Sewer gas smell and solar fan!

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Old 06-26-13, 01:12 PM
B
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Sewer gas smell and solar fan!

Last June I had a solar attic fan installed. the installer put the fan within 18" of the stack. The fan works great and keeps the attic cool. That is until the weather turned cold. I started getting a sewer gas smell out of a shower drain in a second floor bathroom. It happened only intermittently. One cold sunny day it suddenly dawned on me that the smell seemed to happen only on sunny days. If the fan is running full tilt the smell is bad. If its cloudy, but the fan is turning, I get a faint smell. When I get up in the morning and its still dark there's no smell. Or if it s totally cloudy then no smell. I was able to predict exactly when I would get the smell. Since the weather turned warm again there's no smell. I think somehow the fan is pulling/pushing air or messing with the draft of the stack with cold air but not warm air. I questioned the fan installer. He put a 3 foot extension on the stack but that made no difference. Plus he thinks I'm nuts. I had someone run a snake down the stack and there's no obstruction. The fan mfg says to install no closer than 5 feet from to any roof vent. Unfortunately there's no way to turn off the fan so I couldn't test my theory. Does anyone have any thoughts on this?? Thanks
 
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Old 06-26-13, 02:25 PM
B
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Hi Barbara and welcome to the forum.
You said 'I started getting a sewer gas smell out of a shower drain in a second floor bathroom."
That drain is protected from venting sewer gas into your bathroom by a trap filled with water. Is that shower used on a regular basis? If not, then the trap may have dried out.

I will keep pondering this, but I see no connection with properly installed plumbing.

Is it possible the smell is coming from the bath fan and not the shower drain?

Bud
 
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Old 06-26-13, 03:27 PM
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Hi Bud... The shower is used every day. You can smell the odor coming out of the drain. If it is the trap I assumed that the smell would always be there not just when it's cold. There 's two sinks, a tub, and a toilet in the same bathroom with no odors. We did try to check the trap but couldn't get to it since it's above a finished ceiling. Thanks!
 
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Old 06-26-13, 06:11 PM
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I can't figure out how a fan 18" away from your plumbing vent could cause any back-drafting or anything in the vent/drain. If the fan was sucking in smells into the attic, that would be one thing... but smells out of your shower drain sounds odd.

If you look down into the shower drain, you should see some standing water from the trap. That water in the trap should be keeping your sewer gasses out of the bathroom.
 
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Old 06-26-13, 06:52 PM
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I'm concerned that you might have uncovered a bigger problem, a missing trap. If you use that shower the trap should be full and your solar powered attic fan would have no effect.

But, you smell something and only when it is cold outside and the fan is running. Hmmm!

First, an attic exhaust fan does depressurize the attic and due to leakage from house to attic it will pull some air from the house. Now, in your case, if that shower vent is missing, it may also be pulling sewer gas from the shower drain. As for why only cold days may simply relate to the air pressures in a house when it is cold out, they are different than when warm outside. It is a small difference, but apparently enough.

First step is to determine if a functioning trap is down there and I'm not exactly sure how. As Zorfdt said, do you see water in that drain? If you try to run a snake down the shower drain, does go very far and does it come back wet?

Are you on a city sewer or your own septic system?

Bud
 
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Old 06-26-13, 07:10 PM
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I suspect you've got central air and a bathroom fan? If so, the answer is simple.
Gravity. Hot air rises, cool air sinks.

In summer, the air in the bathroom is (generally) cooler that outside - it's a bubble of cool dense air which wants to sink. Basically, inside air wants to stay inside. The attic vent and bathroom fan trying to push air out are somewhat balanced by the tendency of the cooler air in the bathroom to sink and stay in the house.

In contrast, in winter, the air in the bathroom is warmer than outside - it's a bubble of hot air which wants to rise. The attic vent and bathroom fan trying to push air out are supplemented by the tendency of warmer air in the house to rise and push out of the house.
 
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