How to Size a Water Tank Vent AWWA D100

Written by louis gutierrez
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How to Size a Water Tank Vent AWWA D100
Air vent allows water to flow out faster from the water tank. (Jupiterimages/ Images)

Sizing the air vent of a American Water Works Association (AWWA) D100 tank is important to allow proper flow of water out of the water tank. The water tanks are manufactured with an opening for the air vent piping. The important part when sizing the air vent is the length of the piping that will connect to the air vent opening on the tank. The length of the air vent piping will vary depending on the location of the water tank.

Skill level:

Things you need

  • Tape measure

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  1. 1

    Install the water tank in its permanent location. If your water tank is going underground, install it in its location but do not cover the top with soil.

  2. 2

    Measure the distance from the tank vent opening to the roof surface or any surface that will cover the water tank. If your water tank will not have any surface covering the roof, do not measure anything and use a pipe at least four inches long.

  3. 3

    Add four inches to the distance from the tank vent opening to the roof surface. This will give you the minimum height you can size the vent piping, as you must provide a minimum of four inches between the roof surface and the vent cap, which will go at the top of the vent piping. To be on the safe side, you can add two extra inches to your distance, as this will make sure the minimum distance is met.

Tips and warnings

  • If you want to verify your vent pipe size is correct, contact your county's local building department.

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