Sewer Smell When Running Bathroom Fan (2023)

While the principal function of a bathroom fan is to remove hot and moist air from the bathroom, most people agree that removing odors is still a very important secondary function of the exhaust system. So, when you run your bathroom fan, and a few minutes later a sewer smell pervades your bathroom, something must be wrong.

Below I present you with several reasons why running your bathroom fan may be associated with a sewer smell. Perhaps one will stand out as the obvious cause in your situation, but if not, you still have a good place to start. Then, as causes without solutions are only half as helpful, there is a section on how to address each of the potential causes.

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The Smell is Not Coming From Your Fan

Your bathroom exhaust fan is part of your home’s ventilation, not its plumbing, so unless something has gone horribly wrong, it will not be the source of the sewer smell.

Sewer Smell When Running Bathroom Fan (1)
The sewer smell when running the bathroom fan is unlikely to come from the fan itself. Instead, turning on the fan pulls the smell into the bathroom from drains, toilets, and windows due to blockages or incorrect plumbing.

Instead, the smell is most likely coming from some part of your plumbing system.

I won’t go into too much detail on how a bathroom exhaust fan works; all you need to know for addressing a sewer smell issue is that the fan extracts air from the bathroom, creating a negative pressure gradient. This is resolved naturally by the inflowing movement of new air, mostly from outside or other rooms, but in part, it can also pull air from the drains.

While bathroom plumbing is designed to prevent unpleasant odors from creeping their way back into the bathroom air, there are specific circumstances under which the mechanical action of the exhaust fan can pull these odors out of your drains, toilet, or vents.

Possible Causes of a Sewer Smell in the Bathroom

Sewer Smell When Running Bathroom Fan (2)

Blocked Drains

One of the most common reasons for the sewer smell in your bathroom is a build-up of waste and water in the pipes of basins, bathtubs, showers, and toilets.

The predominant reason for this build-up is a combination of dirt, hair, skin flakes, soap, and or waste products that can get cause on the drain stopper or stick together and collect on the inner surfaces of drainpipes.

Moreover, mold can sometimes grow within a drain, and this can also cause or contribute to blockages.

As you can imagine, the longer these materials sit stagnant in a drainpipe, the more likely they are to start rotting, growing bacteria, and stinking!

When you turn your bathroom fan on and the negative pressure system is created, then it can pull some of this foul-smelling air out of your blocked drain and into the general bathroom environment, leading to that distinct sewer smell.

Related Article: 9 Reasons Sinks Drain Slow Even When Not Clogged

(Video) SMELL SEWER GAS don’t call a plumber (EASY FIX)

Airtight Building Construction

Airtightness is a fundamental design feature of homes.

We humans crave control over the temperature, humidity, and airflow rate in our houses so that we can tailor these conditions to our preferences. But airtightness also has very functional purposes, including conservation of energy, preservation of our home’s structural integrity, and promoting the good health of ourselves and our loved ones.

However, if your bathroom is so airtight that when the door is closed, and the fan is running that the major source of “new” air is your drains and toilet, then you could end up pulling sewer-smelling gases into your bathroom.

This can easily be remedied by installing a vent into the bathroom door.

Sewer Smell When Running Bathroom Fan (3)

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Faulty Plumbing Design

Remember when I said that bathroom plumbing is designed to trap unpleasant odors? Well, this only applies to properly plumbed bathrooms.

If your basin, bathtub, shower, or toilet have been improperly plumbed or if there was a fault in one of the plumbing components, then it may mean that these gases can more easily escape or flow the wrong way. Then, when you turn your fan on, it accelerates the upward movement of gases.

(Video) Finding A Sewer Odor In Your Bathroom

This is more likely to be your issue if you also tend to notice a sewer smell after the bathroom door has been closed for a few hours, even if the fan was not running.

