Does A Washing Machine Need A Vent? (Explained)

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A lot of people question whether their washing machine needs a vent or not.

Like any other plumbing fixture, a washing machine needs a vent to enable the p-trap to do its job. A good vent will stop the sewer gas from getting into the home. It allows air to get into the line. It eliminates the vacuum and makes it difficult for water to drain from the washing machine.

Does The Washing Machine Drain Need A Trap?

A washing machine needs a trap to make the drain efficient. It reduces the chances of exposing the cleaning room to sewer fumes and makes the drain flow as required.

With a p-trap in place, you will be able to install a pipe extending to the washer. Also, if you don’t put the tap in place, it will make the drain overflow or run sluggishly.

Therefore, the best way to effectively drain your washing machine may entail installing a standpipe. This is a pipe that connects to the p-trap and then the drain. But ensure to extend the standpipe above the washing machine to the overflow level.

Luckily, installing a standpipe is easy, especially if there are unfinished walls in the laundry area. All you need is to run a pipe from the drain all the way up to the washer.

But ensure to maintain a slope of ¼ inch for each foot as you move towards the drain. Finally, you will need to glue a standpipe onto the p-trap and use some strapping to fix the standpipe to the stud.

By including a p-trap in the washing machine, it gives the sewer gasses in the pipes a route to escape.

If you don’t do that, the gases that may contain harmful organisms may easily find their way back into the house and harm your family members. Also, sewer gases contain highly flammable methane.

So, if you choose to install the washing machine in an enclosed area and there is no p-trap, it can allow methane to accumulate in the room and lead to a fire outbreak.

Also, after installing the p-trap, it may be necessary that you vent it to reduce building negative pressure inside the pipes. If you allow it to build up, such pressure may render the p-trap nonfunctional.

Also, when you omit the vent, it can result in an overflow. But you must ensure that you place the vent a few feet, probably between 3-5 feet from the p- trap in case of a 2-inch pipe.

Also, once you create a trap, you may need to create some valves to avoid creating a vacuum. Typically, you will install the washing machine on the lower floor. So, when you run the vent upstairs, it may be necessary that you install valves to allow in the air when water is flowing.

A trap on the washing machine is placed behind the washer. Also, you may decide to install it in the wall to allow the used water to flow to the sewer system.

As such, the trap plays an important role in reducing the chance of the gas escaping from the sewer line.

It stops the gas from finding its way into the drainpipe and in the house. It means that the pipe can easily become a channel for transmitting sewer gas back into the house if you cannot install the trap and valve.

Also, every time the washer drains, the water flowing into the pipe may get trapped, and gravity will prevent it from going down the drainpipe. Some water will always be available in the bent section of the drain and will ensure that the gas does not get a chance to travel through the drain into the home.

Thus, when you install your washing machine without a p-trap on its drain line, you make it easier for the sewer gas to flow back into the room. It will make your laundry room unpleasant and will smell like sewage.

Too much of this gas is a health hazard that could cause headaches, unconsciousness, and vomiting.

Other components such as methane are flammable, and so when allowed to build up in the home, they can easily lead to an explosion or result in fire.

Does Every P-Trap Need A Vent?

Vents are important in stopping pressure from building into the sewer line. They should always be placed on the p-trap to reduce the siphoning effect which is likely to leave the p- trap empty.

P- traps are attached to every drain in the home. It holds water and blocks sewer gasses from getting into the drain. But for them to offer this function, they must feature a vent that allows the sewer gases to find its way out. This way, they will not build pressure in the sewer lines. Also, they make it difficult and prevent the siphoning of water from the trap.

Having a properly installed p-trap makes the drain effective. Also, having the vents located at an appropriate distance is important since it helps the trap and the vent to perform optimally.

So, if you are installing a washing machine, you need a professional plumber to help you have the p-traps, and the vents installed appropriately.

But ensure to place the vent near where the pipe connects to the sewer line. If you install it correctly, it will make it difficult for water in the trap to get sucked and so it stops the sewer gases from finding their way back into the room.

Note that the washing machine cannot function well if it does not have a vent.

Normally, the drain pipe will create a negative pressure whenever it drains. So, a vent equalizes the pressure in the drain pipe when water is flowing through the sewer line. It allows the air to escape through the vent.

How Far Should The Vent Be From The P Trap?

How far you place the vent away from the p-trap is critical. It determines whether it does the intended job or not. Typically, if the pipe is 1 ¼ in, the vent should not be more than 30 inches away.

But if you place the washing machine far away from the main building, the drain pipes need to have vents on pipes. But a 2-inch pipe should have a vent after a distance of 8 feet.

Typically, as water flows through the drain pipe, the vent allows the gas to flow up the pipe since it creates a vacuum that forces the gas to pull away from water. Notice that the vent should always come after the trap.

A vent that comes before a trap may not be helpful. Therefore, it should only come after the p-trap, and a few feet away from where the drain connects to the sewer. This way, it is difficult for gases escaping from the sewer to find their way into the room via the washing machine drain.

Installing the vent incorrectly may create problems. For instance, when there is a lot of water going upstream past the point where the machine’s drain pipe connects the sewer line, the rushing water may siphon water from the trap.

So, you need to put a vent line after the p-trap but closer to where the drain pipe connects to the main sewer line.

But you may need to ensure that the washing machine drain pipe does not exceed 2 inches at the point where it connects to the main sewer line. If it is more than 2 inches, you are likely to experience suction issues.


A washing machine needs a vent to reduces the chances of having the gases from the main server line find their way into the house via the washing machine.

Also, it may be necessary to ensure that the vent is placed after the p-trap for optimal results.