Edited by Maluniu, IngeborgK, BR, Zohaib Ahmed Abbassi and 2 others
Understanding the Basics
Proper ventilation is an important part of a plumbing system. Every
plumbing fixture, from a toilet to a shower, needs to be connected to
ventilation piping. The pressure of outside air drawn in from
ventilation pipes helps push waste or used water down through drain
pipes. Vent pipes also lead through a roof to expel harmful gases or
unpleasant odors from a home. Try these steps to vent plumbing.
Method 1 of 3: Understanding the Basics
Familiarize yourself with local plumbing and building codes.
These will have restrictions about the size and material of your
piping, the distance between certain fixtures and vent pipes, and the
placement of ventilation. Some codes also require permits or
professional help for certain projects. Make sure you understand your
local codes in detail before beginning your project, and consult a local
plumber if you have questions or want advice.
- Building codes change often to reflect current knowledge about safe
and effective materials and building standards. Make sure you use the
most recent local codes.2
- Choose a pipe material for your ventilation system.
Consider which pipe material best fits your needs, budget, and any
existing piping. Most ventilation systems use small pipes less than ten
inches in diameter, which allows plastic pipes like PVC or ABS pipes. In
certain situations these can lack strength or durability, so copper,
steel, or cast-iron pipes are also available. In choosing a pipe,
consider strength, durability, flexibility, weight, resistance to
corrosion, and methods for joining pipe. 
- Both PVC and ABS pipes are non-toxic and resistant to abrasion. ABS
pipes are easier to install than PVC, and are tougher and more rigid,
but are also more likely to warp or deform in the sun. PVC pipes are
flexible but durable. Both kinds of plastic pipe are cheap compared to
metal or other pipes.
- Consider the pressure class of the pipe. If you anticipate a lot of
pressure in your pipes, go for a higher pressure class. For most
projects, class 160 or 200 PVC is sufficient. The cost difference
between the two classes is negligible, so people often choose the
heavier duty 200 class pipe.
- Consider size constraints.
The size of pipe you use both for ventilation and for drain or waste
pipes dictates the number of fixtures you can tap into the pipes. It
also limits the distance between fixtures and their drainages. Larger
pipes will give you more freedom in terms of both distance between
fixtures and number of fixtures, but using only large pipes can be
unnecessary. Examine local building codes for regulations about vent,
drain, and waste pipe size.
- Understand the waste pipes in your building.
Waste pipes remove water and waste from a toilet. Your building has a
large-diameter, central pipe that is the control center of the
wastewater system. From here, waste is carried to your sewer or septic tank.
- Learn about your building's drain pipes.
Drain pipes carry water from sinks, showers, tubs, and other
appliances. They often are equipped with a P-trap, or a bend in the pipe
just below the sink or other fixture, in the shape of a P. This traps
water in the bottom of the P, blocking the pipe and preventing gases and
odors from escaping into your house through the drain pipe. The water
in the P-trap is refreshed every time more water runs through the drain
- Understand how vent pipes work.
Vent pipes run from waste or drain pipes upwards, ending outside the
building, usually sticking up through the roof. This allows unpleasant
and potentially dangerous odors or fumes to safely leave your plumbing
system, escaping harmlessly into the air outside. It lets air into the
system, filling the vacuums left by water moving through the pipe. This
allows water to flow quickly and smoothly through the pipes.
- Understand the general layout of piping.
Vents and other vertical pipes should be as straight as possible to
prevent condensation from building in the pipes. Horizontal pipes should
slant down toward fixtures so that gravity can push waste and water
through the pipes. These commonly run with a slope of 1/4 inch down for
each horizontal foot of piping.
- Visit a hardware store to get pipe, fittings, and materials for joining and supporting your vent stack.
Measure the amount of pipe you'll need before coming in, and ask store
employees to help you cut your pipe down to size. Buy fittings to attach
pieces of pipe together and accommodate corners, and choose your
fittings based on the type of pipe you'll be using.
- Employees at hardware stores are often knowledgable about various
projects you might undertake and can answer questions or offer
suggestions if you're unsure about anything. They can also refer you to
professionals who will be able to help more thoroughly with your
Method 2 of 3: Dry Venting
1Understand dry venting.
This is a simple system in which each fixture has its own vent pipe. It
is simple to plan and implement, because you won't have to worry about
placing different fixtures close enough together or using pipes big
enough for multiple fixtures. Each vent is a small, isolated pipe that
you can work with separately. However, having a different vent pipe for
each fixture will mean that you have a lot of vent pipes running up
through your building and out your roof. This uses a lot of unnecessary
piping, and you'll be doing more work than you need to.
2Create a dry vent by attaching a ventilation pipe to a fixture's drain pipe.
Depending on the fixture, the vent pipe can be fairly small but should
be positioned within a couple feet of the fixture. Make sure to check
your local building codes for specific regulations about sizes and
distances for your vent pipe.
- A common layout is to have a drain pipe run horizontally away from a
sink or other fixture for up to two feet. Then the drain pipe will join
with a vertical pipe. Down from the join, this vertical pipe acts as a
drain for the fixture. Up from the join, it vents the fixture.
3Extend the vent pipe outside the building according to building regulations.
Usually, the vent pipe must extend six inches above the roof or 12
inches away from vertical walls, but double check your building codes
and requirements to make sure.
4Repeat the ventilation process with any other fixtures you're installing.
Make sure every fixture has a vent pipe associated with it so that your
whole plumbing system will run quickly, smoothly, and safely.
5Vertical ventilation pipes called vent stacks provide air circulation to any part of the plumbing system.
Vent stacks can run parallel with waste pipes to ensure proper
ventilation in tall buildings. Sub-vents may be branched together to
exit 1 vent stack, allowing for only 1 hole in the roof for ventilation.
Method 3 of 3: Wet Venting
1Understand wet ventilation, where one fixture's vent is another's drain.
Under this system, you can install several different fixtures in the
same system of pipes, attached at different places. Although this system
complicates the layout of your plumbing system, it reduces the total
amount of piping you need and can save a lot of space and effort.
2Plan the location and layout of your piping.
Consider asking a professional plumber to help you with this. Consider
the size of piping you'll need for each segment, the distance between
fixtures, and the plumbing demands of each fixture. Make sure your plans
fit within building codes and regulations, which can be more
complicated for wet venting than for dry.
- An example bathroom layout is as follows. The sink has a drain pipe
1.5" in diameter, which connects to a vertical vent pipe. The toilet has
a 3" waste pipe which makes a T or a Y with the bottom of the vent
pipe, such that the vent pipe goes upwards vertically from the
horizontal waste pipe. Between the intersection with the sink's drain
pipe and the toilet's waste pipe, the vent pipe is acting as the sink's
drain and the toilet's vent, and so must be 2" in diameter. Above the
intersection with the sink, the vent pipe simply acts as a vent for both
fixtures and so can be smaller, 1.5" in diameter.
3Accommodate regulations in wet venting.
For example, toilets should be installed downstream of all other
fixtures, so that nothing else will vent through the waste pipe. A wet
venting pipe can't be reduced in size -- the piping should never get
smaller as other fixtures tap into it. And all fixtures should be no
more than the maximum allowable distance from a vent, even if that means
dry venting certain fixtures.
- See your local building codes for more detailed regulations, and
double check that you accommodate all of them. Run your plans by a
professional plumber or someone intimately familiar with these codes if
you're unsure about any of the regulations.