To determine the flow rate of a hot water recirculation pump for a domestic water supply, measuring the flow rate is the most accurate method. If selecting a new pump, understanding the specific requirements of the system is crucial. Users discussed brands like Grundfos and Taco as potential options for pumps. It’s important to consider factors such as pipe size and distance from the water heater when estimating flow rates. Ultimately, precise measurement or manufacturer specifications will guide the selection process effectively.