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Odor problem

16 years ago

I also posted on the electrical forum, in case our new fan is the culprit, but would appreciate your ideas, too.

We had a Panasonic exhaust fan installed in the master bathroom of a house that we visit every few months, and at the same time had the existing fans extended to vent out the roof. It was common practice here for builders to just vent into the attic. The electricians had trouble with the new fan, and ended up wiring it to the overhead light switch.

Since then, on two visits I've noticed a slight sewer gas sort of odor in that bathroom. This past weekend, the odor was very strong some times and not at other times. A plumber came today, but couldn't find anything except a need for fresh caulk at the base of 2 toilets. The odor was not apparent then, but it had returned when I checked a couple of hours later.

There appears to be a correlation between running the new exhaust fan and the smell. I left the new fan running to air out the smell of the new caulk, and ended up with a much worse smell, which was near the shower & its fan and not in the water closet. Is it possible to install a bath exhaust fan backwards, so that it blows into the room instead of drawing air out? The ceiling is too high for me to feel the fan with my hand, but a dryer sheet held up to the exhaust fan on a pole was not drawn to it, it only fluttered a little. I'm wondering if the exhaust fan outlet on the roof is near enough to the plumbing vent to draw sewer gas back into the house. Does this seem plausible?

At a previous house, a screw from a vanity light pierced the vent stack behind the sink, and we had a foul odor that came and went. It took the builder months to find the cause of the problem. Today, the plumber went into the attic and said he found no problems there. He thinks a puncture of a vent stack is unlikely, but couldn't say why. He said that odor problems are more likely on rainy or humid days, but today was clear and dry and the odor was just as bad as when it rained earlier.

Thanks for your help.

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