Inches of water is a non- SI unit for

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

. It is also given as inches of water gauge (iwg or in.w.g.), inches water column (inch wc, in. WC, " wc, etc. or just wc or WC), inAq, Aq, or inHO. The units are conventionally used for measurement of certain pressure differentials such as small pressure differences across an orifice, or in a

pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (computing), a chain of data-processing stages or a CPU optimization found on ** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...

or shaft, or before and after a compressor in an HVAC unit. It is defined as the pressure exerted by a column of

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

of 1 inch in

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For example, "The height of that building is 50 m" or "The height of an airplane in-flight is ab ...

at defined conditions. At a temperature of 4

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...

(39.2 °F) pure water has its highest density (1000 kg/m³). At that temperature and assuming the standard acceleration of gravity, 1 inAq is approximately 249.082 pascals. Alternative standard conditions in uncommon usage are 60 °F (15,6 °C), or 68 °F (20 °C), and depends on industry standards rather than on international standards. Feet of water is an alternative way to specify pressure as height of a water column in United States customary units. In North America, air and other industrial gases are often measured in inches of water when at low pressure. This is in contrast to

inches of mercury Inch of mercury (inHg and ″Hg) is a non- SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States. It is the pressure exerted by a column of mercury in heigh ...

or pounds per square inch (psi, lbf/in) for larger pressures. One usage is in the measurement of air ("wind") that supplies a pipe organ and is referred simply as ''inches''. It is also used in

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

distribution for measuring utilization pressure (''U.P.'', i.e. the residential point of use) which is typically between 6 and 7 inches WC (6~7″ WC) or about 0.25 lbf/in. 1 inAq ≈ 0.036 lbf/in, or 27.7 inAq ≈ 1 lbf/in. :

References

{{reflist, 30em Units of pressure

See also

References