Plumbing vent distances and code questions and answers.

This article series defines plumbing vent system terms, distances, and functions, and other specifications and code requirements.

Q&A on Plumbing Vent Distances & Codes

These questions and answers about plumbing vent dsistance and codes were posted originally at PLUMBING VENT DISTANCES & ROUTING - home - be sure to check that ARTICLE INDEX and advice.

The basic plumbing vent location relative to a plumbing trap is shown in the sketch at above/left. This sketche is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

[Click to enlarge any image]

On 2022-02-10 by John E Spitzley

I need to move a plumbing vent pipe to install a recessed medicine cabinet - can I just install 90 degree connections to the existing 2-inch piping to move the pipe out of the way? thanks

On 2022-02-12 by Inspectapedia Com Moderator - 90 degree connections okay IF it's a dry vent

@John E Spitzley,

If it's a dry vent - that is it is not used ever for drainage from above - that'd be fine.

On 2021-12-28 by Phil Morin

A laundry room addition was done in the house we're buying. It is about 16 feet to main drain. They've added an AAV at the washer drain. A sink also ties into this line about 12 feet away. Both horizontal. It also has an AAV. Both are 1 1/2".

When washer is draining, it sucks trap in sink dry. I realize both lines are too long, but can't change that. Can I add an AAV somewhere along the drain line to solve this problem? Tying into main vent isn't an option either.

On 2021-12-28 by Inspectapedia Com Moderator - additional AAV may solve problem

@Phil morin,

If you have an adequately-sized AAV at the sink that ought to protect it against siphoning. But sure you can add AAVs.

Read

AIR ADMITTANCE VALVES AAVS

and take a closer look at the AAV sizing table and data given there.

On 2021-11-11 by Leo

If the horizontal spacing distances are met is it OK to extend the roof vent height from 8 “ to approximately 20” to eliminate snow covering the vent here in Alberta?

On 2021-11-11 by Inspectapedia Com Moderator (mod) - extending roof vent height due to snowfall in Alberta

@Leo,

On the above page, you will find this excerpt:

904.1 Roof extension. All open vent pipes that extend through a roof shall be terminated at least [NUMBER - typically 6 ] inches (mm) above the roof, except that where a roof is to be used for any purpose other than weather protection, the vent extensions shall be run at least 7 feet (2134 mm) above the roof.

So extending the vent to 20" is fine as long as it's supported appropriately, especially against wind and your expected snowfall.

Be sure to see

PLUMBING VENT REPAIR

where we show what happens if a vent isn't protected against snow loads.

On 2021-11-05 by Brad

Can I replace pvc pipe vent with a section of marine sanitation hose to get around a post only need about 3 ft. Almost straight up to section that goes thru the roof

On 2021-11-05 by Inspectapedia Com Moderator - can marine sanitation hose replace pvc pipe vent?

@Brad,

If you are not reducing the vent diameter and you are preserving the proper slope throughout it may be perfectly functional. You should check with your local plumbing inspector to make sure they will accept that substitution.

On 2021-10-26 by Nathan

What is the minimum clearance between a vent termination/combustion air intake for a gas furnace, and a sewer line vent? Does this minimum clearance vary depending on what type of termination is used? Is the sewer line vent considered to be a forced air intake or a gravity intake for purposes of gas vent termination clearances?

I am planning to use a low profile termination for the vent on my 80k BTU gas furnace going through the side wall on the fourth story of my home. It would be convenient to use a low profile termination for the sewer line vent through the same sidewall nearby (about 4 feet of horizontal distance and 2 feet of vertical distance, with the sewer vent below the furnace vent).

As I am reading the clearances for a sewer line vent stated in this article, if the sewer vent is within 10 feet horizontally of an air intake (such as the furnace air intake) then it must be two feet above, as per code for sewer lines.

However, as I am reading minimum clearances for gas furnace vent and air intake terminations, described in this article (https://inspectapedia.com/chimneys/Gas-Heater-Direct-Vent-Clearances.php) if the sewer vent is considered a gravity fed air intake, then the gas vent termination must be at least 12 inches away; simple enough.

