Plumbing vent piping & system FAQs:

These questions & answers about the building's plumbing vent system piping and connections will help diagnose, find, and cure plumbing system noises, leaks, and odors in buildings including septic or sewage or sewer gas smells or plumbing drain and fixture noises..

This article series describes how to track down and correct these "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well.

What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor.

Causes of gurgling noises at drains, and why some fixtures "gurgle" when a toilet is flushed nearby.

Plumbing Vent Piping Defects May Cause Drain Noises or May Release Dangerous Sewer Gas Odors Indoors

These questions & answers about diagnosing and fixing smells, noises, leaks traced to the plumbing vent system were posted originally

at PLUMBING VENT DEFECTS & NOISES - home - be sure to see those diagnostics. Or some Q&A may also have been posted as comments at the end of this very page.

Open 4-inch vent found in basement, sewage has come out into the house. Can I just cap the vent?

To my horror I discovered an open 4" vent in my basement today, where some waste had poured out. We have an 1885 house and a lot of plumbers here over the years, this may have been hooked up to a commode years ago, who knows?

In any case, if I put a no-hub cap over the open vent should that be ok? - Open 4" vent in cellar 5/15/12

Reply:

Open, you can cap that unused vent line, but you also need to clean and sanitize the area where there was a sewage backup.

 

Infiltrator brand septic system failure report 15 months after new

We've been in our house 5 years, it's got a septic system with those "Infiltrator" brand chambers in the leach field versus stone-and-gravel.

The leach field was brand new when we moved in; 15 mos. later, failed, and the original engineer came out and raked out the lines and installed an air vent in the lawn(he'd never put one in to begin with -who knows why!); and said we were good to go; he said it had not been aerobic from the get-go, hence a biomat buildup in the lines. We're super-careful of water, use Scot tissue brand, HE washing machine, all the right things.

Well lately, maybe past 6 mos., I've noticed in one place (happens to be front or side of house, in front of or to right of vent pipe on top of roof), slight septic smell when something's being used (dishwasher ...toilet got flushed ...shower running - - not just running water in a sink, but those bigger things).

I have really really checked and it's not coming from anywhere inside our house, or near the septic cover in the grass, or in/on the lawn over the leach fields. It's just "in the air" right near the front/side and only when the water's going into the system. It dissipates within minutes after the flow of water into the system is over. Does it sound ominous or within the range of normal? - Margaret 5/9/12

Reply:

Margaret from your note I'm not sure the problem with the system has been correctly diagnosed and repaired.

A lot depends not only on the choice of septic components but how correctly they are installed. But I agree that you should not be smelling sewage. Ask the designer/installer to come by and make a more careful diagnosis and let us know what you're told.

 

Sewer smell in bathroom, plumber warns about drain layout

I have a sewer gas smell in bathroom, coming from around toilet and sink. Plumber said both sink & toilet are sharing a drain pipe & vent pipe. Also the toilet was moved about 8' from vent pipe by previous owners. Does this sound reasonable to you? Had septic tank pumped and it was all good there. The smell is worse on very humid and/or rainy days. - Etha 6/24/12

Reply:

Etha, I think your plumber was warning you that the distance from plumbing fixtures to the vent may be a bit much and may result in inadequate venting.

 

Does it make sense to use a smoke test for plumbing vent leak detection?

We think we have a sewer gas problem in a one story house with one bath, a kitchen, a dishwasher, and a washer. The AC has been running for days due to extreme temperatures, so the house is basically sealed.

The plumber is suggesting a "smoke" test, i.e., toss a couple smoke bombs into the stack and walk around the house to see where the smoke leaks through wall the most. Does this make sense to locate source of sewer gases? - Lillian 7/6/12

Reply: smoke can find some leaks but smoke alone may not be adequate to find all plumbing vent leaks as there is no pressure;

Lillian, I agree with finding the sewer gas leak but the smoke approach is inadequate or incomplete - it won't find a leak inside a wall or ceiling, for example and it can leave debris that clocks a vent line. Don't count on smoke leaking through the wall.

