We moved into a new home in October 1996. Although it's only our second winter in the house, our heat pump started sporadically giving off an awful odor (my wife likens it to baby puke) at the beginning of this heating season. I later determined the exact situation in which the odor would develop- during the unit's defrost cycle.
Naturally, we tried to work with our builder and the heating and cooling contractor. However, after exploring the obvious possibilities such as a dead "varmint" in the ductwork, both our builder and heating/cooling contractor were out of ideas. I had already started corresponding with the manufacturer by this time.
The result of my research, correspondence with the manufacturer, discussions with the local distributor, and correspondence with a Chattanooga TV station (the station had done a consumerwatch story on the phenomenon in the past) was a diagnosis of Dirty Sock Syndrome or Musty Coil Syndrome. This is apparently caused by a fungus that grows on the heat pumps coils and the smell manifests itself when the unit reverses itself in the defrost cycle. The fungus grows because the coils stay wet with condensation virtually all the time. I've been told by a local distributor that all of the major heat pump manufacturers have had complaints from consumers about this problem. It is apparently more common in relatively humid climates, such as Tennessee's. Although all major manufacturers have apparently had complaints, it does not appear that they've developed a permanent solution to this problem. My research to date indicates that the manufacturers have responded to consumer complaints in varying degrees- some have responded with replacement parts while others have provided replacement equipment free of charge.
Had I known that my heat pump would spew foul odors every defrost cycle, I dare say I would have chosen another heat source.
I am currently working with another heating and cooling contractor to try to correct the problem. This firm has recommended using a bleach and pine sol solution on the unit's coils to try to kill the fungus. I asked if this would do any permanent damage to the coils, and the contractor indicated that it hadn't so far. However, the contractor was noncommittal regarding any future problems. When I indicated to this contractor that I felt this was a manufacturer's defect, he predicted that I would have little success in getting replacement equipment from the manufacturer.
It is interesting to note that the heat pump industry's advertising makes no mention of this maddening "syndrome," although they stress that heat pumps are a clean and efficient source of heat. I would like to encourage any regulatory agencies and or consumer advocates to take a closer look at this phenomenon. If you have also had an experience with Dirty Sock Syndrome, please let me know. I'd like to compare stories and hear what resolution you've had.
Update! Click here for the 4-21-98 update.
Changes last made on: Tues Apr 21 9:00p 1998