However if the sewer line is considered a forced air intake (it does suck in air when a toilet is being flushed, etc.) then the furnace vent must be at least three feet above the sewer vent if they are within 10 feet horizontally.

Clearly each cannot be above the other. Is it acceptable to put the sewer vent below the furnace vent if there is some horizontal offset (about 4 feet) but less than 10 feet of total distance between them?

Obviously, odor is not a concern for the combustion air intake (we don't care what the air the furnace is burning smells like).

However, sewer gases can be combustible (can't they?) So, I find it surprising that the plumbing code - the clearances specified by which, I assume are only worried about controlling odor - appears to require a greater clearance than the gas code, which is geared towards, among other things, making sure nothing blows up.

Thanks in advance for your answer. This site is an invaluable resource; keep up the good work.

On 2021-10-26 by inspectapedia.com.moderator - What is the minimum clearance between a vent termination/combustion air intake and a sewer line vent?

@Nathan,

Thank you for an important safety question: clearance distances between direct-vent/combustion air intake openings and sewer line vents.

And thank you for reading carefully and phrasing a most helpful question.

Bottom line: in our OPINION the most-important concern for the case you describe would be an inadequate clearance distance that permitted combustible sewer gases to be drawn into the combustion air intake of a gas-fueled heating appliance - a different problem from the case you described.

Therefore if the sewer vent is within 10 feet horizontally of an air intake (such as at gas-fueled heating appliance combustion air intake) then it must be two feet above, as per code for sewer lines.

You should consider the sewer lin a potential combustible gas outlet, not as an air intake.

Details:

Here are our interpretation and opinion on this question, though we note that your local building code official and your gas heater’s manufacturer are the final legal authority.

1. Rather than treat the sewer line vent as a gravity fed air intake, you should consider the sewer line vent not as an intake but as an outlet - a potential outlet of combustible gases.
   
   For that reason we might prefer to use the clearance distances from a similar combustible gas source (such as a gas meter or gas regulator vent opening) to any heating appliance combustion air intake.
   
   For example, a combustion air intake must be 4 ft. or more from any gas meter - a potential source of combustible gas not unlike sewer gas at a plumbing vent.
   
   So if you meet those more-stringent clearance distances with your own gas furnace combined exhaust/combustion air intake you're likely to be on a safe footing.
2. The sewer vent to air intake that you cite from our PLUMBING VENT DISTANCES & ROUTING article
   
   https://inspectapedia.com/plumbing/Plumbing-Vent-Distance-Codes.php
   
   of 10 ft. horizontally or two feet (or more) vertically might not meet the four-foot distance (in any direction) suggested by point #1 above and so might “meet code” but might be less stringent and in our OPINION less safe than is suggested by the gas meter example.
3. It will be helpful to keep clear in our thinking just what sewer gas concerns we’re seeking to address
   3.a. don’t draw potentially combustible sewer gases (including methane and H2S) into a combustion appliance - fire or explosion safety
   
   3.b. don’t draw smelly or potentially unsanitary sewer gases (same as above + possible pathogens) into a building’s fresh- or ventilation-air supply such as at windows or doors

These are two very different problems and might indeed lead code and standard experts to come up with different clearance distances.

Consider that even if a heater-vent-outlet permitted combustion gases to enter briefly into a sewer or plumbing vent line, that’s not inviting an explosion nor an indoor odors, not is it going to affect the performance of the building drains.

But consider gases flowing in the opposite direction.

If a gas heater’s combustion air inlet were permitted to draw combustible gases (methane and H2S) out of the plumbing or sewer line vent and into the gas appliances’ combustion system we might invite a fire or explosion - clearly unsafe.


For other readers: we discuss these safety concerns and give several tables of clearance distances at

DIRECT VENTS / SIDE WALL VENTS

and at

GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES Separate Table for Direct Vented Gas Appliances - the article you're already reading and to which you have, to our immense gratification, referred.

