Inches of water is a non-SI unit forpressure. It is also given asinches of water gauge (iwg orin.w.g.),inches water column (inch wc,in. WC," wc, etc. or justwc orWC),inAq,Aq, orinH2O. The units are conventionally used for measurement of certain pressure differentials such as small pressure differences across an orifice, or in apipeline or shaft,[1] or before and after a coil in anHVAC unit.
It is defined as the pressure exerted by a column ofwater of 1inch inheight at defined conditions. At a temperature of 4 °C (39.2 °F) pure water has its highest density (1000 kg/m3). At that temperature and assuming thestandard acceleration of gravity, 1 inAq is approximately 249.082pascals (0.0361263 psi).[2]
Alternative standard 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; it is conventionally equated to 2,989.067 pascals (0.4335275 psi).[3]
InNorth America, air and other industrial gases are often measured in inches of water when at low pressure. This is in contrast toinches of mercury orpounds per square inch (psi, lbf/in2) for larger pressures. One usage is in the measurement of air ("wind") that supplies apipe organ and is referred simply asinches. It is also used innatural gas distribution for measuring utilization pressure (U.P., i.e. the residential point of use) which is typically between 6 and 7 inches WC or about 0.25 lbf/in2.
1 inAq ≈ 0.036 lbf/in2, or 27.7 inAq ≈ 1 lbf/in2.
| 1 inH2O | = 249.08891 pascals[3] |
| = 2.4908891mbar orhectopascals | |
| = 2.54cmH2O | |
| ≈ 0.002458316 atm | |
| ≈ 1.868320 Torr ormmHg | |
| ≈ 0.0735559 inHg | |
| ≈ 0.03612729 lbf/in2 |