Odor, fan, negative pressure

QUESTION: We are experiencing an unusual odor in our master bathroom when we use
the hall bathroom when the fan is turned on. In other words, when the fan in the hall bath is turned on we seem to get a sewer odor in the bedroom bath. The baths are approximately 30 feet apart. Any ideas?
Boyce Thelen
ANSWER: “A plumbing problem may be causing the smell,” says Vince McDonald of
McDonald Plumbing, Heating and Air Conditioning in Sacramento.
“When the exhaust fan is turned on, it will cause a negative pressure in the home,” he says. “If the house is closed up tightly, the plumbing drain and vent system may become a pathway to bring air into the house, to replace the air that is sucked out by the fan. All plumbing fixtures require a trap to prevent the sewer gasses in the system from entering the home. On the bathroom basin and bathtub the trap is installed directly to the fixture drain built into the toilet. That is why a toilet always holds water,” he says.
“Sometimes you will hear the trap referred to as a “goose neck”. It is configured in such a way that it always holds water and prevents the sewer gas in the drainage system from entering the home. My guess is that you may have a plumbing fixture in the bathroom that is installed without a trap. The trap for the shower and bathtub is found under the house,” McDonald says.
“You may also have a bad toilet seal at the floor or a broken vent pipe in the wall. A licensed plumbing contractor will be able to inspect your plumbing system to make sure it is properly installed and confirm if you indeed have a plumbing problem.”

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