Air Conditioner Smell-Dirty Socks Syndrome: Causes and Solutions

Dirty sock syndrome is caused when there’s a buildup of bacteria and mold on the evaporator coil inside your air conditioner or heat pump, creating a musty, dirty sock smell.

This bacteria growth causes the air around it to smell, and the movement of air through your ductwork carries this smell throughout the home.

To be clear, mold and mildew can exist elsewhere in your home and create similar smells. But this refers specifically to the problem within the AC unit.

The reason the evaporator coil is susceptible to this buildup is that, as the name suggests, it’s absorbing moisture to be removed from your home. This is a large function of your air conditioner, and if there are issues with it, buildups of condensation can occur that lead to organic matter spreading.

Dirty sock syndrome is a term for the unpleasant, musty, or moldy odor that can emanate from an air conditioning or heat pump system when it’s turned on. This odor is caused by mold and bacteria growth on the evaporator coil, which is a key part of the HVAC system. 

What Else Could be Causing Smells in My Home?

Dirty sock syndrome, and the specific buildup of organic material that leads to it, isn’t the only thing that can cause a smell in your home.

So what else could it be?

We can’t answer this definitively for each household, but here are some common culprits:

• Faulty equipment
• Water buildup somewhere in your system
• Clogged filter
• Mold or mildew elsewhere in your home
• Large deposits of dust and debris in your ductwork.
• Plumbing issues (water heater, garbage disposal, toilet, etc.)
• Faulty sump pump or sewer line backup

How to remove musty odors from your air conditioner

If your system already has problems, this situation is worse than the above. However, it can still be fixed through deep cleaning.

Some of the same advice applies. You may want to upgrade your filter. You should consider either a dehumidifier in your basement and/or a UV light in your HVAC system.

If there’s a buildup on your evaporator coil, though, the only way to get rid of it is to technician come to your home and thoroughly wash and treat your coil.

Once this step is done, it’s important to realize why it happened, which likely relates to the items we mentioned above like dirty filters or high humidity. Identifying the problem and fixing it is necessary to avoid repeating the problem.