Small critters are a very real possibility. The house we just bought sat empty for several months, and we are just now getting the mouse problem under control. When one died in the ductwork it was mysterious at first, and worked up to RANK! within a week or so. It was recommended to us by our house inspector that we have the ductwork cleaned, because the PO never used a filter in the furnace (true story!) and there was dog mung everywhere. They found the dead mice, cats took care of the rest.

You should have no smells associated with a new system. The installer should get on top of it before cooling season is over. Mold is a problem when moisture is generated in the cooling mode, not in heating mode. There are several potential causes so there are several possible solutions. The first step is to contact your installer. They should check the drainage. They can install a coated coil if they find no other solution to the problem.

Hi Stefanie, I would be glad to help if I can. I got an air purifier and it seemed like it helped a little as long as it stayed on. We ended up moving our bedroom to the one next to it and turning the musty room into a studio. I took the air purifier out to put into the new bedroom and the stinky room got really bad and thick. I happened to ask my exterminator when he came by for a routine spraying so he checked the attic above the room and said everything was normal critter-wise but theres no fan so it gets very hot. He said he used to do moisture/mold remidiation and would take a look to see if anything explained it. We have a tree with large branches that hover above that room . It looked like rainwater was pooling in the gutter above the window and if you looked under the brick, there was a lot of moss and black staining. He said to trim the branches, treat the black stains, and get a de-humidifier for that room and see what happens. Since taking his advice, I have noticed a big decrease in smell. I am still cautious as to whether this will permanently solve it but its enough of a difference to where the room is bearable to be in now.

Hi, Sonya. I spent a good bit of time on the outside of the home caulking around all entry points, including things like the gas line, the cable TV line, etc. And while we had the wall open, I used some expanding foam to seal around those entry points from the inside. That had been suggested by a home inspector/moisture remediation person that we had out to the house. We live in a wet climate (more than 60 inches of rain per year), and the inspector felt that at times when we were getting a lot of rain, some moisture was entering through those points and probably causing the smell. We have since moved from that house but haven't heard of any issues from the new homeowner, who we still see periodically.