Plumbing issues that can cause this include the following:

  • A leak in the water trap of your bathroom fixtures. The water trap is the bent pipe at the fixture-end of the plumbing. An example is the U-shaped pipe you see beneath your bathroom basin. Its function is to hold an amount of water that will block drain gases from coming up through your plughole or toilet bowl. If there is a leak, then the gases are not trapped.
  • Loose pipe connections. If these are not properly secured, then air can escape at these connections and enter the bathroom air.
  • An improperly sealed toilet. If your toilet is not secured to the drainpipe correctly with a well-fitting flange, or if the wax ring has been compromised, it can cause similar problems as a loose pipe connection. You will also likely notice a bit of leaking around your toilet if this is the case.
  • The wrong size plumbing vent. There are plumbing vents in your bathroom that help to keep the pressure in the pipes optimal for function. If these are the wrong size, then the pressure is affected, and the air may not move away from the open part of the fixture as it should.

Improper Positioning of Plumbing Exhaust Vent

Plumbing exhaust vents are required by the International Residential Code (IRC). According to Chapter 31, Section P3102.1 of the IRC:

“The vent system serving each building drain shall have not less than one vent pipe that extends to the outdoors.”

In Section P3103.4 of the IRC, the location of the vent terminal is regulated as follows:

“An open vent terminal from a drainage system shall not be located less than 4 feet (1219 mm) directly beneath any door, openable window or other air intake opening of the building or of an adjacent building, not shall any such vent terminal be within 10 feet (3048 mm) horizontally of such an opening unless it is not less than 3 feet (914 mm) above the top of such an opening.”

If your plumbing exhaust vent has not been located according to code, then when you turn on your bathroom fan, the “fresh” air it is pulling in from outside the bathroom will carry with it a sewer smell.

Neighbor Has a Plumbing Problem

In rare cases, it might actually be your neighbor that has the plumbing issue and not you.

A faulty damper in a multiunit dwelling may result in the sewer smell actually coming through your bathroom fan or being pulled in from other vents in the system while the fan is running.

I have also read about an even rarer (and quite horrifying) case in which a person’s neighbor was the one with the plumbing problem, but the sewer smell pervaded the first person’s bathroom because there was no continuous firewall in their shared bathroom wall! You can read the full thread here.

But before you start panicking, this is a worst-case scenario and is highly unlikely to be the cause of your sewer smell.

Improper Exhaust Fan Venting

If your bathroom exhaust fan vents into the plumbing vent, then this can readily result in a sewer smell whenever you run the bathroom fan. You can read more in my article on the Reasons Why a Bathroom Fan Should Not Be Vented Into a Plumbing Vent.

How Do You Get Rid of Sewer Smells in the Bathroom?

Unclog Bathroom Drains

Sewer Smell When Running Bathroom Fan (5)

As I mentioned previously, a clogged drain is one of the most common issues resulting in a sewer smell when your bathroom fan is running. If you have a clogged drain, then you just need to unclog it!

To a certain extent, this is easier said than done. Some clogs can be cleared by pouring boiling water down the drain a couple of times. Others require chemicals to break down the matter. Still, others will only be dislodged with brute force.

Start with the more common techniques, like boiling water, then move onto the chemicals. However, you have to be so careful that you do not end up mixing the wrong chemicals together and creating a plumbing bomb, which will result in severe damage to your pipes and possibly even personal harm.

If you are unsure or worried, a clogged drain is not something that you have to deal with on your own—call a plumber!

Add an Air Supply Vent

If your problem is airtightness, you can consider opening the window a crack while the fan is running, but this defeats the point of airtightness.

(Video) Sewer Smell In Bathroom? How to Identify and Fix the Problem

As an alternative, you can install an air supply vent, which will pump fresh air into your bathroom so that the fan-induced negative pressure system does not have to pull air from the drains to stabilize.

This video by This Old House provides a great demonstration of how an air supply vent would help you. Although their example involves a range hood in a kitchen, the principle is the same.

Correct the Plumbing Design

If your sewer smell is the result of a plumbing design problem, then you will need to address it according to what the issue is.

A leaking sink trap can be easily replaced as you can see in the below video from The Home Depot.

Loose pipe connections may just need to be tightened (all you would need is a toolbox and some elbow grease).

Replacing your toilet’s flange or wax ring is also something that a committed DIY-er can do, as you can see by the following short instructional video.

If you are hesitant to address the plumbing design issue alone (it does need to be done correctly to prevent further problems and ensure code compliance), then you can hire a professional plumber for the job.

