Re: What's the deal with vent Sizing?
Posted by More on July 04, 19100 at 15:58:01:
In response to Re: What's the deal with vent Sizing?
: I was told that for my vents (stink pipes) that 1 must be 4" all the way through, and the other could be reduced down as far as 1/2 or 2". Right now it looks like have one thats a 3" all the way.. The other one from the basement up to floor level on 2nd floor is a 4". That's as far as I got with the project. Now I have 2 choices: 1) shim the wall out to hide the 4" pipe or 2) reduce down to a 3" which happens to fit perfectly and then at the attic ceiling go back to the 4" up and out. I was told that this is illegal, according to the Rules (code). What is the theory behind this, i.e. Why? I have an old plumbing book (1985) that shows diagrams with 3" pipe all over the place with several fixtures tied in. My house is 111 years old, I really need to use the 3" now, but I don't want to pose a danger to anyone? Is this safe?

The DRAIN waste stack is 4 inch and wants to have a 4 inch vent to prevent turbulent vacuum air creating any suction when the waste is dropped vertically for a long distance. The illegal part is the reduction of wet Waste Drain from a larger to smaller which (when hidden)can cause serious stoppages, clogging and health and sanitation problems. If you need the three inch without shimming out the wall, use it. The other one thats from the basement to the floor that is 4 inch was probably more recently installed, and had a 6 inch plumbing wall into which to put the required 4 inch vent. The waste line is wet and absolutely can't be sized smaller than the largest diameter

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