The piping shown in Figure 1 is a partial representation of an actual installation. The portion of the system shown on the right side supplies 14 independently controlled zones, with 14 circulators each having a nominal 200-watt power input. There’s another circulator (P1) piped in above the zone circulators. There’s also a crossover pipe between the supply and return sides of this piping assembly. The occupants of the large home where this system is installed state that when only 2 or 3 zones are operating, comfort is fine. However, as more zone circulators turn on, there’s less and less heat output from all the active zones. Can you diagnose why this is happening, and suggest alternate methods for constructing this portion of the system?