You won't find an explicit clearance distance between a plumbing vent outlet and a gas appliance exhaust-outlet/combustion-air inlet, but there are comparable clearance distances discussed, such as distances between any exhaust and gravity- or mechanically-induced combustion air inlet openings on a building and any exhaust that might contain combustible gases or contaminants.

Naturally ANY site may contain features that we can't see from our low perch here at InspectApedia and that might change what's needed to be safe.

And also "naturally" you'll want to check the installation instructions for your specific gas heater brand and model or give that company's technical support people a call. Do let us know if you're told something different from what we've suggested here.

On 2021-08-06 by Scott

I have a customer who has an HVAC unit right next to a 2" plumbing pipe which is bringing in the smell from the pipe. What is the proper distance the pipe should be from the unit.

On 2021-08-06 by inspectapedia.com.moderator (mod) - HVAC unit right next to a 2" plumbing pipe

@Scott,

We have a two-part answer:

1. if the pipe violates the unit's required working space clearance distances (as in its installation / operation manual) that's a concern and those distances will e in the manual

2. No plumbing pipe, along its length, would be expected to be an odor source; an HVAC system can't suck sewer gases through the sides or properly-made fittings of any piping material (iron, plastic, copper, cast iron, etc).

But IF there is an opening in plumbing inside a building and near an air handler, such as an open-cleanout access or dry plumbing trap, those defects need to be corrected. That's not a distance issue it's an improper plumbing condition issue.

3. If you are asking about a rooftop plumbing vent too close to a mechanical system air intake, the 10 foot rule probably applies.

If I've misunderstood the question, do help me out here. Perhaps you can post a photo of the situation.

On 2021-07-11 by John GREEN

Question; a neighbor had a rooftop evaporator cooler professionaly installed a few years ago. The DRAIN was routed to the sewer vent pipe just plopped in the top, about a 20 foot run, instead of the gutter or ground. Now isn't that like pipeing in sewer gas to the living area?

They both had a bout with cv19 which is prevelent with waste materials. This seems counter objective to health and safety. Any advice?

On 2021-07-11 by inspectapedia.com.moderator (mod) - proper drainage for rooftop evaporative coolers

@John GREEN,

Thank you for a helpful question on proper drainage for evaporative cooling systems.

We discuss Evaporative Coolers at SWAMP COOLERS

where we include some evaporative cooler installation manuals.

You'll see that the drain piping for evaporative coolers, in the model building codes, is treated the same as air conditioner condensate piping: the same rules apply, including avoiding a connection to sewer piping or vents, probably for the very concern that you raise.

Details are at CONDENSATE DRAINS, CODES
where we include

LOCATIONS for CONDENSATE DISPOSAL - proper locations

PLUMBING CODE for CONDENSATE DRAINS - code citations

Typical IO manual language for evaporative coolers often ducks this problem and will simply refer you to local codes or officials for drain piping rules;

An example manual might state simply

Never drain the cooler onto the roof. Connect a hose from the
drain fitting to a drain or gutter. Water residue could stain the
roof or cause you to slip.

Drain water from the overflow/bleed outlet must be carried away
through a pipe to a suitable discharge point on the building or
property .(According to Local Regulation)

On 2021-07-08 by Blake

Hello.
I'm redoing the plumbing in my disaster/house, and I keep second-guessing myself about venting the bathtub. Can you take a look at this diagram and tell me if this looks up to code?

I basically want to know if I need to add an additional vent arm to the section in red. (The diagram is supposed to be as if you are looking down at the waste pipes from above.)
Thanks in advance for your time and consideration!

On 2021-07-08 by danjoefriedman (mod) - add up DFUs and compare with vent distance and diameter

@Blake,

Thanks for the question and nice sketch.

On the page above you'll see that when the drain is 3" diameter your fixture (tub) can be up to 6 feet from the vent.

In your sketch and GUESSING from your drawing as not all distances are given, your tub is about 70 inches from the "true vent" - or just under 6 ft.

So on that score you're ok.

