# water closet dfu



## smellslike$tome (Jun 16, 2008)

Another thread got me looking at dfu's vs. pipe diameter. I was all set to blast away at 2.5" pipe serving a wc but woops, it's rated at 4 dfu. I'm looking at the 2009 IPC which I just received the other day and what struck me is the fact that they have a private, 1.6 gpm wc rated at 3 dfu. I never remember wc ever being less than 4 except if included as part of a bathroom group, the bathroom group was rated at 6 dfu. So anyway, if a private, 1.6 gpm wc is rated at 3 dfu then according to the chart (709.2 IPC) "Drainage Fixture Units For Fixture Drains Or Traps", then technically, a wc could be served by a 2" drain which of course is utterly ridiculous. So I started looking for the part that said that this did not apply to wc which required a minimum 3" drain, only I can't find it.

Anybody know where it is or is this just a major flub in the 2009 IPC?


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## plumbpro (Mar 10, 2010)

botom of the chart 710.1(1) note a


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## smellslike$tome (Jun 16, 2008)

I knew it was in there somewhere.

Thanks.

Now, does anybody remember any wc ever being 3 dfu before? Maybe it was before but I sure as heck do not remember it.


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## plumbpro (Mar 10, 2010)

I would have to look around for my old code book, but I think that the 03 IPC was at 4 dfu, the new IPC has it at 3dfu for 1.6gpf/private and 5 dfu for a bathroom group w/ 1.6 private


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## AKdaplumba (Jan 12, 2010)

Doesnt it say a wc has to be min 3"


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## plumbpro (Mar 10, 2010)

yeah, min 3" per the chart I noted in the 2 post up there


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## Tommy plumber (Feb 19, 2010)

*1994 Standard Plumbing Code SBCCI*

My old '94 code book lists DFU for W/C,

Water closet, flushometer tank, public or private 3 DFU
Water closet, private installation 4 DFU
Water closet, public installation 6 DFU


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## a4daddywagon (Sep 11, 2010)

The code also states that waste piping can't be reduced in size from a fixture outlet (even if a smaller pipe meets the DFU rating) as this would cause a high potential for blockage.


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## plumbpro (Mar 10, 2010)

a4daddywagon said:


> The code also states that waste piping can't be reduced in size from a fixture outlet (even if a smaller pipe meets the DFU rating) as this would cause a high potential for blockage.


Except a 3x4 wc 90-this is not considered a reduction in size.


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