RTI Pex Piping Systems offers the ThermalLock Modular Plastic Manifold for distribution and control of hydronic radiant heating systems. ThermalLock's modular design provides complete configuration flexibility. Valving is supplied on both the supply and return modules, allowing for isolation of individual zones and optional thermostatic zone control. Flow meters, supply and return temperature gauges, air vents and drain valve included. For 3/8", 1/2", 5/8" and 3/4" PEX tubing. RTI. Circle 3.