Why Does My A/C Smell Like Dirty Socks?

Spraying can of air freshener to coverup bad AC smells

For those of you who are new to our site, hello! We are a family-owned HVAC business in Bloomingdale, Florida that has been serving the area since 2000. We strive to bring you the best possible service every day. Over the years we’ve found that customers have a lot of questions about how their HVAC’s work, and the better they understand, the better they along with our help can make sure their HVAC’s run for the longest they possibly can.  We like to answer these questions when we can here on the blog.

One common question is about weird smells coming from your HVAC. The query “Why does my A/C smell like dirty socks” is very commonly searched, so don’t worry, you’re not alone!

If you’ve ever had a teenager or been one yourself, you know the foul odor of gym socks left lying around.

If your house smells like one such sock fell into your vent, or like you’re opening up the door to a gym after a basketball game, you might have Dirty Sock Syndrome. While this might sound like a fake illness you threaten your kid with getting to prevent them from wearing the same socks all week, it’s actually something that happens inside of your HVAC system. It can be very upsetting when you go to turn on your system to relax inside your nice cool house, to smell such a musty, unpleasant and inescapable odor. But don’t worry, we’ll get to the bottom of why this happens, how to fix it, and how to prevent it from happening in the future!

Dirty Sock Syndrome usually starts at your evaporator coil. Your evaporator coil is a very crucial part of your home’s entire system. This coil is where the heat is absorbed by the coolant in order to produce cooled air. They are typically made from copper, aluminum, and steel, for optimal heat conduction. While it’s called the coil, if you’re trying to get an idea of what it looks like, it’s more like coils. Lots and lots of this metal tubing are coiled on itself to provide more surface area for the coolant to interact with the hot air and remove heat. This is located inside of your air handler (that large metal indoor unit where the magic happens) near the blower.

Imagine this: Warm air flows into the coils where it meets the liquid coolant. As this coolant cools the air, the moisture that was in the warm air is condensed into water. When this moisture reaches its condensation point and becomes water, it drips down the coils, into the condensate pan, which allows the water to be drained either into your sewage system or outside via a condensate line, usually a PVC pipe. The cooled air is then pushed through your system’s ducts and dispersed throughout your home. Because moisture is being dealt with in an enclosed environment, any sort of dust or particulates can provide little places for this moisture to build up inside, and allow mold, bacteria, and mildew to grow. All of this excess moisture is a place where bacteria loves to grow – not only is it moist, it’s warm and dark, and difficult to clean without special tools. There’s basically a tiny flashing sign that says “Vacancy” for bacteria – great family rates!

When your system goes from heating to cooling a lot, this problem is more prone to happen. Here in Florida in the Fall and Spring, some days are still hot enough to need your A/C but it fluctuates and you may need to use your heater for a few days, and then maybe a day or two of using neither, and then switch back to A/C. When your system sits without use, it’s the perfect time for bacteria to party.

While the word “syndrome” may make this issue seem like a deadly health issue, Dirty Sock Syndrome is not known to cause fatalities. It can, however, be much more of a problem to those with compromised immune systems, allergies, asthma.

If the mold gets into the rest of the HVAC system, it can continue to grow and become a health issue for your family. Distributing moldy air throughout your house is pretty counterproductive to conditioning your air in the first place. Here’s what you can do.

What Can Be Done?

Not to worry, this syndrome can be fairly easily remedied, so long as it isn’t allowed to go for too long. Don’t be afraid to schedule a service appointment with your HVAC technician (or just give us a call to see if you need one!). Your technician will usually use a combination of specialized brushes, compressed air, and cleaning solutions.

Before doing this, you want to make sure that the issue isn’t a dirty filter, a clogged drain line, or that there is an issue with your drip pan. If you can visibly see that all of these seem clean and clear of blockages, you should call in the pros.


Of course, much easier than remedying the problem is to prevent it altogether, and if you have it once, you certainly don’t want it happening again. There are a few fairly simple things you can do to help prevent Dirty Sock Syndrome:

Replace your filter regularly

While it may seem like a no brainer, dust and other debris entering your system helps encourage the perfect environment for bacteria, so the first step to avoiding your HVAC system ever having to deal with Dirty Sock Syndrome is just to prevent it from happening. The first thing you can do is something that helps with many other maintenance issues that can arise with your HVAC – keep the filters fresh. Change your filter on a regular basis (not sure how often to change? See our article here on How Often Do I Need To Change My HVAC Filter to prevent particulates from entering your system and dusting up your coils. Not only can dust lead to bacterial growth, as it coats the coils it creates a barrier between the coolant and the warm air, making it more difficult for your entire system to successfully and efficiently reduce the heat.

Consider using a “media filter” – these air filters are thicker than your basic filter and remove more particulates from the air without reducing airflow, keeping your system cleaner.

Routine Scheduled Maintenance

Having a trained technician inspecting all those dark nooks and crannies as well as cleaning things up once or twice a year can really go a long way toward improving your home’s indoor air quality. It’s our recommendation that you have two visits annually with at least one of the visits containing a thorough cleaning in addition to the routine inspection.

Keep your ductwork clean and well-sealed

If your ductwork is coated in dust, it’s going to be allowing dust into your entire system. Having it cleaned when needed (don’t worry, we do that as well, so you don’t need to go climbing around in your system!) and having any leakages sealed can go a long way to reducing dust and other particulates.

Install a UV purification system

Because your evaporator coil usually has lots of dark nooks and crannies, and mold loves to grow in the dark, it can be beneficial to install an ultraviolet purification system. These are UV lights that are designed to fit this specific spot and will prevent bacteria from being able to thrive and cause smells such as Dirty Sock Syndrome inside of your HVAC system.

As always, don’t hesitate to contact us if you have any questions!



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