A manometer measures pressure in which unit?

The correct answer is that a manometer measures pressure in inches of water column. This unit is commonly used because a manometer functions by measuring the height of a column of liquid—often water—relative to atmospheric pressure. The difference in height creates a pressure differential that can be quantified in inches of water column, which is particularly useful for low-pressure measurements.

Using inches of water column is advantageous in many HVAC and refrigeration applications, as it allows technicians to accurately assess and monitor low-pressure systems. This unit provides a clear and manageable way to express the small pressure changes that might occur in these systems.

Other options, while they are valid units of pressure in different contexts, are not typically associated with manometers. For instance, kilopascals, pounds per square inch, and bar are commonly used for measuring higher pressures and are generally used with different types of pressure gauges or sensors. A manometer's design and function are tailored to measuring small pressure differences, making inches of water column the most appropriate unit for this instrument.