When measuring the maximum height of a testable backflow device, to what should the measurement be taken?

The measurement of the maximum height of a testable backflow device should indeed be taken from the outlet of the test parts. This is because the outlet represents the discharge point where potential backflow issues could arise and therefore is critical in assessing the overall height and functioning of the device in relation to its installation and operational environment.

This measurement helps ensure that the device is installed correctly and complies with applicable codes and regulations, which often dictate that certain clearances are maintained above this point to prevent contamination of the potable water supply. Taking the measurement from the outlet of the test parts provides a definitive reference point for determining whether the backflow prevention device is positioned correctly in the system, ensuring it functions effectively in protecting the water supply.