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.
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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.
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
Open, you can cap that unused vent line, but you also need to clean and sanitize the area where there was a sewage backup.
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
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.
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
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.
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
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.
After flushing basement toilet there is a loud vibration from the vent stack piping. This has been getting worse and at times sounds like a ship horn. The two other toilets upstairs do not have this problem. We have been in the house for ten years and the problem just started in last few months.
Our home is on a septic system but ground gradually drops away ( walk out basement ) so a septic pump was not needed for the basement toilet. There is only one roof vent stack, could there be a partial blockage in the line leading up from the basement toilet? - Frank 7/18/12
Frank I am not sure; I'd start by looking for loose plumbing vent piping.
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
Jackie it sounds as if you need a plumber to check the plumbing vent system for leaks or improper installation
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
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.
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
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.
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
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.
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
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)
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
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.
(Sept 22, 2012) Dennis Knudsen said:
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, 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 buidling 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.
(Sept 30, 2012) Anonymous said:
my hot water
(Oct 13, 2012) Can I clear the waste drain ven said:
I live in a 2 story house with two toilets on the 2nd floor and 1 on the 1st. When not in use all three lose about 2 inches of water but that's it. None were refilling from the tank but I replaced flappers anyway. Could this be related to the waste drain vent? Are all waste drain vents on the roof and is there a way to test and fix this without climbing on the roof? Thanks!
If your traps are siphoning then most likley the venting system is incomplate, missing, inadequate, too distant from drains, or clogged.
(Oct 14, 2012) Robbie said:
Hi I recently installed a new bath room is a largeish house and in doing so the builders took down a stud wall in the middle of the room. Inside the stud wall was the vent pipe for the house w2hich obviously had to be moved. I moved the vent pipe by 2m then iut goes up verticasly for 3 mtrs before entering the loft where it shoot off at a right angle to pick up the old roof vent pipe location.
All seemed fine tilers in and done bathroom in all fine , till this week they call me to say they have a strange smell else where in the house. in a bedroom the smell is very strong of drains when the door is left shut.
This room does have an ensuite etc and a soil pipe in it. though is not the same soil pipe as i worked on. The smell seems to be coming up from the floor in the middle of the room but there is no smell in the ensuite, and no smell on the landing infront of the room etc or the next bedroom.?
Does smell carry that well or is it a case of where its strongest it must be?, im going tomorrow to remove a floorboard or too to inspect further but would love some advise, many thnks
Please see the diagnostic suggestions at SEWER GAS ODORS
(Nov 28, 2012) susan said:
My toilets drain into my drainage hole in my basement floor first before going out to the sewer line? Any ideas why - I have had the lines snaked out but the water is flowing in the wrong direction for the toilets only. Everything else works fine. Anyone have any ideas.
I don't understand the situation from your e-text; perhaps you can send me a sketch or notes by email.
(Dec 6, 2012) Bryan said:
I'm redoing my bathroom on the second floor and moving my toilet. The toilet will be located further down the waste water system (closer to the down drain). Unfortunately, my vent pipe is located about a foot further up the line. Rather than having to move the vent pipe, I was wondering if capping the drain was possible beyond where the toilet will be.
So rather than having the vent pipe connected along the line, the vent pipe would be connected further up the line. The new line would be Capped 3" pipe, vertical vent pipe into 3" drain pipe, toilet into 3" drain pipe, then pipe drains vertically.
Would it be an issue with venting being that the vent is connected about a foot further up the line than where the relocated toilet is? Or does the vent pipe need to be located after the toilet?
I don't have a clear understanding of the situation, why you're capping a drain, and how you're going to vent the toilet; normally just a foot distance change in an existing vent system ought not cause trouble.
(Jan 9, 2013) Nick said:
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.
nly 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.
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.
Jan 17, 2013) Dee said:
Just found out house of 3 years does not have plumbing vent. I am very ill and whole family is thinning hair and skin problems, could this be the cause? Also got mold lab test from bedroom and 'high risk' came back with 8 different kinds of mold, closet houses tub access.
(Apr 2, 2013) Dee said:
I have been hearing a low frequency humming sound in my home for 5 years.I have had contractors,plumbers, pesticide guys out,no one can find the source of this noise. The noise is so bad especially on the second floor of my home.I cannot block out this sound, it even comes through my pillow at night. I cannot get a good night sleep.
When the electric is off the sound is still present. Can it possibly be the roof vents,there are 3 of them and they seem to be in the same location of the sound. The noise sounds like a vibration of some kind, the sound never goes away, but is especially loud at night. Can you please help!
Dee: at the top of any InspectApedia page click on EXPERTS DIRECTORY - you need on-site help with these worries; but first see your doctor.
