Why is a sewer gas odor coming from the heat vent in the house?

Hi: Believe it or not,, I have actually dealt with situations like this. In most cases the houses have basements or crawl spaces where the heat ducting is located often and the sewage systems in those areas are leaking somewhere and the air ducts are picking it up and displacing its odor into your home. depending on the severity depends on the cure,,,,But remember one thing,,,,, baking soda neutralizes most all sewage smell. Lime will do same. Baking soda is my preferance however. spread out over leakage area and in quantity. Then fix sewage pipe, and seal off your heat vent piping better because it most surely is leaking . Hope this helps: Jimiwane I once had a service call similar to yours. It turned out the air duct to the Master bedroom ran under the shower stall in the Master Bath. The shower drain was leaking waste water onto and into the duct which as you can imaging created a terrible odor.