnace Repair or Furnace Replacement Services from a Local HVAC Company?

There are many reasons why your furnace might be giving off a strange odor. A professional can help you identify the problem and fix it for good. At Rooter Hero Plumbing & Air, we're here to help you get your furnace back to normal. Our team of experts can help determine why the smell is there and find a solution to get rid of it. Contact our office for more information or to schedule an appointment today.

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