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How to Remove Musty and Moldy Air Odors From Your Vents

Everyday Green is a serious DIY addict who loves to help others find different ways to live frugally.

Have you been trying to figure out how to stop smells from coming through vents in your home? This article provides some troubleshooting tips for finding the source of musty and moldy odors coming from your air ducts and what you can do about it.

Have you been trying to figure out how to stop smells from coming through vents in your home? This article provides some troubleshooting tips for finding the source of musty and moldy odors coming from your air ducts and what you can do about it.

Stop Smells From Coming Through Your Vents

While heating and air conditioning systems are a godsend in the hot summer months and on cold winter nights, they can become a nuisance when they spread a musty odor throughout the house. After a few hours, you may find yourself asking: "Can I clean my air ducts myself?" The answer is a qualified yes.

There are a number of reasons why musty smells might be coming from your air ducts system. But the most common cause of a musty smell in ductwork is the presence of mold in your HVAC system. This article will guide you through the process of finding out whether or not you have mold in your air ducts and what you can do about it.

How to Get Rid of Musty Odors Coming From Your Air Ducts

Here are the main troubleshooting methods covered in this article for getting those musty and moldy odors out of your ductwork:

  1. Clean your malfunctioning air conditioner unit because it has A) a dirty evaporator coil, B) a clogged condensate drain line, or C) a filthy air filter.
  2. Install duct filter pads in your vents to control the smell.
  3. Apply DIY odor-control methods such as baking soda to your air ducts.
  4. Consider that the problem may be bigger than something you can solve, necessitating the hiring of a professional service to address the issue.

How to Clean Your Air Conditioning Unit

Cleaning your air conditioning unit is one possible way to eliminate the musty smell from your ductwork. Here are the usual problems affecting AC units that lead to moldy smells and what you can do about it:

Solution 1: Clean Your Evaporator Coil

The evaporator coil is an essential component of your AC unit and the main part that actually cools your home. But when it gets dirty, it becomes the perfect place for mold to grow. Follow these instructions to clean it out:

  1. To start, you’ll need a solution of 10% bleach water. This is enough to kill off the mold without doing any damage to the coil system. (Note: It is important to make sure you water down your bleach though, as undiluted bleach can wear down metal. Alternatively, you could also just go with a standard coil cleaner available at most hardware stores.)
  2. Most central air units have an access panel on the back. Take this off to expose the metal fins in front of the condenser coils.
  3. Using your vacuum with the attachment brush, suck up any loose dust or debris from the fins and coils.
  4. At this point, you can also straighten out any bent fins with a flathead screwdriver or a fin comb, which can be purchased at most appliance stores. Remove the fins—they will be held on with four to eight hex screws.
  5. Now spray the bleach solution on the coils and wipe them down. Pull out the collection pan and wipe it down as well.
  6. Reassemble the unit and run it to see if that has taken care of the musty smell.

Solution 2: Unclog Your Condensate Drain Line

When excess condensation forms on the evaporator coil, it drops down into a pan before exiting through a drain line. If this drain line gets clogged, however, then water can back up in the pan, which further increases the chance of mold growth.

If you see water pooling around the inside of your AC unit and it smells musty or moldy, this is probably the reason why. Luckily, you can sometimes resolve this by using a wet/dry vac to hopefully unclog the drain line (and also suck up any pooling water).

If you're not able to unclog the drain line with your wet-dry vac, however, you'll probably need to call a professional to do so.

Solution 3: Clean or Replace Your Air Filter

Sometimes, your air filter can get so clogged up with debris that it inhibits air from flowing through it. This can, in turn, allow dust and moisture to settle in your ductwork, which can serve as a breeding ground for mold.

So if your air filter looks particularly dirty, then it's probably a good idea to clean it. But if a thorough vacuuming and wipe down doesn't cut it, you may need to replace the filter altogether.

Dirty and clogged air filters like this can sometimes be the cause of mold in your vents, which is why it's important to clean or replace them periodically.

Dirty and clogged air filters like this can sometimes be the cause of mold in your vents, which is why it's important to clean or replace them periodically.

How to Install Duct Filter Pads

If the smell wasn’t coming from the air conditioning unit, then it may be coming from any part of the duct system. It may be impossible to find the cause without a snaking camera system, however.

The next best thing to eliminate the smell is by using duct filter pads. These hypoallergenic filter pads are available at most home improvement stores and are made to fit both vertical and horizontal ducts of all sizes.

  1. Simply unscrew your duct vent covers and place the filter pad into the grate.
  2. Screw the cover back on and let the filter catch the offending particles.

How to Use Baking Soda to Reduce Odors in Your Air Ducts

For more immediate relief, the old stand-by trick of putting a little baking soda in a dish and placing it in the smelly area may work. You’ll have to put the baking soda directly in the duct. This will only work if the baking soda comes in contact with the offensive air particles. So, finding a way to expose more surface area to the air will improve results.

Arm & Hammer currently makes a “fridge pack” that has a peel-off side. This will allow you to stand the box up and have a large surface area for the forced air to pass through.