Easy to test: temporarily block off the vents.
(Feb 5, 2013) Josh said:
Ok, to start off when my sump pump drained my main lines would flood my basement. So I rented an auger and ran the entire line 100 feet, down and did find a couple of clogs. After doing that, the same thing happened when using the washer, then I found a big clog in my shower drain. After unclogging that, the flooding of the main paints got significantly worse and started backing up into my shower and toilets. WHY?
Sounds like an improper type of pump used for sewage ejectrion to a raised main drain, a clog, and perhaps you've pushed clogged material further along the drain;
Ask your plumber to scope the lines with a camera.
(Feb 5, 2014) curt said:
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.
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.
(Feb 7, 2014) Mike said:
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.
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.
(Mar 8, 2014) john foster said:
Could you tell how far a toilet can be installed from the vent stack?
Near the top of this article click on "Click to Show or Hide Related Topics" to see the article index for this topic and you'll see an article title PLUMBING VENT DEFINITIONS, TYPES that includes the specifications you want.
Let us know if anything there is unclear.
(Apr 1, 2014) Question: Can sewer gas smell in condo be from ejector pump in lobby? said:
Hi - I own a garden unit condo that for years has had an intermittent sewer gas smell. The association will not do anything about it, and I'm almost positive that the source of the smell is from the ejector pump, which is located in a closet directly next to the front door of my unit.
An independent plumber told me that the pump was not vented to the outside and the pit may not be sealed. Do you think improper venting/sealing would cause the smell inside my unit? Thanks - Jenny
Yes that sounds possible. It should be easy to demonstrate with a gas detector like the TIF8800 we discus at InspectApedia
(June 17, 2014) tim g said:
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.
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.
(Aug 31, 2014) LynEstr said:
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?
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.
Your venting system sounds improper, unsafe, and illegal - I'd ask for help from a licensed plumber.
(Sept 1, 2014) Anonymous said:
Okay thank you!
(Sept 10, 2014) email@example.com said:
My mother has a moble home trailor kitchen has a double sink vents under sink ran a snake down pipe 45 feet still pluged toilets works tub sink in bathroom also no problem with washing machine stiil pluged can, t craul under trailer no room I know septic needs cleaning do you recormend anything I didn, t check to if theres another vent
If you can't yourself get access to snake a drain line sufficiently it's time to call a professional drain cleaning company who uses a power snake. An experienced operator will also be able to tell you if s/he is encountering collapsed or broken piping and how far out from the snake-in point that is detected
(Sept 23, 2014) Charlie said:
We get a strong foul smell in spots of the house when the washing machine is running and sometimes when running a lot of water in the sink.
A plumber came and ran a rotorooter which alleviated the problem for a few months but it is back and worse. I checked the vent above the washing machine but it is clear and the smell comes in other sides of the house. (We are on a sewer system not septic tank). Could it be a different vent?
The fact that cleaning a drain blockage only temporarily improved the odor problem suggests a recurring blockage.
A blocked vent might cause trap water siphonage that might in turn cause odors at fixtures.
(Sept 25, 2014) Anonymous said:
Thank you. I'll check the vents today.
(Nov 13, 2014) Anonymous said:
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?
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.
(May 2, 2015) Dorothy maynard said:
We have no gas smell from the plumbing vent on the roof , however it is an open pipe on each side of the house .
We live in the carribean and have a. Cement flat rook with a sloap. The roof leaks in theses areas . Is it possible when we have heavy rains the water is leaking through the cement roof from theses pipes?
Thanks for the question. Rainfall in the Caribbean can as you know be intense. If the roof drains are clogged that can increase the chances of leaks into the home. And if the roof drains themselves are damage anywhere in their passage through the building, sure that can send roof drainage into the home.
(July 15, 2015) Big Steve Az said:
Have odor coming through ac ducts,smells like sewer gas.Does not happen all of the time.Please help.
Please see inspectapedia.com/septic/Sewer_Gas_Odors.php for help tracking down and fixing sewer gas odors.
Note that a dead animal in the air handler or ductwork may also smell like sewer gas.
(July 28, 2015) Anita said:
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.
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.
(July 29, 2015) Anita said:
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.
(Sept 11, 2015) Susan said:
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?
Sorry... just posted about a small hole in a basement pipe. It's a vent pipe.
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.
(Oct 20, 2015) sixtuspelesa said:
i want t learn hw t prudece Biogas um from Lesotho so i need any help or advice
Sure - see BIO-FUEL PRODUCTION & USE at inspectApedia.com...
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Or see CLOGGED DRAIN DIAGNOSIS & REPAIR - home
Or see DRAINFIELD FAILURE DIAGNOSIS
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Or see PLUMBING SYSTEM ODORS - home
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