Open system vs closed? Barrier vs non-barrier tubing? Boiler vs water heater? The debate ends here. The patent pending X-Pump Block combines a variable speed mixing control, heat source circulator, system circulator, and heat exchanger into a single unit. This combination delivers complete isolation between the heat generation side of the system (boiler, water heater, etc.) and the heat delivery side of the system (radiant tubing, glycol based snowmelt, baseboard, etc.). Just four pipe connections and your installation is complete.