Additionally, if you are uncertain as to what the exact problem is but you have ruled out all the alternatives, then you can also call a plumber out to do an assessment.

Relocate the Plumbing Exhaust Vent

If your plumbing exhaust vent has been installed in the incorrect location, then you will probably need to call a plumber in to do the relocation.

It will involve opening up your bathroom walls to some extent and you also want to make sure that the job is definitely done according to code the second time around!

Inspect the Building Design

If you or your plumber suspect that the problem lies in your neighbor’s bathroom, then you will need to go through the proper channels to get the repairs or alterations attended to.

This is typically a problem with multiunit dwellings, which are managed by a third party (i.e., someone other than you or your neighbor). Ventilation systems in these buildings often fall under common space, so an issue will have to be addressed through the building manager or super.

Correct the Bathroom Fan Venting

Should your problem lie in the fact that your bathroom fan is hooked up to your plumbing vents, it is in your best interests to get the fan re-vented so that the air is exhausted to the outside.

Is Sewage Smell in a Bathroom Dangerous?

The sewage smell in your bathroom is not likely to be extremely or imminently dangerous to your health.

However, the smell is caused by sewer gases and if the problem is severe, then the amount of gas that is in the bathroom air and which you can inhale can reach toxic levels. In other cases, prolonged sewer gas exposure, even for minor leaks, can also lead to adverse health effects.

(Video) Sewer Gas Smell Vent Pipe

If the gases contain hydrogen sulfide, this can turn into a fatal problem!

Furthermore, there are airborne pathogens that can also be released into the bathroom air with the gases, which can lead to other health concerns.

As I said, yours is not likely to be an urgent issue, especially if the smell quickly dissipates once the fan has been turned off. But it is always best and safest practice to address the issue of a sewer smell in your bathroom as soon as possible.


(Video) What to Do If You Smell Sewer Gas

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Why does my bathroom exhaust fan smell like sewage? ›

Improperly Installed or Broken Vent Pipe

There's a vent pipe that airs out your bathroom. If it's installed incorrectly or gets damaged, it can cause a sewage smell in your bathroom. As the pipe is in the wall, you'll need a plumber to remedy this situation.

Why does it smell like sewer when I turn on my bathroom faucet? ›

Your water smells of sewage due to bacteria in your drainpipe producing gases that arise when the faucet is turned on. Hydrogen sulfide is the gas most likely to cause this sewage smell.

Why does my bathroom smell like sewage when I run the washing machine? ›

If your washing machine drain smells like sewage, it may be clogged. A clog in the drain line will create a buildup of organic matter like hair and soap. Bacteria grows on the drain clog, developing an unpleasant sewage-like odor.

How do I stop my bathroom from smelling like sewer? ›

8 Ways to Get Rid of Sewer Gas Smell
  1. Clean the sink overflow. ...
  2. Check the toilet wax ring. ...
  3. Caulk the toilet base. ...
  4. Clean out bacterial growth in drains. ...
  5. Check rarely used bathtubs and sinks. ...
  6. Check for leaks. ...
  7. Inspect your garbage disposal splash guard. ...
  8. Schedule a video drain inspection.

Why does my bathroom smell like sewer at night? ›

One of the most common issues of drain odor is due to blockages and clogs. Any type of blockages, whether they are partial or full, can prevent waste water from properly leaving your home. Over time, this stagnant water sitting in the pipes can build up bacteria and produce pungent odors throughout the night.

Why does my bathroom fan smell like rotten eggs? ›

Leaking Pipes

Mold and mildew growth tends to have a musty smell, while bacteria breaks down the waste escaping from the drain line and can create hydrogen sulfide gas, which smells like rotten eggs.

What does a dry P-trap smell like? ›

Dry air might just be the cause of that unpleasant rotten egg smell in your home. Especially during winter, a P-trap can dry up and allow sewer gas to enter the home.

Why does my water smell like rotten eggs when I turn faucet on? ›

Hydrogen sulfide gas (H2S) can give water a “rotten egg” taste or odor. This gas can occur in wells anywhere and be: Naturally occurring - a result of decay and chemical reactions with soil and rocks. Produced by certain “sulfur bacteria” in the groundwater, well, or plumbing system.

