# Combination waste and vent



## Plumbus

For those of you do restaurants, commercial kitchens or supermarkets where there are multiple floor sinks and floor drains, do you ever install your waste using a combination and waste and vent layout?
I'm amazed that even on engineered projects they don't avail themselves of the option of using a code compliant combination waste and vent design.
Fortunately, most AHJ's in my area are open to such systems without requiring wet stamped drawings (as long as they are installed in a fashion that follows the language of the code).


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## justme

Yes , here in Texas we have the UPC and IPC so we install the CWV under the UPC and the CDV under the IPC. The city of Dallas even lets you install the CDV on grease waste when just about all other jurisdictions don't allow that. Definitely makes the topout go much quicker.


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## ShtRnsdownhill

Plumbus said:


> For those of you do restaurants, commercial kitchens or supermarkets where there are multiple floor sinks and floor drains, do you ever install your waste using a combination and waste and vent layout?
> I'm amazed that even on engineered projects they don't avail themselves of the option of using a code compliant combination waste and vent design.
> Fortunately, most AHJ's in my area are open to such systems without requiring wet stamped drawings (as long as they are installed in a fashion that follows the language of the code).


probably because those engineers have no clue what wet venting is, but if they worked in the field they might pick up some knowledge...:yes:


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## bct p&h

ShtRnsdownhill said:


> probably because those engineers have no clue what wet venting is, but if they worked in the field they might pick up some knowledge...:yes:


A combination waste and vent system is completely different than wet venting.
Combination waste and vent is over sizing the line up to the trap. Let's say it's a 2" trap, you would run a 3" line up to it. Theory is that the 2" trap will never allow enough water through it to fill the 3" line. The top of the 3" would act as a vent because it would never be full of water.
Wet venting still has a traditional vent going going up but you can run horizontal below the flood level because there is a sink washing it down.
Obviously there's more to it than my over simplified explanation but there are differences between wet venting and combination waste and vent systems.


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## ShtRnsdownhill

bct p&h said:


> A combination waste and vent system is completely different than wet venting.
> Combination waste and vent is over sizing the line up to the trap. Let's say it's a 2" trap, you would run a 3" line up to it. Theory is that the 2" trap will never allow enough water through it to fill the 3" line. The top of the 3" would act as a vent because it would never be full of water.
> Wet venting still has a traditional vent going going up but you can run horizontal below the flood level because there is a sink washing it down.
> Obviously there's more to it than my over simplified explanation but there are differences between wet venting and combination waste and vent systems.


Ah, gotcha..I would think the cost of the oversize piping and fittings it would be close to just venting or use a few common vents..the problem I see with that especially on mop and floor drains is all the junk that would go down would fill half the pipe solid and then you loose the vent..good in theory not in application..


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## plumbbama

this is wet venting


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## ShtRnsdownhill

plumbbama said:


> this is wet venting


that aint jack without an into and a disgrace of a name.


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## Plumber

They're called combi wv, btw.


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## rjbphd

plumbbama said:


> this is wet venting


Not a plumber here..


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## justme

ShtRnsdownhill said:


> Ah, gotcha..I would think the cost of the oversize piping and fittings it would be close to just venting or use a few common vents..the problem I see with that especially on mop and floor drains is all the junk that would go down would fill half the pipe solid and then you loose the vent..good in theory not in application..



HMMMMMMM, well the savings is in the fact you don't have to run a vent on every fixture so you save tons of money on the topout not mention in the rough.


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## ShtRnsdownhill

justme said:


> HMMMMMMM, well the savings is in the fact you don't have to run a vent on every fixture so you save tons of money on the topout not mention in the rough.


If you use wet venting you wont have the chance of loosing your vent when the pipes fill up with sand and grease, that all the drain cleaners know will happen with floor drains and mop sinks...and you will save running a vent for every fixture..


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## bdaltonph

I used a combination waste and vent system in a salon once for the hairs sinks. The sinks (4 of them) were on stands or stations away from the walls making conventional venting nearly impossible. It worked out pretty good. 

Your post makes me think of a continuing ed instructor I had. He would always say the same thing. Couldn't understand why more guys didn't use them. Thing is here nj on commercial work we have to follow the engineer plan. Which are generally way over vented.


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## 89plumbum

We try to circuit vent everything. It's a huge money saver. IMO, its a great working system.


