Does a Plumbing Vent Have to Be Straight?


The plumbing system in any building will also have plumbing vents running alongside the drains. No good plumbing system can function without a good and effective network of plumbing vents.

But what are plumbing vents? Are they the same as plumbing drains? What purpose do they serve? The following sections will explain what plumbing vents are and why they have to be straight:

Are Plumbing Vents Necessary?

The whole purpose of a plumbing vent is to make sure that an adequate amount of air pressure is maintained in the plumbing system. The plumbing vent allows fresh air to enter the plumbing system, which in turn ensures that the whole system is functioning well. The air pressure will keep things moving along and is an extremely important element in the plumbing system as that is what makes sure that there are no clogs.

Also referred to as a vent stack, the plumbing vent is also responsible for getting rid of gas and odors from the system. If the whole system was shut off with no fresh air passing through, it would start stinking up the whole room.

If you do not want your bathroom or kitchen to smell like sewage, your plumbing system requires vents for maintaining air pressure.

What Happens If There Are Bends in the Vent?

Now, what happens if there are bends in the plumbing vent? If the plumbing vents are vertical, they need to be straight or you will be risking clogging and blockages. If there are turns and bends in the vent, you will be risking vapor locks.

The turns in the vent may end up trapping moisture. Even the fresh air that is coming through the vents will not be effective if there are sharp bends in the vertical vent.

For example, if you ever try to empty a bottle with a narrow mouth, you will find that it takes very long and empties quite slowly. But if you drill a vent at the other end of the bottle, it will allow the air to enter the bottle and push the water out more effectively.

Now, imagine if the bottle had curves and bends. It would make it twice as hard to get the water out as the exit path becomes even more complex. Even after the bottle has been emptied out fully, you may still find that there are droplets of water still left behind on the bends.

In the same way, if there are bends on a vertical plumbing vent, it will make it more difficult for air pressure to be created as there is no straight path for the air to travel through. The acceleration will slow down as the bend will create a hindrance. Therefore, if the plumbing vent is vertical, it needs to be straight.

Can Plumbing Vents Run Horizontally?

While vertical vents are meant to be straight so a blockage can be prevented, does that mean that plumbing vents cannot be horizontal? Plumbing vents are quite frequently placed horizontally, depending on available space and other logistical concerns.

However, the same applies to the vent when it is horizontal. One should avoid bends and turns in the vents to ensure that there is no possibility of a trap. If it is being placed horizontally, ensure that it is at an angle no more than 45 degrees.

Essentially, the vent pipe needs to be dry at all times. Any possibility of moisture collecting in bends or other obstacles and the purpose of the plumbing vent will be defeated.

They are typically installed from the top of the drainpipe, coming down completely straight if they are vertical or at an angle not more than 45 degrees to the horizontal. If water backs up into the plumbing vents, then you know there is a problem in its installation that needs to be rectified as soon as possible.

Where Are Plumbing Vents Located?

If you are not sure where your plumbing vents are located, there are three places you can start by looking. Firstly, locate your plumbing main plumbing drain line. It will typically come from underneath the house, in a basement or crawlspace.

The line may be made of cast iron or of a PVC pipe that is typically painted black. The plumbing vent should come straight down along with your main plumbing line.

If you have an attic, you can also check for a plumbing vent. If there is any pipe running from the floor straight up the ceiling of the attic, it is likely your plumbing vent. It may be capped at the ceiling, or it may go up till the roof. If your house has more than two bathrooms, you may even find two plumbing vents in the attic.

Finally, take a ladder to the roof. If there is any pipe that extends a little over the roof and it is not the chimney, chances are it is a plumbing vent of some kind.

Can Plumbing Vents Freeze?

Yes, your plumbing vents can most certainly freeze up during cold weather and sub-zero temperatures. This can become quite problematic as when the vents don’t function, it could lead to harmful sewage gases accumulating in your home.

If you live in a region that experiences harsh winters, it is important to cover the vent stacks with good insulating material.

Add extra insulation where the air enters the vent at the base of the stack. If the vent has already clogged with frost, it may be useful to pour hot water down the vent. Use a hose that is graded for hot water. That is easier and safer than climbing up to the roof with a pail of hot water.

Final Thoughts

Plumbing vents are important for maintaining air pressure that will prevent clogs in your drains. But most importantly, they expel harmful sewer gases that would otherwise build up in the drains without a steady flow of fresh air. It is not enough to simply install drains in your plumbing system. The vents are just as important, if not more.

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