Is my furnace filter making my house smell musty?

    October 19, 2021 Reid Geiler

    Is my furnace filter making my house smell musty_furnace filter_the geiler company

    Nobody wants to live in a stinky home. But sometimes, finding the cause of a stench can be more complicated than you’d expect. It helps to narrow it down to location. If it’s powerful with the HVAC system turned on, you can be confident that the smell has something to do with that. In fact, it might be that your furnace filter is making your house smell musty.


    With the busy Holiday season right around the corner, now is the time to address the stench. Let’s look at why your furnace has started smelling musty and how to fix it. With a few cleaning and maintenance tips, you can keep your house smelling fresh throughout the winter. Your family and your Holiday guests will thank you!


    Narrowing down the smell


    It’s common and normal to smell a different odor from your furnace when you first turn it on. After months of sitting unused, a furnace will often emit a faint burning odor. That’s the smell of accumulated dust burning away.


    Like any item in your home, the furnace gathers dust and dirt during its time off. When the heat starts up again, it’s normal to notice a smell. This smell should last for just a few hours, and should have a familiar smell from last season.


    You might also notice a musty odor when you start up your furnace. This could be coming from a damp section within the system. Often, running the furnace will end up drying the dampness and clearing the smell.


    If there’s a musty smell hanging around long after you turn on the furnace, that’s a different story. In that case, you may have mold or mildew somewhere in your furnace system, which you should address ASAP.


    What causes mold and mildew in a furnace?


    Discovering mold within your HVAC system is a pretty common problem. Mold and mildew thrive in moist, dark environments, and your system has plenty. The air ducts in your home are dark and tucked away. They may often be covered in condensation, making them susceptible to growing mold.


    It’s not just the ducts that can grow a source of musty smells. Other parts of the furnace are also commonly plagued with mold, like the air filter or the evaporator coil. Mildew is just a natural response to the conditions created within an HVAC system. For this reason, maintenance is important in keeping the air smelling fresh and breathing clean.


    There are some general cleaning tips that will help keep your home fresh, and we’ll share those soon. But when your furnace is making your house smell musty, you should go straight to the source. The only trick is figuring out exactly where the source is.


    Furnace filters


    Air filters are a great place to start when looking for a moldy smell. They get clogged with all sorts of debris, including dust, dirt, bacteria, and mold spores. It’s their job to collect these things from the air so that you don’t have to breathe them. But when they’re full they can’t do their job any more. That’s why it’s so essential to change your furnace filter regularly.

     Is my furnace filter making my house smell musty_furnace filter_the geiler company

    Most professionals agree that you can go about 90 days in between air filters. But, if you live in a home with more than one pet, it’s better to change them more often. It may be that changing your furnace filter more often is the only thing you need to prevent a musty smell in your home.




    Each HVAC system has two sets of coils — the evaporator coil and the condenser coil. A dirty evaporator coil is particularly likely to be the culprit of a mildew smell. You can clean the coil on your own or hire a professional to do so.

     Is my furnace filter making my house smell musty_air coils_the geiler company (1)

    If you decide to go the DIY route, start by vacuuming the coil, then spraying it with a solution of 1 part bleach and 10 parts water. Be sure to clean the evaporator pan as well.


    Air ducts


    It’s entirely possible that it is the air ducts that are causing a musty smell. It might be from mold or mildew, or it could be from an excess build-up of dust, dirt, and debris.

     Is my furnace filter making my house smell musty_air ducts_the geiler company

    You might be able to stop the musty smell short-term by sprinkling baking soda just inside of your air ducts. However, this won’t address the cause of the issue. And, although the odor is unpleasant, that’s not the biggest concern with mold or mildew. Both can cause discomfort and illness if left untreated — particularly for those with allergies.


    If you haven’t been able to find a single solution to the smell in your furnace filter or coil, it might be time to call for help. HVAC professionals like Geiler are here to help locate and resolve the source of a musty smell. We’ve been serving the Cincinnati area for decades and are happy to provide our helping hand.  


    Maintenance tips


    Once you get your home smelling fresh again, it’s smart to stay ahead of the problem with some regular maintenance. Similarly, changing the air filter regularly is essential. Not only does it keep the air clean, but it helps your HVAC system work more efficiently.


    You should also vacuum around the furnace itself seasonally. Clean the nooks of the unit, including its blower compartment. Then, vacuum in and around your air ducts as well as you can. If you’ve never done this before, it might be worth it to have a professional come in and clean the ducts. Professional-grade equipment can do a better job of getting deep into the duct system.


    When you do hire a professional to clean out your duct system, they will inspect for mold. Should they find some in your system, it’s important to address the problem itself. Fix whatever may be causing a buildup of moisture to prevent another musty incident. Once that’s handled, and with a little seasonal maintenance, your HVAC system should be in great shape!

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    You might also want to read:

    Do HVAC filters really help air quality?

    Allergies, Asthma & Indoor Air Quality

    How Often Should I Change My Air Conditioner Filter?

    Is my air conditioning making my allergies worse?




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