Should You Hire Professionals to Clean Your Vents?

If none of the above options have worked, you can also try more fully cleaning your air ventilation ducts yourself—and this very useful article can help you do that. But if you're not finding much luck with any of the above methods or if the smell seems to be coming from a dead animal, you will probably have to contact a professional air duct cleaning service.

In general, you should consider having the HVAC system in your home cleaned if:

  • You have significant visible mold growth inside hard surface ducts (like sheet metal) or on other components of your HVAC system.
  • You have pests or vermin—dead or alive—in your ducts. This is mostly a safety issue relating to the potential for contracting diseases or being hurt by aggressive animals.
  • Your HVAC system is clogged with substantial amounts of dust and debris.
  • You can't access or see various sections of your air ducts.
  • You suspect that you might have leaky ductwork (that would require professionals to both uncover and repair).

Find Out What Type of Ducts You Have

What kind of cleaning method your HVAC system will require depends on what type of ducts you have. So it's important to first find out what kind of material your ducts are made out of.

The common rigid ductwork materials are sheet metal, fiberglass-lined, and fiberboard. Your ductwork could also be of the flexible kind made from wire coils covered with plastic and insulation. Additionally, your ductwork could be some kind of combination of all of these materials, so it's important to find out what you have before you begin trying to treat the problem yourself.

What to Keep in Mind When Hiring a Professional Cleaning Service

If you decide to go with a professional cleaning service, there are a few things you might want to keep in mind before you decide which company and plan to go with:

  • Do not go with a company that makes big, sweeping claims about the health benefits of duct cleaning. These claims are generally unsubstantiated. Do not hire a company that suggests routine cleaning as part of good HVAC maintenance. Do not go with a company that claims to be certified by EPA, as the latter neither establishes standards for duct cleaning nor certifies any duct cleaning companies.
  • As a general rule, companies that offer full household services for under $100 will usually not cover all of the duct work in your home. Do a bit of research to find a reputable company in your area. Expect to pay at least $150 for a professional cleaning.
  • It's best to get estimates from at least three different companies.
  • If the company says you have significant mold, ask them to show you visual evidence of any mold they find. (This goes for all supposed biological contaminations.) You can even request laboratory confirmation of mold growth if you're particularly skeptical. For around $50, some microbiology laboratories can confirm whether or not a sample sent to them is actually mold or just a substance resembling it.
  • If you're unsure of the reputability of a company, feel free to check their references or even ask them to show you their relevant state licenses.
  • Should a company suggest using biocides for the treatment of mold, make sure to determine whether or not this is even necessary in the first place—rather than just a way to milk you out of more money. And if you decide to go the biocide route, request that the chemicals will only be used strictly according to label directions.
  • Do not allow companies to use sealants unless no other methods have worked or are not feasible.

Works Cited

  1. Chandler, Brynne. Moldy Smell Coming From Air Ducts. SF Gate. Retrieved on 1 November 2018.
  2. Should You Have the Air Ducts in Your Home Cleaned? The Environmental Protection Agency. Retrieved on 1 November 2018.
  3. Musty Smell Coming From Central A/C Vents? Here's Why. Cool Today. Retrieved on 1 November 2018.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2012 Jennifer Hill


John Griffins on April 28, 2020:

A very intuitive blog. It can be difficult to decide which company to rely on. it is important to first do your own research then try to weigh the options to one which best suits your needs...

Aaron Reyes on December 05, 2019:

Wow, so nice blog, especially I really appreciate your explanation about how to clean the AC unit rather I think this must solve people’s worries in second. Well, I also know that some other companies have provided such a fantastic cleaning service with a proper cleaning kit as “FIFTY REASONS” so I would recommend this for people.

Jasper123Tiong on October 07, 2019:

This is super informative especially the one saying that how to clean the air con unit, it solves my worries in a second. I would definitely hire the professionals from as the services offered by them is attentive and fast! It saves my time alot! Check this out!

Vickie on July 20, 2018:

The house stinks very bad! What can I do?

Michael on March 11, 2018:

I haven't clean my duct at all, my kids start having allergies, my friend referred me to "Marius Duct Cleaner" they cleaned my system that was great.

ms B on January 07, 2018:

The apartment in my building had major water pipe burst foul smell coming thru vent all through apartment smells like musty mole

diana on September 13, 2016:

can you have a musty odor in the air ducts without having mold, and will heat kill the mold if there is some? also, the filters that are mentioned will they catch the mold spores if there is mold in the air ducts? I live in apt building we have central air and heating and each apt has a unit in it that runs off the main unit on the roof. no visible mold on the cover or on the duct work that can be seen... reaching as far in as possible there is no dampness felt nor is there any mold in contact. thank you

Lisa Roppolo from New Lenox, IL on October 23, 2014:

My vents I suspect haven't been cleaned in years (previous owner neglect). I'm having a musty smell when the heat kicks on, so I suspect it is coming from the vents and furnace unit. I am having it done professionally this time but these are great maintenance tips going forward!