Why does my bathroom smell like septic after showering? ›

Leaky Pipes

Leaky pipes in your bathroom walls or under the shower can allow sewer gases — also known as hydrogen sulfide — to escape, so you may notice the shower drain smells like rotten eggs or sewage.

Can a plumber get rid of sewer smell? ›

Loose connections along the vent pipe or sewer line can also let pungent gases into your home. These will most typically be inside a wall or in the ceiling, so you'll need the help of an experienced plumber to correct this issue.

What neutralizes sewer smell? ›

Before you call a professional, try this DIY method for removing sewer smells. To complete this job you'll need to gather a few supplies: white vinegar, baking soda, bleach, mineral oil, and hot water. Use a sturdy screwdriver to remove the trap of the sewer. Slowly pour one cup of pure white vinegar down the drain.

Is sewer smell in bathroom toxic? ›

The health risks linked to sewer gas exposure include: Hydrogen sulfide poisoning: Hydrogen sulfide smells like rotten eggs, even in low concentrations. Exposure to low levels of hydrogen sulfide can cause eye and respiratory irritation.

Does sewer smell come and go? ›

The smell is likely strongest at floor level or at the drain. While it might come and go (or you may become so used to it that you no longer notice it), it's not fixed even if the smell dissipates for a while.

Why does sewer smell come and go in my house? ›

One of the most common causes of sewage smells is a clogged drain. When your home's wastewater has nowhere to go, the odors will come back up the drain they should be going down.

Why does it smell foul when I go to the bathroom? ›

The most common cause of bathroom smells is mould and mildew that can be caused by a leaking pipe or plumbing fitting. Investigate areas that may be damp from a small water leak or water splashing from the shower or vanity. Common spots include inside or under the vanity cabinet or the wall behind the toilet.

How do I get rid of the smell in my bathroom fan? ›

The primary purpose for having an exhaust fan is to remove the moisture out of the bathroom. These fans help to control and eliminate bathroom odors. Additionally, they add to the safety of the home and its residents by reducing fumes from cleaning agents that could potentially cause health-related issues.

How do you fix a smelly P-trap? ›

To eliminate odors coming from a dry p-trap, pour half a gallon of water into the trap to restore the barrier. It will prevent the odors from seeping through the drain. Another helpful method is to add a cup of white vinegar bleach to get rid of larvae and slow down the evaporation.

Should I clean the P-trap? ›

This pipe is U-shaped, and it helps to collect and drain water. This helps to prevent odors and gasses from coming back up the pipes and into your home. Over time, your P-Trap can start to smell due to build-up and you will need to clean it. Cleaning this pipe will help you to avoid costly repairs in the future.

How do I know if my P-trap is bad? ›

Is your P-trap working properly? If you detect any foul odors near the P-trap that remind you of a smell similar to rotten eggs, then it means that there is hydrogen sulfide present. This, and other harmful gases, bacteria, and viruses, can get into the house if your plumbing trap has malfunctioned.

How do I get the rotten egg smell out of my bathroom sink? ›

To use this strategy, you'll need one cup of baking soda and one cup of white vinegar. Pour the dry baking soda down the drain and then chase it with the vinegar. If you don't have white vinegar on hand, you can use apple cider vinegar or rice vinegar instead.

Should I call a plumber if my water smells like rotten eggs? ›

To get rid of the bad odor, you'll want to contact a plumber to flush and disinfect your tank. Doing so will remove the bacteria and particles that create hydrogen sulfide. During a water heater flush, a plumber can replace your anode rod if it is corroded to prevent the smell in the future.

Why does my house suddenly smell like rotten eggs? ›

The two most common sources for rotten egg smell in the home are electrical components (inside of outlets for example) or a natural gas leak. Natural gas manufacturers are required to add a chemical, called mercaptan, to their gas in order to make it easier to detect a leak.

How do you tell if your sewer vent pipe is clogged? ›

The following are common signs that your sewer vents could be blocked. You may hear gurgling or even see water bubbling up and out of the drains as they drain. You may also hear gurgling coming from your toilet shortly after you flush. The gurgling is caused by air escaping through the drain.

