An on-demand pumping system makes sense if the wait for hot water is long, and the waste of ambient temperature water is significant in highly used areas such as the kitchen, bathroom or laundry area. If there are two or more hot water locations on the same trunk line that are a good distance from the hot water heater, it would be beneficial to have an on-demand pumping system. Also, if there are two or more hot water locations with similar, long wait times, it generally means they’re on separate trunk lines. If they are used often, then it would be effective to install an on-demand pumping system on each line.
Read the entire article here: When is an On-Demand Water Pumping System a Good Idea?