How Many Fixtures on a 3 Inch Vent Is the Standard for Plumbing

How Many Fixtures on a 3 Inch Vent

Whenever you are building a new house or renovating an old one, the most important thing right after electrical work is plumbing. And it is a great deal, as most of our life is spent near the kitchen sink, bathtub, or sink. 

No matter what type of cleaning you are doing, water will be involved. And proper hygiene is insured if you have a good plumbing system. 

It’s a bit critical and needs a little calculation. But we are all about saving and efficiency. That is why today we are going to talk about how many fixtures on a 3 inch vent is ideal. 

We won’t assume anything but guide you with the International Plumbing Code (IPC) guidelines. So let’s dive into it. 

Plumbing Guide: How Many Fixtures on a 3 Inch Vent Are the Maximum

First of all, you cannot just assume and go with it when it is about your house’s plumbing system. You don’t want water and waste flooding your apartment! 

There are strict rules regarding the venting system. How many fixtures can go on a certain width of vents, what type of deposits we are dealing with, and what is the speed of the deposit, it all comes into consideration.

We know it’s a lot to take in. That is why we have made it simple in our article for 3 inch vent fixtures. 

The Theory of Plumbing and Vents

The wise plumbing genie says, In plumbing, a Fixture Unit (FU) or Drain Fixture Unit (DFU) is “a unit of measure, based on the rate of discharge, time of operation and frequency of use of a fixture, that expresses the hydraulic load imposed by that fixture on the sanitary plumbing installation”.

Makes any sense? This means that the higher rate of usage and discharge on a certain fixture needs a bigger venting unit. And if that is so, you won’t be able to direct a lot of fixtures in just one 3-inch vent. 

It will clog up eventually and we all know how bad it gets in a house. Nobody wants to hunt in the river of waste and water to unclog it. So it is best you plan ahead. 

How Many Toilet Fixtures In a 3 Inch Vent

For any 3-inch vent, you can have only 2 toilet fixtures. It is not only the instructions of the IPC but also suggested in Universal Plumbing Code (UPC). 

The reason for that is when a toilet is flushed, about 1.6 gallons of water is flushed down the fixture. And there is a need for room to discharge that amount of water and waste right away. 

That is why the drainage pipe is also 3 inches like the 3-inch vent. 

So if you simultaneously flush more than two toilets, the drainage and air vents won’t be able to move such an amount of water in a short time. Meaning it will clog up and the waste won’t be discharged. 

At the same time, if you have two toilets in the same area or side of the apartment, one 3-inch vent will work. But if two toilets are in separate locations, you will have to use two different vents. 

How Many Sink and Shower Fixtures Can Go in a 3 Inch Vent

There is no exact number of how many sinks, showers, and tubs can share a vent. It can go up to 24 drainage lines sharing a 3-inch vent. 

But it mainly depends on the area you live. The building code differs in each area and it is better to follow it. 

Frequently Asked Questions 

How many toilets can be on a 3 inch vent?

The standard number of toilets using a single 3-inch vent is 2. It can go up to 4 but will need 2 air vents on the roof to create the needed air pressure. Otherwise, the deposit will not pass in time. 

How many fixtures can be on a 3 inch drain?

Sink, tub, and shower fixtures can go in the same 3-inch drain. The number can go up to 24 fixtures if needed. But it mainly depends on the area you are in. the plumbing code is different in different states and regions. So make sure you learn it before planning your drainage system. 

How many plumbing fixtures can you have on one vent?

There can be two to 10 fixtures connected to one open horizontal vent. But not more than 2 of the same type of fixtures can be connected to one vent. Which makes it a bit tricky to figure out what type of fixtures to add in one single vent. So better consult with your plumbers for more info and ideas. 

How many fixture units does a 3 inch wet vent have?

You can have two of each kind of fixture in a 3 inch wet vent. And the number of fixtures can go up to 10 depending on your apartment size. 


Sometimes more is not better. Especially for drainage lines and vents. The more fixtures you will add to it, the more complicated it gets. So keep regular water flow in one vent, and wastage water of the toilet in another. And overcrowding one single vent is never a good idea. Rather you can go for a bigger vent than a 3-inch one or use a 4-inch drainage pipe. This will allow you to pass more deposits faster without clogging anywhere.

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