We are having a smell come through some of our ducts that kind of smells like cigarette smoke. We've lived in the house for three years and have never had any issues. We did have the air conditioner replaced this summer, but no smells until we turned the furnace on. I did accidentally drop some allergy medicine pills down one of the vents earlier this year.
I've tried to locate any place external to the ducts that the smell could be coming from but haven't been able to find any. Also, it only really comes through on one side of the house. I also had our furnace company out to see if anything was wrong, but they couldn't find anything. I do have a ductwork cleaning scheduled, but am curious to know if there are any thoughts on what it might be. Thanks.