08:21PM | 05/09/05
Member Since: 05/08/05
3 lifetime posts
Hi, I REALLY need advice from experienced people. Recently, there is very bad smell coming from our first floor air return. Although I never really smelled of dead animals, it smells like a dead rat somehow to me. The smell is very strong at about 10:00pm and get milder in the day time. The air retun is in the hall way between the bath room and the living room. The other side of the wall is garage. The smell is also in the garage and the two bed rooms above. I suspect that there is a dead rat, since a couple days before the smell came, we heard rats in the wall and trapped a roof rat. However, I also suspect that there might be some plumbing leakage causing mold or mildew in the duct, since I dont understand that why the smell is strong in the evening. The only reason I have is that my parents in law take shower before bed which is around 9:00pm and their bath room is above the first floor bath room which is near the air return. I have talked to the air duct cleaning people. However before I would spend several hundreds dollars on it, I would like to know whether I should hire a plumber to detect any leakage first. PLEASE, you suggestions and comments are highly appreciated.


08:25PM | 05/11/05
Member Since: 08/29/04
227 lifetime posts
It could be possible that the shower drain is allowing sewer gas to come back into the house and the return air is drawing it back into the heating system. If there is no water in the trap of the shower (or there is no trap) then the sewer gas will be sucked right into the return of the heating system. This can happen if the door is closed and the room draws a vacuum, because of the return air. But most bathrooms don't have return air grills in them, exactly for that reason. In addition return air grills in bathrooms draw in moist air into the duct work, which can develop mold from the dark and moisture. This doesn't sound to me like a properly designed system. I'm wondering who installed it.

Good Luck

Raymond VinZant Plumbing Prof.


12:28PM | 05/24/05
Member Since: 05/08/05
3 lifetime posts
Thank you, Ray, for your reply. The smell is better now. I hired a plumber to check the leak. When he was at my house, it is morning and there is no any smell. He checked the water pressure gauge and there is no movement, so he concluded that there is no leakage and not likely the sewer gas, since he did not smell any. These two days the smell is less stink, but still there around 10:00pm.

BTW, the retun air grill is not in the bath room. There is a air vent in the bath room.

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