A boiler loop system including a primary-secondary piping loop interface apparatus including a flow diversion device, and a drain valve, and a drain port in branches from a circumferential sidewall. In an embodiment, supply branch piping and return branch piping connect the primary-secondary piping loop interface apparatus to a boiler and provide attachment points for auxiliary plumbing equipment. In an embodiment, the boiler loop is integrated into the primary loop.

Gas flow control valves comprising a valve housing including a cylindrical interior passage, and a housing opening extending from the interior passage through the housing. The gas flow control valve further comprises a cylindrical rotary valve element including a sidewall, and a rotary valve element opening extending through the sidewall. The valve element is rotatably received within the interior passage of the valve housing, such that the housing opening may be selectively aligned with the rotary valve element opening, and an area of overlap of the housing opening and the valve element opening may be varied by rotating the valve element within the interior passage of the valve housing.

A boiler loop system including a primary-secondary piping loop interface apparatus including a flow diversion device, and a drain valve, and a drain port in branches from a circumferential sidewall. In an embodiment, supply branch piping and return branch piping connect the primary-secondary piping loop interface apparatus to a boiler and provide attachment points for auxiliary plumbing equipment. In an embodiment, the boiler loop is integrated into the primary loop.