BUT you need to add up all of the fixtures being vented - converting them into DFUs

(explained at PLUMBING DRAIN FIXTURE UNITS DFUs)

and then check the total DFUs against your vent system.

In sum, when sizing vents we have to consider both distances (fixture to vent) AND total number of fixtures being vented; wyes, bends, etc. add equivalent DFUs to be sure that the vent will work.

On 2021-07-13 by Blake

Thanks so much. I calculated the TOTAL DFUs as 14. I plan to vent the washer and utility sink separately on the opposite end of the house; they will flow into a 3-inch pipe. The kitchen sink will connect to that same 3-inch pipe, and that pipe will then pick up the tub before it hits the combo wye in the diagram.

Plus, the bathroom sink is already vented separately (probably into the attic, but that's another project), so I think I should be good.

On 2021-07-05 by Trevor cook

How close can the vent be to the residential service on the roof?

On 2021-07-05 by inspectapedia.com.moderator (mod)

@Trevor cook,

All of our clearance distances - a huge library - are

at CLEARANCE DISTANCES for BUILDING SYSTEMS & FEATURES

and also therein we see

ELECTRICAL SERVICE WIRE CLEARANCES - clearances to building roof, windows, other features

That's the best guide.

We won't find every possible building detail listed; instead the code inspector would use her judgement.

For example, a plumbing vent that's metal ought to respect the most careful or greatest roof-to-wire distance: you'll see in this Carson Dunlop Assoc. sketch the distance over roof depends on whether the roof is sloped or flat .

On 2021-06-30 by Steve

Can you use 90s in a horizontal plumbing route for a second story bathroom routing around a chimney from a vertical stack

On 2021-06-30 by inspectapedia.com.moderator (mod)

@Steve,

yes but ... be sure to look at pipe diameters an the DFU (Drain Fixture Unit) equivalent totals that you have to add when putting more sanitary (gradual) 90s into a vent system, to be sure that the system diameter and so capacity remain adequate

On 2020-02-18 by Rich

Adding a basement bathroom. The 3 inch mainline under the slab is less than 1 foot from the fixtures. Can I drop each fixtures plumbing line directly to the mainline without the need of additional venting? Of course p traps will be installed on the tub and sink.

The plumbing runs are very short to the mainline and without maneuvering additional pipe to accommodate a vent, would not fit. Do I need to locate a vent on the mainline upstream near the fixtures? Thanks for any advice.

On 2020-02-18 - by (mod) - do I need venting, really?

Rich:

In addition to a P-trap at each fixture, ask your local building inspector if she will accept air-admittance valves, aka vacuum-breaker V-200 type vents that are installed at the fixtures.

See AIR ADMITTANCE VALVES AAVs

On 2019-05-16 by Jane Stewart

The mobile home that I bought, has a big sewer issue. Is it legal to drain all pipes into the toilet? I have a video of running my washing machine & soap is coming out underneath the trailer where the toilet is. Thank you.

On 2019-05-16 - by (mod) -

Jane,

Watch out: Routing plumbing drains to spill into a toilet tank or bowl is not plumbing according to any model plumbing code nor is it a sensible practice.

Worse it suggest such an amateur and in my opinion incompetent approach to building plumbing that I worry what other unsanitary or dangerous work has been done at such a property.

It is also a violation to spill sewage or graywater onto the ground.

On 2019-02-04 by Mark

Do all vents running in the attic have to be three inch

On 2019-02-04 - by (mod) -

Mark

The requirement for 3 in diameter or larger Plumbing vents depends on the plumbing codes that have been adopted where you live a country and city, and also probably the age of the work.

Example it was common in older buildings to use a smaller-diameter vent particularly when the only fixture is being vented where a sink.

...

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

Or see these

Recommended Articles

• PLUMBING DRAIN NOISES where we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises
• PLUMBING VENT DEFECTS & NOISES - home
• PLUMBING VENT CODES, DEFINITIONS, TYPES
• PLUMBING VENT REPAIR

Suggested citation for this web page

PLUMBING VENT DISTANCES & ROUTING FAQS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to PLUMBING SYSTEMS

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