I just bought a house and when we put on the heat for the first time in September, there is a foul odor coming from all of the heat vents in the house. I can't really pinpoint what the odor is, but it seems to be a sewer/rotten egg smell and you can smell it in every room of the house, but it does seem to settle most in one of the hallways. This is also where the return air vents are located. I have had the air ducts cleaned and sanitized and it has not helped. I have had HVAC people out to investigate, but have had no luck. The house was built in 1974 and an addition was put on in 2004. We are on private well and septic and the house has a heat pump and furnace.

Thank you.

If it was only the first time after the system has not been used for awhile, then some odor is normal. All the dust and such that sits all summer long in the heat exchanger gets burned on the first fire up in the fall. Nasty smell at first, but goes away shortly. If it's persistent, then it may be a mold problem in the ductwork or "A" coil. It could also be stagnent water sitting in the A coil drain pan.