The Taco X-Pump Block ® (XPB) is another breakthrough in the design, control and installation of radiant systems that delivers unmatched flexibility in a single unit. It is equally effective when used with open or closed systems, barrier or non-barrier tubing and where the system heat source is a boiler or water heater. The Taco X-Pump Block combines a variable speed mixing control, a heat source Circulator, system Circulator and heat exchanger in a single unit. This combination delivers complete system isolation between the heat generation side of the system and the heat delivery side, whether radiant tubing, glycol based snowmelt, baseboard, etc.