Dirty Sock Syndrome in high efficiency HVAC units

I was recently told my new HE HVAC unit has the dreaded dirty sock syndrome.  Never had this problem with the old unit.  My research shows me it is usually tied to heat pumps.  I have a gas furnace.  Research shows mixed opinions on solutions: UV lights, treated coils, etc.  I do not want to fork out any more money if it's not going to fix the problem.  I was also advised to run the A/C with the windows open to clear out the smell.  I did this and it did not work (and now I feel guilty for wasting energy all day).  I was told there is no health threat associated with DSS.  How is this not possible?  I have a 9-month baby in the house and am concerned.  What are my options?  And am I responsible financially for the fix (if there is a fix)?  

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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.

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

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.

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.  

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.

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

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?   

 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.

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?  

My family is going through the DSS, I highly advise you to get a good creditable Enviromental firm to look above the coils for mold in the insolation inside the unit.  Do you by chance have an ERV or HRV installed in your house? Ours was hooked up wrong causing huge health problems. Look into the Fresh-aire web sight. I am probably going to add the filter and the Apco products they offer. 

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

Not certain of the relevancy here but It brought back some memories.  The memories are all from commercial jobs where the overhead metal and flex ducting were dripping water and producing an odor.  Here is what we determined in those cases;

 

Obvious;y, heat travels to cold including convected heat.  In that process, that convected heat energy carries any humidity along for the ride.  This is how some mold problems occur.  The heated air travels to a cold wall along with some of the humidity.  Heat energy goes through the wall, at least the upper 2/3 of it.  The bottom 1/3 stays colder than the top and that area stays wet.  Mold grows on the bottom 1/3 of the wall.  There has to be moisture present for the mold to grow.

 

Having said that;  we found the same thing happening in ducting.  The hot air travels through the ducts.  That heat energy travels through the insulation / noise reducing material inside the ducts.  Some of the humidty carried with it stops at the metal / plastic.  That water runs downhill, ponds at low spots, finds small cracks, etc.

 

Standing water tends to smell, stagnant water kind of smell.  I would not discount the ducting as NOT being the culprit here for the smell.

 

We applied our RCC to the out side of the AC ducts.  This stopped the heat energy from traveling to / through the ducts.  No more smell, no more built up condensation on the inside in the cold months or the outside of the ducts in the hot months.

 

These are commercial cases here but they are not unlike residential systems.

 

Just some thoughts here.

THE RCC CLASSROOM

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