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## Plumbus

Nice description by BTC P&H. Combination waste and vent systems are a good alternative when faced with lots of floor drains and floor sinks, especially when they are way out in the middle of nowhere. For example, in a commercial kitchen with 10 such fixtures, the extra cost due to over sizing the drain lines is more than compensated by the material and labor saved by the elimination, depending on distance from the main line, of as many as 9 vents.


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## justme

ShtRnsdownhill said:


> If you use wet venting you wont have the chance of loosing your vent when the pipes fill up with sand and grease, that all the drain cleaners know will happen with floor drains and mop sinks...and you will save running a vent for every fixture..


That's what my jetter is for, get them coming and going.


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## Michaelcookplum

We do combo waste vent on commercial groundworks, works just fine. What doesn't make sense to me is why most people including myself, stub 2" up through kitchen sink and island sink and still put a tee and studor vent under cabinet. Could just put a 2" 90 and trap. 


Sent from my iPhone using Tapatalk


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## john0305

*multiple fixtures in comb waste/vent system?*



bct p&h said:


> A combination waste and vent system is completely different than wet venting.
> Combination waste and vent is over sizing the line up to the trap. Let's say it's a 2" trap, you would run a 3" line up to it. Theory is that the 2" trap will never allow enough water through it to fill the 3" line. The top of the 3" would act as a vent because it would never be full of water.
> Wet venting still has a traditional vent going going up but you can run horizontal below the flood level because there is a sink washing it down.
> Obviously there's more to it than my over simplified explanation but there are differences between wet venting and combination waste and vent systems.


Is it alright to tie multiple fixtures into a comb waste & vent system? I have a project to install floor drains in an existing storefront for display freezers/coolers. The customer doesn't want exposed pipe in the retail space so if I could run 5 floor drains, with a combined dfu of 2.5 (IPC 709.4.1) into a 2" combination waste/vent this would solve all requirements. Thanks


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## Tommy plumber

This forum is for plumbing professionals only. Do-it-yourselfers are not permitted to join. The forum does not condone or encourage anyone who isn't properly trained in the plumbing trade to attempt to repair, alter, extend, design or install any plumbing, gas, vent, sewer, medical gas, drain, septic, water line, or any other plumbing systems. Thank you.


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## plumb1801

Depending on the layout of the building we will usually use either CWV or circuit venting system both will provide adequate venting if sized properly. I like to use a circuit vent for commercial laundry facilities where the machines are located in the middle of the shop seams to work out the best. I just bid a Italian restaurant which has 6 floor sinks and 2 floor drains on 1 branch line. The engineer didn't do an isometric drawing for the waste and vent system on this project so I designed a circuit vent. The walls laid out in a way where I was able to get my vents up and tied back together- not typical. In my area an isometric drawing is required for all plumbing systems commercial or residential. If none is provided by an engineer then the plumber is responsible once approved some inspectors will use that as there code book instead of really knowing the code.


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## ironandfire

Plumbus said:


> For those of you do restaurants, commercial kitchens or supermarkets where there are multiple floor sinks and floor drains, do you ever install your waste using a combination and waste and vent layout?
> I'm amazed that even on engineered projects they don't avail themselves of the option of using a code compliant combination waste and vent design.
> Fortunately, most AHJ's in my area are open to such systems without requiring wet stamped drawings (as long as they are installed in a fashion that follows the language of the code).


 Yes ! It's always bugged me that nobody has a clear understanding of how to interpret a set of plans. My thought is that plans are theory and not gospel . Some guys seem to see it the other way around. I don't know how many times I've heard " Put it in just like it shows". 
Case in point. Combination waste and vent for a sink. You'll never see that on a set of plans.


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## ShtRnsdownhill

ironandfire said:


> Yes ! It's always bugged me that nobody has a clear understanding of how to interpret a set of plans. My thought is that plans are theory and not gospel . Some guys seem to see it the other way around. I don't know how many times I've heard " Put it in just like it shows".
> Case in point. Combination waste and vent for a sink. You'll never see that on a set of plans.


 most plumbing plans are NOT drawn up by a licensed plumber but some hack engineer or architect that just goes with a cad program, I have seen many times they spec for an 1 1/4 inch vent..WTF there are no DWV pipes that are 1 1/4 inch unless you go with copper and thats not code... 

usually for commercial you follow where the pipes go because other trades have their specified spot to run their utilities so everything fits where it should...or thats the plan....


