# How do venting tables work?



## AKdaplumba (Jan 12, 2010)

I learned that code in the states are very similar to those in Canada. In our national code book their are venting tables, they give a size, load and how far you can go distance wise. We size by counting everything up and going to the farthest fixture. 

For example, a 4.5 bathroom house, the basement bathroom would be the farthest fixtures from open air. Say you have to go 30m to open air, so 1 1/2 venting colom is no good that you can only go 25m. so you bump up to a 2" vent and go to open air with it.

*its an example, I dont have the code book with me, so the numbers are off*

So my question is do you actually measure how far it is to the farthest fixture then size your vent or do you just say 1-1 1/2 vent and a sewer vent? Split up the bathrooms as you go. We talked about this in school but never seen anything put into practice. I have to say school lacked a fair bit in my opinion, on the other hand I went to night school so it was fast and furious. 

What about townhouses. Do you say 2 bathrooms+kit+landry require one 1 1/2 vent? no calculations involved? When you go into custom homes its not so easy anymore. 

I appreciate your input. 

thanks.


----------



## winslow (Jan 3, 2010)

It all depends on what your local code says, however I'll comment on what the UPC says. You basically have three considerations,

1. The size of the main sewer. The aggregate of the vents through the roof have to be equal or greater than the aggregate of the main sewer. For instance a 4" vent has an aggregate of 12.56. The vents through the roof will have to equal this. 4=12.56 3=7, 2= 3.14, 11/2 =1.75. Therfore you will need either (1) 4", or 4 (2)", or (1) 3 and (2) 2', ect

2. The total lenth of a vent including the maximum distance it can be set horizontally. The maximum of an 11/2 for example is 60ft. The maximum a vent can be set horizontally is 1/3 it's lenth, therefore an 11/2 vent run 60ft can't exceed 20ft horizontally.. A 2" vent can run 120ft, therefore a vent at 120 ft can be set horizontally for 40 ft. If the horizontal distance is beyond this limitation the entire run must be increased 1 pipe size.

3. The fixture load limitations of the vent sizes. An 11/2 vent can handle 8 fixture units, a 2 vent can handle 24 fixture units. Additionally a toilet requires a 2 inch vent.

Hope this helps.


----------



## AKdaplumba (Jan 12, 2010)

so if you were to actually measure, you would only measure the horizontal lengths, not the vertical.

Assuming you have a similar table, are the numbers refering to just the horizontal lengths?


----------



## gladerunner (Jan 24, 2009)

what's an m


----------



## Pipe Rat (Apr 5, 2009)

gladerunner said:


> what's an m


C'mon he's from Canada  they use the Metric system. That would be Meters.:thumbsup:


----------



## Pipe Rat (Apr 5, 2009)

I am a little rusty on this as I haven't done any "inside" plumbing for about seven years. But I would size the vent based on the dfu's and of course keeping in mind the pipesize the vent is serving (around here the minimum size of the vent is 1/2 the diameter of the pipe its serving). Now back to your question, If your vent from the farthest group of fixtures is tying into the vent system and not going to open air you simply calculate the dfu's and developed length to the point you tie into the vent system (not the total distance to open air). Then you recalculate from that tie in point adding all the dfu's below that tie in point to the next tie in or open air.


----------



## AKdaplumba (Jan 12, 2010)

branch vents end at the header just below the roof, it makes no sense to measure every foot to the header, the D. lengths would be way longer then the tables specify. minor vents terminate at either open air or a major vent. 


Glade- Our code book is metric, EVERYTHING ELSE ON SITE INCLUDING PLANS ARE IMPERIAL. What the hell is 1 in 400 for grade? You measure in ft, the book gives meters, its just stupid. its a simple conversion but christ, TIME IS MONEY!!!


----------



## PlungerJockey (Feb 19, 2010)

We don't really do anything big enough to require us to calculate dfu load. Any structure that has a drain is required to have a 3 inch vent. We vent the remaining fixture groups with 1.5 if it's residential and 2 inch if commercial


----------



## AKdaplumba (Jan 12, 2010)

i was hoping that wasnt going to be brought up, sewer vent omits what im asking, but the method I still would like to understand. I want to be good at what I do, not get by...


----------



## Pipe Rat (Apr 5, 2009)

AKdaplumba said:


> i was hoping that wasnt going to be brought up, *sewer vent omits what im asking*, but the method I still would like to understand. I want to be good at what I do, not get by...


???????????? Now you lost me could you rephrase that? You take your farthest fixture group and size it based on developed length to your next tie in then recalculate from that point including addittional dfu's to the next point. Lets look at water line sizing for a minute.... you would calculate your total sfu's for the building (lets leave out friction losses for this example) you would size your piping for the water service accordingly. At each branch you would recalculate the remaining sfu's and downsize accordingly until you get to the last fixture group. Picture this in reverse for the vent system or the same way if you start from the roof penetration.:whistling2:


----------



## AKdaplumba (Jan 12, 2010)

makes sense. thx for the help!


----------