What does a clogged sewer vent smell like? ›

Foul smells that you'd only usually smell from a sewer line can also signal a clogged vent stack. Those are usually caused by toxic sewer gases like ammonia and hydrogen sulfide. The latter, by the way, can make your home smell like rotten eggs. Note that methane is the largest constituent of sewer gases though.

Is there a valve to stop sewer smell? ›

STINK-SHIELD® is an anti-smell valve designed to stop bad smells coming from foul and combined sewage systems.

Will bleach get rid of sewer smell? ›

Pour Some Bleach in It: Bleach, like other disinfectants, kills almost every species of odor-causing bacteria commonly found in drains and sewer lines. So, an easy DIY step to reduce drain odor is to use bleach.

What's the best thing for sewer smell in house? ›

The easiest and most effective way is often a combination of dish soap and hot water, but more stubborn clogs may require you to pull out something like a shop vac or drain snake.

Is it safe to stay in a house with sewage backup? ›

Your health may be impacted if a sewage back-up occurs in your home. Sewage back-ups can contaminate your private drinking well water. It can also pollute surface water (lakes, ponds, rivers, and streams, and reservoirs used for drinking water).

Why does my bathroom sink smell like sewer gas? ›

If the P-trap isn't working properly, sewer gasses can make their way into the bathroom and cause your sink to stink. Your sink should also have a vent that gives backflowing gases somewhere to go. If the sewer smell in your sink is caused by a blocked air vent, you may need professional assistance.

Why does my exhaust smell like sewer? ›

If your exhaust has the distinct noxious smell of rotten eggs, sulfur, or sewer gas, it's likely due to a damaged catalytic converter. When combustion happens in your engine, harmful gases like hydrogen sulfide (which contains sulfur) are created.

How do I get rid of the smell in my exhaust fan? ›

A thorough cleaning will remove the foul smell from the vent.
  1. Remove the screws from the vent filter screen, if applicable. ...
  2. Spray the vent filter with a degreaser. ...
  3. Fill the sink with hot water, and add a teaspoon of liquid dish detergent.
  4. Submerge the filter in water. ...
  5. Rinse the filter with hot water.

Do bathroom fans need to be cleaned? ›

But to function optimally, a bathroom fan must be free of dust and dirt. Generally, it should be cleaned every six months to a year, depending on how much use the bathroom gets and how quickly the cover becomes visibly dirty. (When you see dust gathering on the cover, it's cleaning time.)

How long does it take for a bathroom fan to get rid of smell? ›

Odors, normally whisked away in just a few minutes, may linger for much longer, whether from poop or powerful bathroom cleaning products. But moisture is the real enemy. Humidity from showers fogs up the mirror and leaks into walls. As the warm air cools, it turns into water, and gets trapped in the walls.

What if my exhaust smells like rotten eggs? ›

If your car emits a rotten egg smell, there might be a problem with the catalytic converter, fuel pressure regulator, fuel filter, or even the old transmission fluid. Whatever the cause, if you get the rotten egg smell in your car, take your vehicle to the mechanic as soon as possible and resolve this problem.

What does a backed up sewer smell like? ›

Actually, sewer gas is mostly methane which is odorless but it's almost always mixed with other gases, the most common of which is hydrogen sulfide which has a rotten egg smell.

How often should you clean bathroom fan? ›

It helps get rid of odors, airborne contaminants and moisture in the air. A fan covered in dust doesn't work efficiently, eventually leading to mold, mildew and possibly a house fire. Give it a good cleaning about every six months.

Do bathroom vents remove smell? ›

The primary function of your bathroom exhaust fan is to remove moisture from the air, but it also helps eliminate unpleasant odors from the room. If you've noticed a lingering stench after someone uses the commode, that may indicate the fan is no longer operating efficiently.

Why am I getting sewer smell in my house? ›

Some common causes of sewage smells in households are: A pipe leak: A leaky pipe or drain can cause a buildup of moisture or debris that eventually causes a rotten smell to emanate from the area.

How do I test my house for sewer gas? ›

The first step in getting rid of your sewer gas problem can be easily accomplished by an odor detection test commonly referred to as a “smoke” test. This process involves isolating the sewer system by pushing colored smoke through a roof stack and blocking off the drain line with a test ball.


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