Inch of Water

Inch of Water (inH₂O)

The inch of water is a unit of pressure based on the pressure exerted by a column of water one inch tall at 4°C (39.2°F). It’s particularly useful for measuring small pressure differences in HVAC and medical applications.

Characteristics

• Low pressure unit: ideal for measuring small pressure differences
• Common in: HVAC, ventilation, respiratory therapy
• 1 inH₂O = 249.089 Pa (at 4°C)
• Also written as: in. w.c. (inches water column), iwc
• Temperature dependent: standardized at 4°C/39.2°F

Applications

• HVAC system pressure drops and fan static pressure
• Clean room differential pressure monitoring
• Respiratory therapy and ventilator settings (CPAP, BiPAP)
• Gas appliance pressure specifications
• Duct pressure measurements

Conversions

• 1 inH₂O = 0.249089 kPa
• 1 inH₂O = 2.49089 mbar
• 1 inH₂O = 0.0360912 psi
• 1 inH₂O = 0.0735559 inHg
• 1 inH₂O = 1.86833 mmHg