On what basis would you specify a heating circulator?

The specification of a heating circulator is primarily based on the flow rate measured in US gallons per minute and the feet head differential. This is crucial because circulators must move water through the heating system efficiently while overcoming resistance from the piping and components in that system.

The flow rate indicates how much water needs to be circulated to maintain the desired temperature in the heating system, while the feet head differential refers to the height difference that the circulator must work against as it moves the water. This includes overcoming friction losses in the pipes, as well as the gravitational lift required if the system has vertical components. Understanding these parameters is essential for ensuring that the circulator can effectively deliver hot water where it's needed throughout the system, maintaining comfort and efficiency.

Other aspects like pipe diameter and length, or heating load, are important in system design but do not alone define the operational capabilities needed from the circulator itself. Temperature difference and flow rate are related but don’t directly address the operational parameters specific to the circulator. Therefore, focusing on the flow rate in gallons per minute alongside the associated head pressure is the correct approach when specifying a heating circulator.