# 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.

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.

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

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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