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Sewer Smell When Bathroom Fan Is On [FIXED]

Nobody wants to use their bathroom, flip the exhaust fan on, and be greeted with the stench of sewage.

P-traps installed on your water pipes were created to prevent sewer smells from entering your bathroom. The smell of sewage does not come from your fan, but your bathroom fan can cause sewage gas to rise through air pressure. The problem lies with your p-trap or plumbing. The fan only makes the problem more noticeable.

It’s important that you know the health risks, causes, and solutions for sewage odors spread by your bathroom fan.

These foul odors are not something you should have to put up with. Learn more about this issue so you can fix this problem for good.

bathroom sink p-trap repair

Can Sewer Smell in a Bathroom Make You Sick?

Sewage odors come from sewage gas which can definitely make you sick if exposed to it for a long time.

After all, this gas is a by-product of decaying waste.

These foul odors may turn your stomach and give you headaches and eye or nose irritation in the short term.

But over time, more severe symptoms can develop like memory loss, pink eye, seizures, or even death.

There are also a variety of bacteria and fungi carried by sewage gas that, when breathed in, can result in many different viruses.

These health risks make it all the more vital to diagnose and get rid of any sewage gas entering your bathroom.

Why Is There a Sewer Smell When My Bathroom Fan Is On?


P-traps work by trapping the last bit of water that went down your drain and using that water as a barrier.

This barrier blocks sewage gas, preventing it from getting into your bathroom.

If your shower or sink is not used for a long period of time the water barrier inside the trap can evaporate, allowing sewage gas a way inside your home.

Other times it is not evaporation causing foul sewer odors. Instead, the P-trap is malfunctioning and needs to be replaced.

In either case, having a P-trap that’s not working correctly then allows your bathroom exhaust fan to pick up this sewage gas, making the problem much worse, and making it seem like your fan is to blame.

Powerful Exhaust Fans

Sometimes your fan may be doing its job too well. Extremely powerful bathroom fans can work against you.

Some negative side effects can happen if your bathroom fan has a CFM (Cubic Feet per Minute) rating much higher than your bathroom’s square footage.

For one, the fan may be removing so much moisture that it’s helping the water in the P-trap evaporate more quickly.

But, unfortunately, the fan is then pulling more of this foul air the P-trap was blocking up into your bathroom.

Also, the bathroom fan may be pulling sewage gas caused by other plumbing issues such as loose pipes or improperly sealed toilets.

Improper Venting

Although rare, your bathroom exhaust fan may be vented into your plumbing vent.

This will actually cause the smell of sewage whenever you turn on your bathroom exhaust fan.

This is such a rare cause because no contractor in their right mind would vent a fan into plumbing, and it also violates many building codes and regulations.

More commonly, the vent is routed correctly, but the vent is the wrong size, allowing sewage to creep in.

Due to laziness, recklessness, or a lack of care, there is a slim chance that your ventilation system may be to blame.

Other Plumbing Issues

The P-trap is not the only cause of sewage gas that your bathroom fan tends to pick up.

Other plumbing problems like leaking pipes and unsealed toilets can allow sewage gas passage into your bathroom.

These plumbing issues likely create minor leaks of sewage gas that are not that noticeable until your turn on your bathroom exhaust fan.

All of these plumbing issues not only cause health concerns but can create other issues such as water damage and mold.

How to Get Rid of Sewer Smells in the Bathroom

Fixing a P-Trap

If you have been away from home for a while, your P-trap may only need to be rehydrated, which can easily be done by running your bathtub or shower along with your sink.

In many cases, running your water will be enough for the P-trap to develop its barrier of water and go back to blocking sewage gas.

If that does not work, your P-trap may need to be replaced, which is a job of some difficulty requiring you to remove your drain.

Getting a Less Powerful Fan

Bigger is not always better.

While a bathroom fan should be powerful enough to efficiently do its job, getting a fan with a 100 CFM rating for a 45-square-foot bathroom is overkill.

As a result, a strong fan will bring up sewage gas, helping you realize there is a problem.

If your bathroom is 50 square feet, get a bathroom fan with a CFM rating of 50 or 60, and you will have a less nauseating bathroom experience and a fan that can still efficiently remove moisture.

Inspect Your Venting

Although unlikely, if you think your vents are the cause of your sewage problem, they will need to be inspected first.

If you are experienced with plumbing and ventilation systems, you can do this inspection yourself, saving you some money.

But odds are you will have to hire a professional to inspect your ventilation properly.

The person you hire should also be capable of fixing your ventilation problem if one exists.

Resolve any Issues With Your Plumbing

It’s wise to maintain and inspect your plumbing a few times a year.

Catching leaks before they get worse can save you a lot of money.

Not only can this help with removing foul sewage it can also prevent water damage or mold that come with costly repair bills.

Be diligent and check not just your plumbing but your toilet for a proper seat and seal along with the U-trap underneath your sink.

Repair any issues as you find them.

Adam McCoy

Adam is an HVAC expert and the owner of Mackydo's HVAC Services with decades of experience in fixing and installing air conditioning units, furnaces, and every type of cooling and heating equipment you can think of.

Adam believes that your home is your sanctuary. He loves sharing advice based on his lifelong experience and treats every HVAC problem as if it was his own.

Kyle Tucker

Kyle from Kyle Tucker Plumbing is a certified plumber with over 20 years of professional experience installing plumbing fixtures such as bathtubs, sinks, and toilets, as well as installing gas lines and water pipes, performing bathroom repairs, and more.

Kyle knows how to deal with every plumbing issue that modern homeowners encounter, and he shares his lifelong experience with readers in an engaging and easy-to-digest way.

About Loo Academy

At Loo Academy, our mission is to offer trusted advice for everything related to bathrooms (design ideas, plumbing advice, showering & bathing tips, remodeling guides, and more) — a place where we all spend a great deal of time.

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Published content is regularly fact-checked and revised so that the information we provide is accurate and up-to-date.

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