How Many Plumbing Vents Should a House Have?

Plumbing vents are one of the unsung heroes of your plumbing system. They’re small pipes sticking out of your roof that create airflow. There’s no one-size-fits-all approach to figuring out how many plumbing vents a house should have. Here are some key factors that’ll give you the insight you’re looking for, whether you’re building a new home or improving your existing one. 

What’s a Plumbing Vent?

Plumbing vents are an essential part of your drainage system. While the pipes are responsible for carrying the wastewater out of your home, your plumbing vents do the following: 

• Provide airflow

• Balance the pressure in the pipes

• Carry sewer gases and smells up and out of the house

There are six types of plumbing vents, although your home may have only a few of them. The vent types that all homes have are the main vent stack and branch vents. 

The main vent stack is, as the name suggests, the main pipe. It starts in the basement and goes all the way up through the roof of your house. Branch vents connect drainpipes in the home to the main vent.

Every home plumbing system needs one main vent stack and two or more branch vents to work properly. Depending on the size of the home and the number of stories, you’ll need multiple main vent stacks and a variety of vent types.

Factors that Affect the Number of Vents You Need

Each plumbing fixture and drainpipe requires a vent, so the actual amount you’ll need depends on the number of fixtures you have. This includes all of your sinks, bathtubs, showers, toilets, and washing machines. Note that in many instances, multiple fixtures are on a single vent system, like in the bathroom.

Bigger homes require more than one main vent stack, especially if your fixtures are scattered throughout the house. Another factor to remember is your local building codes. These will specify how many vents you need, their size, and location requirements.

Here are some rough estimates of the number of vents you’ll need according to the house size, assuming that it’s a one-story house with one kitchen and a laundry room:

Additional Factors to Consider

Many homes will utilize more vent types other than main vent stacks and branch vents. Here are the other vent types available:

• Loop vents are commonly used for kitchen islands. They’re an alternative to installing a vent pipe through the ceiling. The vent forms a loop under the sink and connects to the main vent.

• Auxiliary vents allow you to vent individual fixtures that are too far from a main vent stack.

• Wet vents allow you to use one vent for all the fixtures in your bathroom. This pipe vents air from a fixture. 

• Air admittance valves prevent dangerous gases from leaking when roof venting isn’t an option.

Note that you need an extra main vent stack for each floor, so expect to need at least two main vent stacks for a two-story home. The further apart your fixtures are, the more likely you’ll need additional main vent stacks.

What Happens if a Home Doesn’t Have Enough Vents?

If a home doesn’t have enough vents, you’ll have a wide range of issues, including some that can be dangerous to your health. Poorly designed or improperly installed venting systems can trap sewer gases and odors in the home. 

According to the Centers for Disease Control and Prevention, exposure to sewer gases can cause a wide range of health complications, including respiratory issues, loss of smell, and loss of consciousness. If you notice sewer smells in your home, vacate immediately and call an emergency plumber for assistance.

In addition to sewer smells, a lack of proper vents can cause slow drainage, frequent clogs, gurgling sounds, and water backups in sinks and toilets.

Avoid all of these issues by hiring a plumber near you to install plumbing vents. Your pro can evaluate your home and make recommendations that line up with building codes.