Yesterday, we received a call from a customer and friend complaining that their house smelled like dirty gym socks once they turned on their heat. Their heat was working fine but their house smelled horrible.
This is a result of Dirty Sock Syndrome. Yes, a very strange name. This happens in heat pumps because unlike straight cool heating elements, the heating cycle is not hot enough to kill the bacteria and mold that has grown on the coils since the unit was used last. The temperature is just warm enough to slowly bake off the organic odor and create that horrible dirty sock smell.
What can you do?
Let the system run and run and run. Until it bakes off all that bacteria and mold, you will continue to have the smell. Spraying disinfectant into the return air while the system is running will help. The waiting is the hardest part!