Do you get whiffs of odor that come out of your heating and air vents that smell like dirty socks? If you do, you are not alone. In fact this phenomenon has a name…Dirty Sock Syndrome. This unpleasant odor is musky, and dirty and resembles a locker room smell. Dirty Sock Syndrome is caused by bacteria that collects and grows on the indoor coils of heat pumps and air conditioners.Typically this odor surfaces when heat pumps go into defrost or when systems are run in heating for a brief period of time and then switched back into cooling. The bacteria collects and grows during the heat cycle and then is released all at once when the indoor coil gets cool and damp. Heat pump owners notice this smell when the system goes into defrost, usually when the outdoor temperature drops below forty degrees. This problem can occur when the air conditioner is turned back on after the heating has been used.
It is important to identify the problem before taking action against at as many indoor odor problems are labeled as “dirty sock syndrome” incorrectly. To make sure that “dirty sock syndrome” is in fact the problem you have, eliminate dirty drain pans with water, return air leaks in ductwork or chases, correct drain lines connected to plumbing systems without proper water or dry taps, and make sure there are not any dead animals in the ductwork or near the living space. If the odor you are experiencing is present all the time, it is definitely not dirty sock syndrome. The “dirty sock” odor only occurs when the indoor coil gets cool and the bacteria releases its odor into the air.
To eliminate dirty sock syndrome, clean the evaporator coil with a non-acid coil cleaner. Cleaning will bring the system back to normal and usually will prevent a complaint for the rest of the season, if this is not the case, and the odor comes back, clean the coil again and apply a coating of Alathene II, a special spray designed to continuously protect coils from fouling caused by air contaminants. The odor is more likely to occur again if you cleaned your coil earlier in the season, especially if the weather conditions force you to change your system back from heating to cooling.
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