Bathroom vanity venting?

Is there a limit to how far you can run horizontally with a 1-1/2 inch vent before you go vertical or tie into a stack? Present vent by previous owne r runs about 15 feet. I could tie it into a 4" stack only 4 feet away. Eve rything is still open (basement) and accessible. Cutting a 4" vertical cas t iron stack would not be fun, but maybe there are other methods of tying i n.
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Ivan:
In a case like that, you should probably consider using an air admittance valve.
You see, the whole idea behind vent piping is to prevent the partial vaccuum that can be created behind draining water from sucking the water out of the drain's P-trap. By connecting an empty pipe (called a "vent") to the drain pipe a short distance downstream of the trap, air will be sucked into the drain pipe behind the draining water instead of the water in the p-trap being sucked out.
An air admittance valve (also called a Studer valve after the company that first marketed them) is really nothing more than a spring actuated check valve. You mount it on the drain pipe a short distance downstream of the P trap. If a partial vaccuum ever develops in the drain pipe behind the draining water, the air admittance valve opens allowing air to rush into the drain pipe behind the draining water, thereby ensuring that there's no risk of the water in the p-trap getting sucked out.
You see, the worst that can happen if the water in your p-trap gets sucked out is that you have the smelly air in the sewer coming up through that empty trap to stink up your bathroom. That sewer gas isn't pleasant, but it's not poisonous either. So, it's best to have your drains vented, but where venting isn't practical, most jurisdictions will allow you to use an air admittance valve instead.
Google "air admittance valve" or "Studer valve" and read all about them.
--
nestork


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Ivan Vegvary wrote:

The air admittance device is probably the easiest option. The height of the device is supposed to be above the fixture that it is venting.
Cutting the cast iron vent stack and inserting a tie-in there is an option, but it can be tricky. For one thing, the pipe/stack above the cut needs to be braced well so it doesn't drop down when you take out a section of the stack.
I noticed that you recently posted:
"Sheet vinyl vs. tile??", and, "Circuit Breaker as an input device",
and you received lots of replies to both questions. But, I didn't see any reply back from you. Did you read what people wrote? Do you have ANY follow-up on either of those questions and the responses that you received?
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