HVACR Glossary
 

Inches of water
A unit of pressure equal to the pressure exerted by a column of liquid water one inch high at sea level and at a temperature of 39.2°F. One inch of water column equals a pressure of 0.578 ounce per square inch at sea level and at a temperature of 39.2°F. One inch of water column equals a pressure of 0.578 ounce per square inch(.036 psi). One inch of mercury column equals about 13.6 inches of water column. Approximately 1/28 of one psi.