Or if you try this quick and dirty method be prepared to have to look more carefully. I'd spend some effort homing in on where smell is strongest. If necessary to confirm it's the vent system a pressure test could be helpful. Check for the obvious - a loose or leaky toilet seal, a blocked or slow drain, dry plumbing traps etc.

 

Sewer odor seems to come from vents, not the drains

I have a strong sewer smell in my apartment. i cannot detect the smell when sniffing around the fixtures It is the same smell coming from the vents protruding from the apartment. If I leave the door open I can smell it I the hallway of the building. I have flooded water down drains for 10 days. - Jackie 8/20/12

Reply:

Jackie it sounds as if you need a plumber to check the plumbing vent system for leaks or improper installation

 

Smell from plumbing vent encountered when outdoors

The odur problem I am encountering is outdoors and is caused by the vent pipe. If I am outside, and my husband drains his bathwater, an instant odor comes from the pipe on the roof.
I am certain that the smell emitted indeed comes from roof vent.

Awhile back I had roofing done, the roofers got blasted every time the toilet was flushed. I have smelt this odour upon bathtub draining for years...any further comment? - Gail 8/21/12

Reply:

Gail, depending on plumbing vent location above the roof and wind direction and site characteristics, a down draft can on occasion send plumbing vent stack odors down to a yard below. I'd try raising the height of the stack pipe above the roof, or perhaps installing a rotating wind-operated top cap on the vent that does not close the vent off but shelters it from the wind source.

 

Sink, Tub, & Toilet Drains have terrible sewer smell - will pouring water into drains fix this?

We rent a home and it has the terrible sewer smell above the sink, bath tub and toilet in the main floor bathroom.

There are no vents that we can find anywhere. What is there regulations , codes, or laws regarding this?

We have told our landlord many times and they keep sending plumbers with our request but all of them but one would tell us to pour 5 gallons of water down the drains when we smell it. The last plumber said that it was not vented and they would have to vent it. That was 3 weeks ago. I have called the land lord and no word back. - Kathy Tucker 9/15/12

Reply:

Kathy:

pouring water down drains helps re-fill any dry plumbing traps and will reduce odors, but if there are NO plumbing vents in the system, flushing a toilet or emptying a sink or tub can easily siphon water back out of the drain traps and odors will ensue - and may be both unpleasant and UNSAFE.

Plumbing vents are required in a proper and sanitary plumbing system both for function and for safety.

Search InspectAPedia for "Advice for Renters & Tenants" - it's a mold hazard discussion but you'll see our advice for putting health and safety issues in writing to the landlord as well as making immediate oral notification.

 

Strong gas odor comes from toilet when windows are open

We have a strong gas odor coming from our master bath toilet when windows are open in the master bath allowing a cross breeze. The vents are on top of the roof nowhere near windows. The gas is not present with the windows closed. We've replaced the toilet and had 3 different plumbers Reseal the toilet. We still get the gas when windows are open. Any ideas? - Jay 9/11/12

Reply:

Jay, depending on plumbing vent location above the roof, window location and distance below the roof, and wind direction, site characteristics may be giving you a down draft that sends plumbing vent stack odors down into a nearby window.

I'd try raising the height of the stack pipe above the roof, or perhaps installing a rotating wind-operated top cap on the vent that does not close the vent off but shelters it from the wind source.

 

Shower drain gurgles and stinks after flushing the toilet - is this an expensive repair?

We purchased a home about 10 months ago. The master bath shower had a previous leak and we hadn't used it since moving in. A few weeks ago we noticed after flushing the toilet in that bathroom a gurgling sound in the shower along with a stink odor.

What is probably the cause and is this a big cost to fix. We are in the process to start working to figure out the shower leak problem. - Zina 9/08/12

Reply:

Zina,

hearing gurgling in a nearby shower drain when flushing a toilet suggests either a partly blocked drain or a blocked or incomplete plumbing vent. The cost to cure ranges from trivial (unclog a drain using a plunger) to major (replaced a collapsed damaged sewer line or install venting where none was provided)

 

Is it ever ok for a plumbing vent to terminate in an attic?

I inspected a 4 year old home recently. I found what I think were ABS plumbing vents terminated in the attic. I thought they might be for air admittance but they had no valve on them. Is it appropriate to terminate a plumbing vent in the attic? My gut and head both tell me "NO".

