Inch of water
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Inches of water, inAq, "Aq or inH20 is a non-SI unit for pressure. It is used for measuring small pressure differences across an orifice, or in a pipeline or shaft.[1]
It is defined as the pressure exerted by a column of water of 1 inch in height at defined conditions for example 39 °F (4 °C) at the standard acceleration of gravity; 1 inAq is approximately equal to 250 pascals at 0 °C.
Alternative standard conditions in common usage are 60 °F, or 68 °F (20 °C)
Its most common usage is in the measurement of air ("wind") that supplies a pipe organ and is referred simply as inches. Standard wind pressure in the organ is typically around 3 to 4 inches but some high-pressure stops can be on 25 inches or more.
It is also used in natural gas distribtuion for measuring utilization pressure (U.P.) which is typically between 6 and 7 inches or .25 psi.
