Inch Of Water (inH₂O)

US & ImperialCurrent unit

About 249.089 pascals (the conventional value, 25.4 mm × 9.80665 Pa). Used for air pressure in HVAC and gas appliances.

1 inch of water = 249.08891 pascals (exactly).

About the inch of water

Building services and gas fitting rely on this unit. Manometers filled with water read small differences in air or gas pressure, and in North America the result is stated in inches of water column. Natural gas supplied to appliances is typically 6 to 7 inches WC, and HVAC technicians use it for pressure across coils, filters and ducts. A pipe organ's wind pressure is quoted the same way.

Which water is meant matters a little. Wikipedia gives about 249.082 Pa for water at 4 degrees Celsius, equal to 39.2 degrees Fahrenheit, and also the conventional 249.08891 Pa, which is 25.4 mm times 9.80665 and is the figure used here. NIST lists 249.082 Pa at 39.2 degrees Fahrenheit and 248.84 Pa at 60 degrees Fahrenheit, and some industry standards use 60 or 68 degrees Fahrenheit. About 27.7 inches of water equal 1 psi.

Sources: Wikipedia: Inch of water; NIST SP 811, Appendix B.8

Inch Of Water conversion chart

1 inch of water expressed in every other pressure unit:

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