DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   Plumbing Forum (
-   -   PVC vent (

joshuajvd 03-25-2010 08:31 AM

PVC vent
I opened up the closet wall on our top floor to extend the closet and I found a black 3" PVC pipe extending from floor to ceiling and through the attic into the roof line. I am assuming this is a vent, but I am not sure for what. I am thinking either the hot water heater or the basement suite bathroom fan, but neither of these make sense to me as it would have been the hardest and longest way to vent it. Also, coming up beside it are 2 water pipes, the kind that typically carry hot and cold water. I am confused as to why those are there if the PVC is in fact a vent.

oldognewtrick 03-25-2010 09:30 AM

Joshua, welcome to HRT. The pipe you are seeing is probably a vent pipe for the sewer drain. This allows air to enter the drain, if you didn't have this pipe it would cause a vacuum and the water wouldn't drain fast. Try turning a 2liter bottle upside down and see how it drains. Punch a hole it the bottom, turn it over and it will flow much faster.

joshuajvd 03-25-2010 09:54 AM

Awesome, thanks, I guess there is no easy way of moving that then.

Nestor_Kelebay 03-25-2010 03:37 PM

Better to make do with a smaller closet than start modifying your vent stack.

I'm not a plumber so I don't know if there's any requirement that the vent stack needs to be straight. But, if I had to guess, I'd guess that the plumbing code requires it to be straight and vertical so there's negligible chance it could get blocked with twigs and leaves and stuff that might fall into it. If the vent stack is straight and vertical, then anything that falls in would fall to the bottom and be washed away every time you flush your toilet. But, I don't know for sure that there's any requirement that the vent stack be straight.

Here's how it works:

That 3 inch PVC pipe goes from just below your basement concrete floor to just above your roof line where it's open to the atmosphere. All the drains in your house try to empty into the lower part of that pipe (called the "soil stack") and all the vent piping in your house try to connect to the upper part of that same pipe (called the "vent stack) before it goes through the roof in order to reduce the number of roof penetrations and therefore potential leakage sites. It's the same pipe, but the lower part is often called the "soil stack" whereas the upper part is called the "vent stack", and the whole thing together is commonly referred to as the "vent stack".

Once the soil stack goes into your basement floor, it turns and runs at a shallow downward angle to the sewer pipe buried under the middle of the street your house is on. That shallow sloping pipe is the main drain line from your house. Typically, the first 10 to 20 feet of the main drain line will be where solids (mostly from your kitchen sink) will accumulate. Consequently, if you look on your basement floor near where the soil stack goes into the concrete, you will find a "clean out". That's where a plumber will run his snake in to clear the main drain line. It's good preventative maintenance to have the main drain line from your house cleared every 10 years or so just to avoid drain problems which are often the result of a partially clogged main drain line.

Where I live, the building code requires that there also be a cleanout at every change in direction of the main drain line under the basement floor, too. That way, if push comes to shove, a plumber can clear each straight section of the main drain line separately. So, if you're doing any home renovations, then keep in mind that you need to provide access to these clean outs, and so you don't want to install flooring over them to make them inaccessible and hide their location.

inspectorD 03-25-2010 04:15 PM

Nice photo Nestor, that helps folks alot.
Just one minor issue with this that I found ...your lingo is off.
Black pipe is ABS...white pipe is PVC, do not mix the two if you can help it, they do not glue together nicely.
Just so you know for when you talk to the local supply house.
Good luck.:)

Nestor_Kelebay 03-25-2010 07:25 PM

Yeah, that one slipped right by me. I didn't even notice that he said the pipe was both black and PVC.

Did you know that ABS pipe cement is really nothing more than some ABS plastic dissolved in acetone, methyl ethyl ketone or a mixture of the two?

The MSDS for Genova's ABS Low-VOC solvent cement gives it's composition as:

Acetone: 10 to 30 percent
Methyl Ethyl Ketone: 50 to 75 percent
ABS resin: 18 to 40 percent
The reason why this would be considered a Low-VOC product is ONLY because acetone isn't considered a Volatile Organic Compound according to the US government.

The MSDS for Oatey Black ABS Cement reads as follows:
Methyl Ethyl Ketone: 55 to 75 percent
ABS Resin: 25 to 40 percent
Black colourant: 0 to 5 percent (this is just black pigment, which is ordinary soot)

Methyl Ethyl Ketone and acetone are chemical cousins.

Anything with the general formula:


is called a "ketone". The carbon atom double bonded to an oxygen atom in the middle is called a "carbonyl group" (C=O).

If both A and B are methyl groups (-CH3) then it's the simplest ketone, called "dimethyl ketone", or "acetone" for short.

If A is a methyl group (-CH3) and B is an ethyl group (-CH2-CH3), then it's called "methyl ethyl ketone, or "MEK" for short.

That means that if your ABS cement is getting thick, all you need to do to restore it to brand new is to pour in some methyl ethyl ketone, which you can buy at most paint stores. Acetone evaporates faster than MEK, so if you use acetone instead of MEK, then your cement will set up faster. It will also go thick on you again faster too.

And, you should be able to make your own ABS pipe cement by leaving a piece of ABS pipe to dissolve in Methy Ethyl Ketone.

You don't need to know the rest:

If A or B is a hydrogen atom, then it's called an "aldehyde", instead of a ketone. And if BOTH A and B are hydrogen atoms, then it's the simplest aldehyde, called "formaldehyde".

handyguys 03-26-2010 07:57 AM

its possible all those pipes could be moved to expand your closet but there isnt enough info to be able to tell you exactly how without knowing whats connected to what where.

All times are GMT -6. The time now is 12:59 PM.