When our whole house a/c unit runs, there is a slight, but bothersome sewer gas smell in the house. We first smelled it only in the upstairs bathroom, but now seem to smell it throughout the house. I suspected it originated in the basement, but when I go down there, I don't seem to smell it. Any suggestions? It has gotten worse as of late. Does this seem like an hvac problem, or a plumbing problem?
Thanks in advance!