Dirty Sock Syndrome: Your DIY Fix It Guide

dirty sock syndrome

🧦 What Is Dirty Sock Syndrome?

Dirty sock syndrome is a term used to describe a musty and unpleasant smell that your heating and cooling system can sometimes emit. This rank smell is often described as being similar to dirty socks or other sweaty and stale odors.

This type of smell is a symptom of a combination of dirt, dust, and moisture that builds up on your air conditioner’s evaporator coil.

Without human intervention, the mold and bacteria will build up to a point where you can smell those dirty socks!

You could have dirty sock syndrome if you start noticing that your home smells like your son’s hockey locker room and dirty gym socks when your AC kicks on.

I think it is essential for me to point out at this point that we are not joking.

This is a real problem that homeowners and renters face. It is actually called ‘Dirty Sock Syndrome’ in the HVAC industry.

In the Okanagan Valley, where we run our HVAC business, we get questions about this from time to time.

Usually, it’s at the start of spring when people transition from heating to cooling.

This blog will quickly explain what dirty sock syndrome is, what causes it, whether is it dangerous, and what you can do to eliminate it.

🧦 So, What Causes Dirty Sock Syndrome?

Dirty sock syndrome is that foul odor coming from your heat pump or AC when you first turn it on.

It is caused by the build-up of bacteria and mold from organic materials that found a home on your evaporator coil.

These bugs can grow due to the moisture in the air that builds up on your coil over time.

This is further fueled by the dust that collects in your HVAC equipment from inadequate filtration and is especially common when your AC hasn’t been used in a while (aka winter).

In parts of the US, including Canada, it is not uncommon for people to use their heating system at night and switch on their air conditioner or heat pump in the afternoon.

This heat, combined with dust and moisture in the darkness of your HVAC unit, is the perfect recipe for dirty sock syndrome.

This is why it’s important to adequately filter the air entering your HVAC system.

But did you know that replacing your AC filter isn’t just for you?

It’s for the health and well-being of your AC as well!

Related Reading: Everything You Need To Know About Your Furnace Room

☠️ Is Dirty Sock Syndrome Dangerous?

Dirty evaporator coil
A Dirty Evaporator Coil pulled from a customer’s HVAC System

The short answer is that it depends. Usually, the answer is no.

Dirty sock syndrome is not dangerous.

Dirty sock syndrome is caused by mold and bacteria growth, none of which are harmful to your family’s health under normal circumstances, and no one in your family is immunocompromised.

What can be dangerous is when mold takes hold inside your cooling system and starts to grow and spread.

Mold can be a health risk that needs to be handled appropriately.

However, as a general rule, the CDC reports that most molds are only mildly toxic to humans and that health symptoms rarely progress past chronic coughing and wheezing, even in the most heavily infested homes.

This is obviously not what you want, so mold should be adequately handled or reported to your landlord ASAP.

It is important to remember that even if you have dirty sock syndrome, it doesn’t mean you have mold.

So don’t freak out yet; open up your HVAC system and see what’s up.

This can become a problem when someone in your household has asthma, severe allergies, or is immunocompromised.

For instance, one of my family members has moderate asthma.

So, therefore, we take mold and allergens very seriously because we have to only use high-quality air filters.

We even clean the evaporator coil once every quarter.

We’ve also added a stand-alone air purifier in many of the bedrooms and fitted our indoor air handler with a UV air purifier just to be safe. This system works great for us.

Every household is different, so it’s worth researching further to see your options.

An AC smelling like dirty socks doesn’t automatically mean that you are growing a mold farm.

Though it does mean that the right conditions exist for it to grow and thrive.

The following section will address how to deal with a smelly air conditioning system.

Dirty sock syndrome isn’t usually dangerous, and it isn’t going to kill you.

However, you should still address it before it becomes a bigger problem. Plus, who wants to live in a house that stinks?

For more information on mold and the possible side effects of living with mold, take a look at this CDC article.

🛡️ The Easy and Cheap Solutions First.

Checking evaporator coil

Before attacking the issue, it is essential to rule out other possibilities before concluding that you have dirty sock syndrome.

So here are a few things to rule out before calling your local HVAC contractor:

🔧 Condensate Drain

Make sure your condensate drain pan is empty. If it’s full, empty it and check your condensate drain line for blockages.

🔧 Air Filters

Check that your AC filter provides the proper filtration for your AC and is not moist. If it is wet, replace it immediately.

🔧 Drainage

Check and clear any HVAC drainage lines that could be obstructed.

Some moisture in your HVAC system is common, but excessive moisture is a significant problem.

After completing this and finding that there’s still a foul smell when your AC or furnace turns on, it’s time to call your local and trustworthy HVAC technician.

🛡️ How to Prevent and Treat Dirty Sock Syndrome

Residential Central Air Conditioning System Layout

🧰 Invest in a High-Quality Filter

The most significant factor in preventing dirty sock syndrome is fitting your air conditioning system with a high-quality air filter.

