Dirty Sock Syndrome in high efficiency HVAC units

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Permalink Reply by Bob Kretvix on February 2, 2012 at 6:58am

Dirty Sock Syndrome is actually caused by a combination of bacterial "slime" (biofilm) and mold, such as yeasts, that typically grow on the coils of the unit.  The biofilm has been described as being like the slippery, slimy surface that develops inside a pet's water bowl. I think you would agree that is not significantly hazardous either.

I have tested for it (mainly mold) in several instances and have read similar accounts.  Essentially the mold spores do not easily become airborne, perhaps because they grow in the slime, nor are yeasts generally considered particularly hazardous.  Therefore it is rare to even detect the mold in air samples.  The bacteria is also not of a concern other than the odor it creates.  Unfortunately I have not read of any surefire long-term remediation method either.

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Permalink Reply by Ti Mougne on February 2, 2012 at 8:42pm

Thanks Bob.  Glad to read your thoughts on the low health risks associated with DSS.  

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Permalink Reply by Andrew McDowell on February 2, 2012 at 7:02am

I had a customer who came to me about DSS.  She had been looking for an answer for several years, after trying ultraviolet lights, filters, bleach, etc.  The smell only occurred in the fall, after the cooling season.  I found some flex duct returns that had a low spot where moisture accumulated and didn't drain. In any case, she had the ducting removed entirely, replaced with steel ducts, and the DSS disappeared.

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Permalink Reply by Ti Mougne on February 2, 2012 at 8:49pm

Thanks Andrew, but I'm not sure I'm ready to go this route.  It seems like I would have experienced DSS with my previous unit if the problem is in the ducts.  

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Permalink Reply by Cameron Taylor on February 3, 2012 at 11:48am

Your mention of the low spot in the flex ducting collecting water (thereby soaking the insulation at some point, most likely) makes me wonder if internal duct lining may contribute to DSS. The OP is puzzled by his DSS in that he's running a gas furnace instead of a heat pump, where DSS problems are commonly reported.

That your customer had her ducting replaced with steel ducts, and with the assumption said ducts were externally insulated vs. internally insulated, makes me think internal lining of ducts remains not to be a good idea.

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Permalink Reply by Stan Kuhn on February 2, 2012 at 8:27pm

Was the AC coil and drip pan checked for mold?  That would be the easiest fix.

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Permalink Reply by Ti Mougne on February 2, 2012 at 8:54pm

No, actually the service tech gave me his diagnosis just by asking me questions.  We have since called the dealer back and they are sending someone else out to further assess the situation.  I will definitely make sure they check the coil and drip pan for mold.  The gentleman on the phone said they may need to order us a new coil.  

I'm still perplexed as to why this is happening since we have a gas furnace and all my research ties DSS to heat pumps.  Research has also shown that DSS is common with high efficiency units.  Any thoughts as to why?   

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Permalink Reply by Stan Kuhn on February 3, 2012 at 7:42am

 I would keep good tabs on effects on your baby as a first priority.  Coils can be cleaned, they don't have to be thrown away when dirty.  Has your heat run since the furnace was installed?  You stated that you ran the AC but didn't mention the heat.  My GUESS as to the reason for the problem with heat pumps is that they generate a low temperature heat vs. a gas furnace, and the higher temperatures of the gas furnace may kill mold spores on the coil.  If the heat hasn't run, try it.

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Permalink Reply by Ti Mougne on February 3, 2012 at 11:18am

Thanks Stan. I am still very concerned about the effects on my baby... almost to the point where I don't want to run the A/C until this problem gets resolved.  Seeing how we live in Texas, this could be challenging.  

And to answer your question... we have been using the gas furnace all winter, which is why I don't understand why we're experiencing DSS.  We've had a few warm spells this January and have turned on the A/C, which is when we notice the smell.  Is it possible that it's the high efficiency of the gas furnace that's preventing the temperatures from getting hot enough to kill the mold spores?  

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Permalink Reply by Doug Hefernan on October 11, 2012 at 9:40am

There is a cure for Dirty Sock Syndrome.  You may not find long lasting results with chemicals, and UV light may not be effective.  A deposit of an antibacterial must be left on the coil, or it will eventually come back each time the coil gets wet.

 

The cure is not expensive or difficult to apply.  What you need is a very dilute solution of pine oil.  See link or search, "Dirty Sock Syndrome" in YouTube:

http://www.youtube.com/watch?v=VclGuogRPCY

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