Domestic Hot Water Systems in most multifamily buildings, hotels, dormitories and senior care facilities generally employ one of three types of return or recirculation system.

The first option is to have no recirculation piping at all. This is most often found on the smaller size facilities, where there are short runs (distance) between the supply source (boiler or heater) and the farthest usage point (tap).

The second option is a gravity return system (thermosiphon circulation). The monitoring data indicate that these systems have a very low water flow, ranging from 0 to 0.5 gpm.

The third option is a forced recirculation system. These systems employ a small pump to keep water flowing, thus avoiding stagnation and the need for residents to run the tap for long periods (particularly on upper floors) to receive sufficiently hot water. The pumps are either configured to run continuously or may be cycled on and off, activated by an aqua-stat or water flow.

Although recirculation pumps should be sized to meet each individual building's requirements, common practice is "one size fits all".

The following illustration is an example of a forced recirculation loop for multifamily buildings, hotels, dormitories and senior care facilities domestic hot water system.