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## ironandfire

A combination waste and vent is too specialized for the engineer to illustrate even though it's an engineered venting system. Too much detail for a set of plans. I would assume they're just illustrating a simple theory that a fixture needs to be vented.
Specs on the other hand offer a level of detail the plans don't. And never really are specific on venting options (which should give me, as a professional, the option to do whatever).


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## ironandfire

The owner has a specific request; "No 3/8" rod". 
O.k. , I'd be more than happy to your drinking fountain supply with that material.


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## Tommy plumber

I did a re-model years ago on a condo. The condo was up on the 12th floor. The owner moved some fixtures around in addition to replacing fixtures.

When I was working on the kitchen sink, I noticed that the cast iron stack was 5". That was new to me. That 5" stack was both the vent & drain for the condo kitchen sink. 

With other commercial jobs that I was on, there were {2} separate lines for the fixtures. One was a dedicated vent that went up through the roof, and the other line was a dedicated drain line. A perfect example is carrier systems. 

But with the condo re-model that I mentioned earlier, the only line for both the vent and the waste was this vertical 5" cast iron. That is a combination waste & vent. The plumbing code requires a few things, like the stack cant reduce in size; it has to remain the same size all the way up through the roof, no water closets can dump into it {neither can urinals}, it can't offset, and it has to be over-sized. Over-sized in the sense that if you add up the DFU's for the stack, the code would allow maybe a 3" vertical stack, but since this will be a combination waste & vent, the code requires the vertical stack to be 5".

It's been a while since I've done anything commercial, now a days I just do small residential stuff.

I am checking my code book and what I am describing is called "Waste stack vent" in my code. Section 910.

I know it as a combination waste & vent. I forgot that offsets are allowed but only above the last fixture. That is called the stack vent. That section can have offsets, but has to be the same size as the entire stack's diameter.

Any of you guys who do a lot of commercial, feel free to jump in.


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## ironandfire

In Pennsylvania, I think they call that a Philly single stack. Don't know if Pa. is I. P. C.


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## Toli

Tommy plumber said:


> I did a re-model years ago on a condo. The condo was up on the 12th floor. The owner moved some fixtures around in addition to replacing fixtures.
> 
> When I was working on the kitchen sink, I noticed that the cast iron stack was 5". That was new to me. That 5" stack was both the vent & drain for the condo kitchen sink.
> 
> With other commercial jobs that I was on, there were {2} separate lines for the fixtures. One was a dedicated vent that went up through the roof, and the other line was a dedicated drain line. A perfect example is carrier systems.
> 
> But with the condo re-model that I mentioned earlier, the only line for both the vent and the waste was this vertical 5" cast iron. That is a combination waste & vent. The plumbing code requires a few things, like the stack cant reduce in size; it has to remain the same size all the way up through the roof, no water closets can dump into it {neither can urinals}, it can't offset, and it has to be over-sized. Over-sized in the sense that if you add up the DFU's for the stack, the code would allow maybe a 3" vertical stack, but since this will be a combination waste & vent, the code requires the vertical stack to be 5".
> 
> It's been a while since I've done anything commercial, now a days I just do small residential stuff.
> 
> I am checking my code book and what I am describing is called "Waste stack vent" in my code. Section 910.
> 
> I know it as a combination waste & vent. I forgot that offsets are allowed but only above the last fixture. That is called the stack vent. That section can have offsets, but has to be the same size as the entire stack's diameter.
> 
> Any of you guys who do a lot of commercial, feel free to jump in.



That might have been a sovent system. 

I’ll admit I don’t know all the codes around the country, but I don’t think a combo waste/vent can be used on multiple levels.


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## jakewilcox

To use a combo wv system (around here anyway) the pipe usually has be over sized (I don't remember right now how much per fixture unit; I'm not going to look it up right now) and graded as per the spec of the size in the code book. Its been a few years. My old company liked to use them on floor drains and floor sinks, in particular floor sinks in the middle of a grocery store for condensate drains for the freezers and refrigerators because there is a lot of distance to run a vent for a floor sink between a floor sink in the middle of a store and the wall. 

They work fine, but they are almost ALWAYS a fight with the inspector.


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