# vent pipe

#### jimma841

can any body please explain to me the calculation for determing the height of the vent pipe above a 50 gall cistern and the gap between the water level and the pipe.

#### giblets

From the Water Regs G20.3:

"Where vent pipes from either a primary or secondary system terminate over their respective cold water feed cisterns they should rise to a height above the top water level in the cistern to prevent discharge occurring under normal operating conditions."

The calculation given is V = 0.04H + 0.15 where V is the height of vent pipe above the top water level and H is the height from the top water level to the cold water inlet to the hot water cylinder. V & H are in metres. This calc only relates to gravity circulation systems. If a circulation pump is installed due allowance should be made for induced head.

The end of the vent pipe must not be below the top water level in the cistern.

#### lightning

The height to which a vent pipe is to rise above the water level in a cwsc is found by allowing
40mm for every 1m head of waterin the system

for ex the distance between base of boiler and the water level in a cistern is 5m,the vent pipe should be carried up above the water level by a min distance of

5x40+150=350mm

#### jimma841

The height to which a vent pipe is to rise above the water level in a cwsc is found by allowing
40mm for every 1m head of waterin the system

for ex the distance between base of boiler and the water level in a cistern is 5m,the vent pipe should be carried up above the water level by a min distance of

5x40+150=350mm

THANKS TO YOU BOTH.

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