# critical distances, UPC

### Users who are viewing this thread

#### 69gtocv

##### New Member
As the title says, looking for info on what is actually measured to determine those. Check out the drawing.

Also, UPC is used where I'm building this house. My drain line to the septic tank from the house is 4". I know my total cross sections of all my vents must equal or exceed that of the 4". From the drawing you can see I'm using 2" for my vent from the lavs, but will increase it to 3" before it exits out the roof to help keep it open in winter conditions. So for my total vent calculations, can I use 3" for that vent or do I have to use 2" since that vent is that size for the majority of its run?

Thanks, Jeff

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• bathroomventsolution3.jpg
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#### NHmaster3015

##### Master Plumber
All distances are critical.

#### Terry

##### The Plumbing Wizard
Staff member
With UPC,

1.5" lines vented within 42"
2" lines vented within 60"
3" lines vented within 72"

#### 69gtocv

##### New Member
With UPC,

1.5" lines vented within 42"
2" lines vented within 60"
3" lines vented within 72"

Thanks, I'm aware of the actual maximum dimensions, my question was whether the lines marked in red in my drawing were where you actually took the measurements from (the horizontal lines only) or do you also have to add the vertical measurement from horizontal until the vent actually takes off from above the double fixture fitting?

And any idea on the 2nd question?

Thanks, Jeff

#### Nukeman

##### Nuclear Engineer
If I'm not mistaken, you will only measure to the wye on the horizontal (where the two lavs tie into the tub line). This is where your wet vent effectively starts.

#### hj

##### Master Plumber
The tub's "critical distance" is from the trap to the point where the sink drain connects, and the toilet's is from the opening to the connection with the sink/tub drain. At those points, the sink's drain becomes the wet vent for those two fixtures.

#### 69gtocv

##### New Member
The tub's "critical distance" is from the trap to the point where the sink drain connects, and the toilet's is from the opening to the connection with the sink/tub drain. At those points, the sink's drain becomes the wet vent for those two fixtures.

Thank you. I was concerned I had to count the distance back to where the vertical comes down as well. I'll be fine now.

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Hey, wait a minute.

This is awkward, but...

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