Sewage smell in house when house fan is on


Any idea what the problem could be ? Who to call?  Plumber? Thanks. 


Do you have drains in the basement floor?


You may not have enough windows open to let in outside air when the fan is on. Thus it's pulling air from where it can. 

Check and make sure your drain cleanout covers are firmly in place.

Do you have a non functional toilet in the basement or a sink down there you don't use? The trap may have dried out allowing sewer gas into your house exacerbated by the attic fan.  


Dead animal in the chimney?  Had a squirrel die in there years ago and it only started to smell the first day we opened the windows wide.   


Check cap on sewer line in basement.


I think MrIncredible hit it square on the head.


Thanks to all those who responded. We have no drains in the basement floor. There is a wide pipe at a 45 degree angle coming out the floor that gives access to the sewer pipe and the cover is firmly on. 

As for a dead squirrel in the chimney. I don't think so. The chimney is capped and squirrels cannot get in. And we use the fireplace.  

The smell does come from the basement, but also from closets on the second and third floor.  One is adjacent to the bathroom and the other is pretty much on top of it.  

I was thinking that perhaps the waste vent on the roof could be partially blocked.

Any more thoughts ? Thanks  


There is probably a dry trap somewhere. A sink that is never used, for instance. No water in a trap and sewer gases can enter the house. Or maybe a faulty plumbing vent of some sort?


I am concerned.

If there is enough negative pressure when the fan is on to pull sewer gas from a shallow or dry trap, there may be enought negative pressure to pull CarbonMonoxide exhaust from a naturally vented water heater into the living space.


Can you open a couple of windows in the basement while the fan runs and see if the smell fades?


This happens in our house if we don't open enough windows and haven't used our downstairs shower in a while (allowing the trap to dry out.) I just run water in the shower for a bit and open a few more windows and the smell goes away.

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