What is “Dirty Sock Syndrome?”

Indoor Air Quality

What is “Dirty Sock Syndrome?” 

I get calls on a regular basis either asking about “dirty sock syndrome” or describing their problem as “dirty sock syndrome”. In reality, in the last 5 and a half years, we have only seen it twice.  Yes, they do have a musty or mildew type odor coming from their HVAC system, but no, it is not “dirty sock syndrome”.

Most professionals agree that “Dirty Sock Syndrome” is caused by a bacteria that collects and grows on the indoor coils of heat pumps and air conditioners.  Complaints normally surface when heat pumps go into defrost, or when systems are run in heating for a brief time then switched back into cooling. The bacteria or odor collects and grows on the coil during this heating time and is released all at once when the indoor coil gets cool and damp.

Since many odor problems are incorrectly labeled as a dirty sock problem, it is important to eliminate fungi and mildew from the coils, supply plenum and air handler cabinet, dirty drain pans holding water, drain lines connected to plumbing systems without adequate traps or dry traps, return air leaks in ductwork or chases to properly identify the problem. If the odor is present all the time, especially during the heating cycle, the problem is NOT dirty sock syndrome.  Dirty sock complaints only smell when the indoor coil gets cool and the bacteria releases its odor.

A thorough cleaning of the evaporator coil will bring the system back to normal and will usually prevent a complaint for the rest of the heating season.  The majority of complaints are resolved with a thorough cleaning.

If the coil cleaning does not resolve the complaint, the next suggested action would be to contact Power Vac America.  There are HVAC companies that can pull the coils and dip the coils in a vat to kill the bacteria and apply a protective coating to prevent the bacteria from growing.  As a last resort, you will have to replace the coils.

Even though your problem might not be “dirty sock syndrome”, your odors and smells are real.  A thorough cleaning of all of the air handler unit components, including the coils, to eliminate the source of the odor causing dirt, debris, fungus and bacteria should solve the problem.  Call Power Vac America today for a free estimate.

We want to hear from you! Call or email to tell us about your indoor air quality problems.  We’ll help you find the right solution.