Dennis Knudsen - 9/22/12

Reply:

Dennis, I agree completely with your gut and head, as do the model building codes.

Plumbing vents need to be terminated outside the building, usually above the roof line, though there are a few other possibilities - all outdoors.

Terminating a plumbing vent indoors means risk of methane gas accumulation and even a building explosion, as well as less extreme hazards of odors and possible pathogens.

Also, terminating the plumbing vents in the attic provides a source of moisture in an area where it may create mold or other troubles.

In sum, you are quite right. Plumbing vents need to terminate outdoors.

 

ABS plumbing vents terminate in the attic

I inspected a 4 year old home recently. I found what I think were ABS plumbing vents terminated in the attic.

I thought they might be for air admittance but they had no valve on them. Is it appropriate to terminate a plumbing vent in the attic? My gut and head both tell me "NO".

Dennis Knudsen (Sept 22, 2012)

Reply:

Dennis, I agree completely with your gut and head, as do the model building codes. Plumbing vents need to be terminted outside the building, usually above the roof line, though there are a few other possibilites - all outdoors.

Terminating a plumbing vent indoors means risk of methane gas accumulation and even a building explosion, as well as less extreme hazards of odors and possible pathogens. Also, terminating the plumbing vents in the attic provides a source of moisture in an area where it may create mold or other troubles.

In sum, you are right. Plumbing vents need to terminate outdoors.

(Sept 25, 2012) Dennis Knudsen said:
Thanks, Dan. You reinforced my conclusion.

 

In winter we hear a dripping noise in the wall near a plumbing vent

During the winter when we run the hot water in kitchen or mainly the dishwasher(First Floor). We have water that is dripping in the (Second Floor) wallspace near the vent area. No plumbing is in the area. Water stains are visable on tne outdoor siding.

It only happens during the winter as we believe that it is condensation that is leaking from a broken vent pipe. Is my only recourse to remove the siding to find the trouble ? No stains inside or smells. (Jan 9, 2013) Nick

Reply:

I suspect as do you that moisture in the vent line is freezing, then later melting and dripping out through a leaky or broken vent line as you say. I'd remove materials to look wherever repair will be easiest: drywall repairs may be easier than chopping open the building from outside.

What's causing a constant clicking in our plumbing vent pipe

We have constant 'clicking' in our plumbing vent pipe - just beside our bedroom. We have cut the wall twice to discover the problem but haven't had any luck. What can we do to stop this - we don't sleep while this is going on and it takes a while for the vent to cool down after using the hot water. Help. (July 28, 2015) Anita

Reply:

Check the clearance space around the vent pipe - assuming this is a metal pipe that is expanding or contracting it may be rubbing on building components that it is touching. Don't just cut out larger openings around pipes to give open cleaerance.

Clearance openings may need to be sealed with a fire rated caulk or foam to prevent fire or smoke spread in event of a fire and to comply with your local codes. Check that with your building department.

Also see

POPPING SNAPPING NOISE DIAGNOSIS

Anita

Thanks for your answer. The vent pipe is some type of black 'plastic' - and we only cut out the drywall to see if we could ascertain the problem. I am wondering if the builder used the cheapest kind of vent pipe and if a better quality would not give us the same problem.
Thanks for your consideration.

 

Recent water on basement floor traced to a main drain vent

I've lived in the same house since 1978 and never had this issue. I started to notice water on the basement floor and believe I've traced the cause to the vent which goes from the main drain, up through the wall and exiting through the roof. Since we've had a lot of snow in Mi.

this winter I thought maybe my roof vents were covered with snow, but when I got up on the roof they were all poking through the snow.

I shoveled the snow from around the vent and inspected area but found no cracks or other problem. There was 4-5 inches of ice along that eve. My bathroom fan vent is also in that same area. there was no ice buildup around either vent. (Feb 5, 2014) curt

Reply:

It's possible that moisture condensed, froze, then melted and ran back through the building; if those freezing conditions didn't occur before, a leak in the vent piping might not have been noticed.

