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It is my understanding that draining into a pipe of sufficient size will
negate the need for a vent stack and that this techniqe is known as a
‘wet vent’.
If the above is correct, and I have a 1 1/4″ tailpiece from a sink
draining into a 1 1/2″ p-trap that immediately drains into a 2″ line, is
that 2″ line big enough to be a wet vent, or do I ABSOLUTELY need a
vent continuing up?
What is the rule for sizing a drain line so that it can act as a wet vent
and not suck the p-trap dry?
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Replies
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Try this link to learn about wet vents.
I believe that you need a vent.
If you have conditions that prevent conventional or wet venting, consider using an air admittance valve, also know as a Studor vent, but, check your local code first.
*A wet vent is still a vent, it just has several lines draining into on it way out the roofDavid
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Want to know the easiest way????
Go to the hardware store and ask the attendent for an "auto-vent" (in Canada they go for under $10). I've used them in the past when I need a vent but do not want to run another vent stack.
It work much l;ike a one-way value and only draws air into the pipe when the needs exists - Great little unit!
Evan
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If you use a Studor (or autovent) vent, it must be accessable. That means a panel door to get to it.
Used several in a hotel remodel. They're a great idea but can malfunction and if a drain gets clogged, they could overflow (although all the sinks toilets, and showers below it would have to be clogged too.) and they can let sewer gasses into the home if they malfunction.
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Geoffrey-
A wet vent operates on the idea that a section of drain pipe, if oversized, can operate as both a drain and a vent. The wet vent section must be oversized by 1 pipe size. It has to be in a vertical drain line and can only serve one story of the building. The wet vent does not eliminate the need for a vent, it allows a portion of the venting system to be both drain and vent. An example would be if you were draining a lavatory into the vent from a water closet drain. Normally, the water closet drain vent is required to be a 2". If you increased the water closet drain vent to 2-1/2", then it can serve the purpose of both a drain for the lav and a vent for the water closet. Look in Chapter 9 of the Uniform Plumbing Code for a description of wet venting.
Another option would be a combination waste and vent system. This is where a horizontal run of pipe can serve as both drain and vent. This is oversized by 2 pipe sizes and can only be used where structural considerations prevent the installation of a normal venting system. Design has to be approved by your building official. Combination waste and vent systems are seen commonly on floor drain applications. Again, look at UPC Chapter 9.
Proper venting is really important in plumbing. Without venting the system, traps will be siphoned and potentially harmful sewer gasses will enter your house. You may want to consult a local plumber as codes vary.
Good luck!
Sami
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It is my understanding that draining into a pipe of sufficient size will
negate the need for a vent stack and that this techniqe is known as a
'wet vent'.
If the above is correct, and I have a 1 1/4" tailpiece from a sink
draining into a 1 1/2" p-trap that immediately drains into a 2" line, is
that 2" line big enough to be a wet vent, or do I ABSOLUTELY need a
vent continuing up?
What is the rule for sizing a drain line so that it can act as a wet vent
and not suck the p-trap dry?