The same logic can be applied to heat pump systems as they operate like an air conditioning unit.

Bacteria, mold, mildew and bacteria need dust and other porous substances to live on to thrive.

So removing these from the equation before they get into the system and onto your evaporator coil is one of the best ways to tackle dirty sock syndrome.

There are some caveats in upgrading your AC filter, so it’s best to read this first: Air Filter Guide. MERV Filter Ratings and What They Mean For Homeowners.

🧰 Embrace UV Technology

The second way to prevent these smelly bugs from growing on your evaporator coil is to use a UV light air purifier.

These UV purifiers have been used for decades in hospitals and are proven to kill bacteria and mold quickly.

At Phyxter Home Services, we recommend the installation of a UV air purifier for any customer that reports asthma problems, allergies or a family member with a compromised immune system. 

Ask your HVAC contractor if you have a problem with any of these.

Several companies on the market make UV air purifiers, but we have always been a fan of Honeywell. They make quality products and are reliable.

We also like the REME Halo Whole Home In-Duct Air Purifier.

🧰 Add a Dehumidifier to Your HVAC System

Whole-home dehumidifiers have many benefits for your home, especially if you live in humid areas.

The key focus here is on improving the comfort of your home and removing excess moisture that leads to dirty sock syndrome.

One of the benefits of air conditioning is that it is designed to remove excess moisture.

Though too much humidity can overwhelm your AC if it isn’t running efficiently. You can lighten the load on your AC by adding a dehumidifier to your HVAC lineup.

🛡️ How to Treat Dirty Sock Syndrome:

I have some bad news: you can remedy the situation by a thorough cleaning of your air conditioner cooling coils, but that’s not a guarantee.

The only way to 100% eliminate that unpleasant smell is to replace your evaporative coil.

Depending on your air conditioner’s age, replacing your entire HVAC system may just be a good idea and a cost effective one as well.

But first, try the easy and cheaper options and see if that helps!

  • Start by checking your condensate drain pan for standing water and ensure it drains correctly.
  • You can buy dissolvable tablets at any hardware store or online to keep these drains clean and clear.
  • After ruling out the drainage issue, check for other possible contributing factors.
  • Start by adding the preventative measures we talked about previously:
  • Replace your air filter with a higher-quality filter
  • Add a UV air purifier
  • Add a whole-home dehumidifier
  • Get your duct system cleaned

These are essential additions to keep dirty sock syndrome at bay and keep your HVAC system clean.

The added bonus is that these measures will help improve indoor air quality.

Next, you’ll have to clean your indoor evaporator coil to eliminate the dust, mold spores and bacteria on your evaporator coil.

new evaporator coil

🧹 Get Your Ductwork Cleaned

Not only do mold and bacteria accumulate in your indoor air handler, but they will also find their way into your duct system.

This is particularly bad in the corners and joints of your ducts, as the airflow isn’t uniform. 

As mentioned, this is compounded if you have had air filtration issues and have not been replacing your filters regularly or using the wrong type of filter. 

If your filter has not successfully captured all the bad stuff, then you will have issues inside your ductwork which can be hard to find.

A decent cleaning of your ductwork will remove the bacteria and mold causing that horrible smell in your home.

🧹 How to Clean Dirty Evaporator Coils:

Evaporator coil inside an indoor air handler
Evaporator coil inside an indoor air handler

We won’t go into too much detail here because we have already written an extensive guide on coil cleaning.

But, generally speaking, cleaning a dirty evaporator coil is best left to an HVAC systems technician.

This is because they are easy to damage and costly to replace.

🧦 Final Thoughts on Dirty Sock Syndrome

Phyxter Approved Logo on Service Truck

Is dirty sock syndrome dangerous? Not usually, but it can be annoying and downright embarrassing.

After all, who wants their house to smell like a locker room?

These smells and odors directly result from the mold and bacteria that can collect inside your air conditioner.

But luckily, there are several ways to prevent and stop the smell of dirty socks and improve your indoor air quality.

If you have tried all of the easy fixes above and can still smell dirty socks, it’s time to schedule an in-home maintenance visit from your local friendly HVAC technician.

Ready to schedule your next HVAC service and live in the Okanagan area?

Give Phyxter Home Services a call. We’d be happy to help you in any way we can.

Dealing with other common AC problems? Check out: Top 18 Common AC Problems and Solutions

Russell Jones

Russell, a native Australian and VP of Operations at Phyxter Home Services, is also part-owner of Vernon Air Conditioning, Plumbing, and Electrical Services. When he's not busy with work projects and renovations, Russell enjoys putting his vast knowledge of home improvement to good use by sharing his tips and tricks.

About our blog

Phyxter (pronounced Fix-ter) is a national home services brand specializing in Residential HVAC, Electrical and Plumbing solutions.

Phyxter is laser-focused on writing the best articles and guides to empower homeowners to get the best out of their homes.

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