7 Tips for Troubleshooting Heat Pump Unit Smells

Occasionally a heat pump unit develops a smell problem called "dirty sock syndrome". This is a plague of heat pumps that causes problems for about 1 to 2% of all units. It is a frustrating problem that can be difficult to fix. This syndrome is most common in humid and warm climates. Keep in mind that all heating systems will cause an odor the first time they are used, and often for the next few start-ups also.  

What is 'Dirty Sock Syndrome'?

Most experts agree that dirty sock syndrome is caused by bacteria forming although some people suggest that it is a fungal problem. The microbes grows on the heat pump coils and propagates because the coils are usually wet with condensation. The smell is most noticeable during the defrost cycle.

The small is usually described as a dirty or "locker room" smell, similar to the odor that comes out of a car air conditioner when it has not been used for a while. 

How to Fix

Before you assume the smell is caused by "dirty sock" syndrome, check to see if the odor is present all the time, if it is, it is caused by something else. Dirty sock syndrome only smells when the indoor coil cools and the bacteria releases its smell into the air.

1. There are a number of recommendations for limiting this problem. One of the most common, but short term fixes is to use a bleach and pine solution to the coils to try and kill the bacteria. A tea tree oil solution should also work.

2. If the coil is not the problem, make sure that the problem is not caused by debris and organisms in the drain pan or filter.

3. A thorough cleaning of the coil should bring the system back to normal for the rest of the heating season, but must be redone each summer season, and sometimes more than once.

4. Run the heat pump unit in "Auto" mode which will reduce the humidity in the house, reducing the bacteria build up.

5. If cleaning of the evaporative coil does not work, a coating of Alathene 11 spray might work. This spray protects from airborne contaminates.

6. A newer fix is to attach a UV germicidal light system at the coil and drain pan area. This is said to be a permanent solution. These emitter tubes generally last a little over a year before needing to be replaced.

7. As a last resort, the coil itself may have to be replaced. 

Other Heat Pump Smells

If the smell is more of a burning or electrical burning smell, you should call a professional repair shop to send out a technician. This problem could be weak fan motor or capacitor. The first time you fire-up a heat pump it may give off a slight electrical smell. This is nothing to worry about unless the smell gets worse, or you see smoke. 

Changing the brand of heat pump will not usually fix the smell problem as the problem is often limited to certain households, rather than the unit. It is often related to the living style of those particular households.