The unit used to express common operating gas pressure for natural gas is inches of water column.

• A. Atmospheres
• B. PSI
• C. Bar
• D. Inches of Water Column

Answer: (D)

Gas pressure in natural gas systems at the appliance is a very small pressure difference relative to atmospheric pressure, so it’s measured in inches of water column. This unit directly reflects the height of a water column needed to balance the gas pressure, which matches how regulators and burners operate—at only a few inches of water column. A typical operating range at the appliance is roughly half to a couple of inches of water column, which would be awkward to express with larger units.

Other common pressure units like atmospheres, PSI, or bar measure much larger pressures and aren’t practical for those small operating pressures in natural gas systems, making them unsuitable for everyday appliance settings. For reference, 1 inch of water column is about 0.036 psi, illustrating how tiny these pressures are.

So, inches of water column is the standard unit used to express common operating gas pressure for natural gas.