How to Vent Plumbing Video
How to Vent Plumbing
AsktheBuilder.com founder, Tim Carter, is also a master plumber. He shows RARE video of plumbing vent pipes in an attic and walls before they disappear forever behind drywall.
Carter installed the vent pipes for this plumbing himself in a new home in central New Hampshire in the winter of 2016. (Read his May 31, 2020 Newsletter about this build and how he helped another couple.)
He talks about the importance of installing a full-sized vent on at least one stack all the way from the base of the stack up and through the walls and then through the roof.
There's been a disturbing trend away from using a full-size vent in new homes. Many plumbers feel small 1.5 and 2-inch vent pipes will be enough to vent an entire home.
Small vent pipes can choke off on the inside with ice in bitter cold climates. When you use a full-sized 3 or 4-inch vent, it takes much more ice to close off the vent pipe.
The plumbing vent pipes create a pathway to let air from outdoors back into the plumbing system when water is rushing down the drain pipes.
This column was so popular, it appeared in the February 9, 2016 AsktheBuilder Newsletter also.
Why does the 2" master shower drain pipe connect to a 1 1/2 inch drain where it enters the 1 1/2 inch vent pipe? If a 2 inch drain is "required" (your words) why after about 3 feet does it choke down to 1 1/2 inch ?
The drain is a 2" drain and has a 2 x 1.5 x 2" san t under floor.
why would you run the vent pipe system the entire length of the house when you could have installed two or more vent pipes that would go through the roof at the other end of the house to provide the necessary vent system and save all that extra piping.
REPLY ADDED BY TIM CARTER:
For some reason I can't add a reply the normal way so here goes:
1. Because the owner only wanted one roof penetration.
2. Because it could be far cheaper to have one vent when the BEST vent flashing costs $60 each (2016 prices).
3. The current cost of 1.5-inch PVC is just over 50 cents a foot. That means you can run lots of it across the house to get to the primary sole vent before you exceed the cost of the second $60 flashing.
4. Smart plumbers and homeowners put vent pipes where they are RARELY seen. Lazy plumbers - and others who want to cut corners - put them popping out of roofs wherever they want, even if by the front door!
Very instructive video, Tim. Thank you for taking the time and effort to show and explain how a proper vent system is installed.
THANK YOU Tim for constantly making me smarter! One question - I have a kitchen island with my sink and dishwasher. There is no area that a vent pipe can go UP and connect to a vent pipe. Bad design?
I notice that the pipe work you did is done early - after framing - before HVAC or electric. Good to know.
Perhaps Beth has the same thing we do at a couple sinks, which is a local vent that connects near the J-trap and is like a little slotted cylinder sitting under the sink. This was done by a previous remodeler in a couple places where sinks were relocated. Seems to be fine! Our own plumber didn't LOVE it, but says it works and meets code. I am curious about Tim's view on this.
Waiting for Tim ;o)...which would you rather have? More chances for a leaky roof or an extra run of vent pipe for the plumbing? Most roofs start leaking first at the penetrations. The fewer through-the-roof vents the better.
Changing gears...those devices that vent a sink, etc, where there is no wall to directly run a regular vent are called air admittance valves (AAVs). They've been around a long time and are nearly universally approved for use under some circumstances. A home will always require at least one (standard) through the roof plumbing vent. Besides island kitchen sinks, AAVs can be used in some remodeling situations. They must be accessible and not hidden in walls.
There are also other venting schemes for island sinks that are more complicated than the simple, easy to use AAV (both of) which let air into the system.
Why do you have the kitchen sink drain in an outside wall? Looks like a sure freeze situation, especially in NH!
Drain lines in exterior walls are not an issue in NH. That's a 2x6 wall for starters, there will be insulation between the pipe and the exterior sheathing and the wall cavity may never get below 32F. Remember, the wall cavity is almost always some temperature that's between the interior and exterior air temperatures.
thank you for this very informative video. all these years I thought that a vent was for air to go out not be sucked in. I thought that when you flushed a toilet and ran water down a sink that the air in the pipe had to "vent out some how" and that was what the vent was for. if I understand right it creates a vacuum so it needs air to replace or assist the fluid moving?
Mike,
TNX as we say in Morse. If you remember your high school physics, then you may remember Daniel Bernouilli. Liquid flowing past something creates a partial vacuum of sorts.
Also, as I stated in the video, think about the entire plumbing system in your house BEFORE any water goes down a drain. It's in a state of equilibrium. But as soon as you dump 1.6 gallons of water into the drain pipe when flushing a toilet, the water displaces 1.6 gallons of air. That air needs to be *replaced* and that's what the vent pipes are for.
If that rushing water in the drain pipe roars past a wye or tee fitting in the drain system, it creates a vacuum at that point. If there's no vent pipe, or a clogged one, attached to that branch in the system, the vacuum can be so strong it will syphon the water from the fixture trap.
All you have to do is ask my good friend Dave Evans if he vented his kitchen sink 30 years ago, the drain line upstream from his washing machine drain!
The answer is NO. And each time his washing machine pump pushed lots of water at once into the drain pipe you'd here the "schlooooooooooooo" sound at his kitchen sink as the water in the trap under the sink was sucked down the pipe.
I'll never forget the day I caught him in his lie. He said, "Yes, I vented that line...." He sits on a throne of lies... 😉
I am having critter control put wire mesh over each of our roof vents.
Very nice video with the exact explanation of a vert pipe. Have always dislike the (too) many roof pipes for venting in most houses. Thank you for this video!
great eplaination of vent pipes.