Vent connections

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Gregg G

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New construction. Question regarding proper way to tie different vent line sizes together. On one end
of the house is a full bath - tub/shower, toilet, single lavatory. The 2" vent from this bath is routed
horizontally about 40' (straight line with 1/4" / foot grade) and is supported every 48" with J-hooks.
At 40', there is a 1-1/2" vent line from the kitchen sink/dishwasher that needs to tie in with the 2"
bath vent at 90 deg. I know that for drain lines, a sanitary tee is only used for horizontal to vertical
connections - never for horizontal to horizontal.

Is it okay to put a 1-1/2" x 2" x 2" san tee on its side to connect these vents? In my location the
local inspector wants all of the vents to have 1/4" / foot grade, so my thought was to roll the san tee
down a little bit so that the 1-1/2" vent would have the correct grade. Or should I use a 1-1/2" x 2" x 2"
wye fitting instead? It doesn't seem like it would make any difference for "air", and if there was a little
rain that got into the roof vent, wouldn't that moisture travel down a san tee just as easily as a wye?
I need to get "supplies" in the next day or two, so either way is just as easy. Just like to know what is
"correct".

Eventually, the 2" line will merge into a 3" roof vent. I've been told to make sure not to merge too
many DFU into a 2" line, but rather directly into the 3" line. I think the 1-1/2" kitchen sink and
DW vent are okay into the 2" bath vent though.

Kind regards!
Gregg G.
 

Terry

The Plumbing Wizard
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Normally in Washington State, you can get by with two 2" vents and a single 1.5" vent for a three bath home. Those three pipes equal the same area as a 3" pipe.
If the horizontal venting is more than 1/3 of the vertical, the inspector likes to see it bumped up a size.
For venting above the flood levels, you can use a santee anyway you like.
 

Gregg G

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Hi, Terry - Thanks for the definitive answer as always. In retrospect, I could have vented the 2nd bath almost straight up with a 2" vent
through the roof. Then a 1-1/2" vent almost straight up through the roof for the kitchen sink/DW. Then another 2" vent for the Laundry/MB.
We're owner/builders that are kind of slow. When we put on the metal roof I was thinking I wanted to minimize the roof penetrations and
ended up with only a chimney for the wood stove, and (1) 3" DWV vent. I planned to connect the vents in the attic and connect them to
the 3" vent through the roof. I guess that's what I'll continue to do, but it sounds like there is a chance the inspector may want me to bump
up the 2" horizontal runs to 3" if I understand you correctly. Is that per the UPC, or just depends on local inspector? I read through
Chapter 7 of the UPC and saw some tables that I thought made it okay for the 2" horizontal runs. But I can see why it would be better
to minimize horizontal vents and mostly go straight up!

Thanks for your reply!
Gregg G.
 
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