What kinds of pressures are expressed in inches of water column?

Answer 1

This is entirely up to the convenience of the user. Medical tradition has blood pressure measured in millimetres of Mercury, for this is a comfortable unit to the practitioners.

In diving, one would use ft or m as one wished.

note. In Aviation, heights are expressed in ft and thousands of ft, as an international standard; whilst distances are expressed in miles.

This mix of units ensures that the two numbers do not get confused.

Until recently, much surveying was done in ft and decimals of a ft for heights, and chains and links for horizontal distances.

Modern survey practice in SI has these both in metres.

Answer 2

The kinds of pressures expressed in inches of water column typically refer to low-pressure applications such as HVAC systems, natural gas lines, and medical equipment. It is commonly used to measure small pressure differentials or air speeds in ventilation systems.