In a properly installed plumbing vent, moisture condensing (or ice melting) inside the vent piping should drain back to the drain piping portion of the system - without leaking out.

Water on the basement floor can be tricky to diagnose - we'd like to follow the water backwards towards its source. But if time has elapsed between a leak event and the time the water is noticed, the back-path may have dried, making for a bit more difficult detective work.

Follow the water, or water stains.

 

What causes sewer gas odors when septic system is overloaded?

We have a sewer gas odor when too much water is drained into the septic at one time. We also have the odor when the wind is blowing from a certain direction.

This usually happens in the cold weather months. In the summer we don't seem to be bothered with this as much. Our house windows are open in the summer though. Have been dealing with this problem for 30 yrs and no one seems to have a clue. (Feb 7, 2014) Mike

Reply:

Mike,

Septic tank pump-out should not cause a sewer gas odor except perhaps immediately during the pumping operation as the tank is open and truck is pumping; The next time the tank is pumped I'd take a look closely at what's going on at the tank, including back-flow into the tank from the drainfield - which would suggest a failed field.

A sketch with distances tank to house might be helpful.

 

Can I vent the bathroom exhaust fan into the plumbing vent stack?

Can a bathroom vent fan be vented into the plumbing vent stack? it is a commercial block building and it is some distance to the nearest exterior wall. (June 17, 2014) tim g

Reply: no

Nowhere have I found that approach approved. It's a dangerous idea that wouldn't vent successfully (the vent stack is too-small in diameter for a building vent). The danger is back-pressure in the vent system followed by explosive methane gas leaks into a building.

Is it Ever OK to cover a plumbing vent pipe that's being used to vent an exhaust fan?

I recently moved in to a rehabbed home. I noticed that my bathroom has 2 PVC pipes coming out of the room. One of them I know for sure is connected to the exhaust fan.

The other one I do now know what it is for and I don't know if it was used for the old exhaust. I recently discovered leaking in the back of my tub where the pipes are and its actually coming from the 2nd PVC pipe.

My husband got on the room and put a measuring tape in the PVC and I was able to see it behind the tub. I would like to know if it is okay to cover this PVC pipe with a pvc cap or just put a pvc vent cap? (Aug 31, 2014) LynEstr

Reply: your plumbing and vcenting systems are improper and unsafe

Lyn

Because some PVC pipes are used to vent combustion gases, it could be dangerous, even fatal to cover a PVC or other exhaust before you know absolutely for certain that it is not in use.

Watch out: Your venting system sounds improper, unsafe, and illegal - I'd ask for help from a licensed plumber.

 

Does it work to add a filter on a plumbing vent to address odors?

Our log home has 3 baths, two on the main level and one on the lower level. Our septic odor is only in one of the two baths on the main level.

I see one stack/vent in that general area, so does that mean all three baths are connected to the same vent? A friend said today our problem may be inversion and the solution is to install a charcoal filter in the vent. Make sense? (Nov 13, 2014) Anonymous

Reply: better to fix the problem than to treat the symptom

I'm not an enthusiast of adding vent filters - sources of freezing, clogging, vent blockage, and falls off roofs; and I prefer to focus on finding and fixing the actual problem. I suspect that if the problem were downdrafts that push sewer gases down from their vent point on the roof then you ought to smell odors outside and everywhere around the house.

I'd first check the building plans, visible piping &c to see if we can determine where plumbing vents run.

I'd also look at the odor history - if it's recent one suspects a blockage or a new leak while if it's since time of construction one suspects improper vent piping.

 

Is it OK to patch a vent pipe hole with epoxy?

There is a small hole in a 1.5 inch cast iron drain pipe in my basement. What is the proper way to seal a hole? Would it be sufficient to caulk it or epoxy it?

It's a vent pipe. (Sept 11, 2015) Susan

Reply: yes, with this warning

You can make a patch using a clamp-on device or clean and epoxy the opening; beware that often the pipe around the visible opening will be corroded and fragile.

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Continue reading at PLUMBING VENT DEFECTS & NOISES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see PLUMBING VENT ODOR FAQs-2 - more diagnostic questions & answers on plumbing vent problems traced to slow drains, noises, odors.

Or see these

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