What unit is used to measure gas pressure in HVAC systems, as commonly specified for operating ranges?

What unit is used to measure gas pressure in HVAC systems, as commonly specified for operating ranges?

• A. PSI
• B. Pascal
• C. Inches of water column
• D. Bar

Answer: (C)

Gas pressures in HVAC systems are measured in inches of water column because the pressures involved are very small, and this unit provides a practical, intuitive scale. The idea is that a column of water of a certain height exerts the same pressure as the gas at that point, so readings stay within easy-to-read ranges on gauges and manometers. For context, 1 inch of water column is about 0.036 psi (roughly 249 Pa), so typical operating ranges for gas appliances—only a few inches of water column—translate to small, manageable numbers. Using psi would yield tiny fractions that are harder to read in the field, while pascals aren’t the common go-to in HVAC practice, and bars are far too large to capture these small pressures. That’s why inches of water column is the standard unit used to specify gas pressure operating ranges.

Gas pressures in HVAC systems are measured in inches of water column because the pressures involved are very small, and this unit provides a practical, intuitive scale. The idea is that a column of water of a certain height exerts the same pressure as the gas at that point, so readings stay within easy-to-read ranges on gauges and manometers. For context, 1 inch of water column is about 0.036 psi (roughly 249 Pa), so typical operating ranges for gas appliances—only a few inches of water column—translate to small, manageable numbers. Using psi would yield tiny fractions that are harder to read in the field, while pascals aren’t the common go-to in HVAC practice, and bars are far too large to capture these small pressures. That’s why inches of water column is the standard unit used to specify gas pressure operating ranges.