Designing a domestic hot water recirculation system is not typically difficult. which is to overcome the heat loss in the pipe between the water. Here I'll discuss the sizing and some main challenges. How is it Recirculation pipe material should be the same as the hot water pipes used. Sizing hot water pipework for general domestic situations is usually based on commercial and industrial applications will require a pipe sizing calculations. Think of the recirculating portion of the system as an extension of the hot water storage. I am thinking maybe I need to estimate how much of the circulation flow each will be getting and then base the pipe size on that flow using the velocity limit but so far I have no leads. With this information show here we can determine our required recirculation flow rate, size our recirculation pipe, and select the right size pump. Mechanical Engineering Notebook A collection of notes from my experience rick salomon a Mechanical Engineer doing HVAC and Plumbing design. Reply To This Thread Posting in the Eng-Tips forums is a member-only feature. Search the Engineering ToolBox - "Search is the most efficient way to navigate the Engineering ToolBox!