Abstract: A mixing and pumping module for use with an installed hydronic radiant floor heating system is described. The module comprises a primary loop for circulating water to and from a boiler; a secondary loop in valve fluid communication with said primary loop and with the manifold of a hydronic radiant floor heating system, for circulating water into and out of the manifold; and means for regulating the flows of water through the primary loop, secondary loop and manifold loop, for selective delivery of heating capacities over a wide range of heating requirements, in a configuration which is compact and readily mounted to a frame for installation on a wall of the residence or commercial building in which the system is installed.