How to Vent Plumbing

Edited by Maluniu, IngeborgK, BR, Zohaib Ahmed Abbassi and 2 others

Three Methods: Understanding the Basics Dry Venting Wet Venting

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. ^[1]
- 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.^[2]
- 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.^[3]
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.^[4]

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.^[5] 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 pipe.

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 project.

Method 2 of 3: Dry Venting

1
Understand 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.^[6]
2
Create 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.
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Extend 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.
4
Repeat 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.
5
Vertical 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

1
Understand 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.
2
Plan 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.^[7]
3
Accommodate 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.