randy kline, you should do a peppermint oil test to determine whether or not the odors are coming from a leak in the sewer vent system. If the results of this test verify that the odors are in fact coming from a leak, then fill all of the seldom used plumbing traps with water. If the odors persist, then have a Licensed Master Plumber perform a “Smoke Test” to determine the location of the vent leak, and have it repaired.
If the result of the peppermint oil test proves to be negative, then there is a possibility that microbial growth has occurred in the humidifer of your furnace, and the particular species of microbes growing there produce the odorous gasses. These gasses are then distributed through the heat duct system of your home. JWA