The unit IWC stands for inches of water column and is used to measure pressure in HVAC duct systems.

The unit IWC stands for inches of water column and is used to measure pressure in HVAC duct systems.

• A. PSI
• B. kPa
• C. IWC
• D. BAR

Answer: (C)

In HVAC ductwork, the pressures are typically quite small, so the most practical way to express them is with inches of water column. This unit directly reflects the pressure exerted by a one-inch-high column of water, which is about 0.036 psi or roughly 0.249 kPa. Using inches of water column keeps readings intuitive for balancing fans, measuring duct losses, and setting dampers, because the values fall into a convenient, familiar range for the field. Other units like PSI or BAR represent much larger pressures and don’t provide the same easy, precise scale for duct work, while kPa is correct but less commonly used in everyday HVAC practice. So the phrase described aligns with the standard HVAC convention for measuring duct pressure.

In HVAC ductwork, the pressures are typically quite small, so the most practical way to express them is with inches of water column. This unit directly reflects the pressure exerted by a one-inch-high column of water, which is about 0.036 psi or roughly 0.249 kPa. Using inches of water column keeps readings intuitive for balancing fans, measuring duct losses, and setting dampers, because the values fall into a convenient, familiar range for the field. Other units like PSI or BAR represent much larger pressures and don’t provide the same easy, precise scale for duct work, while kPa is correct but less commonly used in everyday HVAC practice. So the phrase described aligns with the standard HVAC convention for measuring duct pressure.