Abstract: A piping installation having a supply header, a return header, and a branch conduit array with parallel branch conduits is provided with a by-pass apparatus to by-pass any trapped air within the piping installation away from the branch conduit array. The by-pass apparatus is connected to the supply header at a position immediate to the supply header end of the downstream-most branch conduit, and to the return header. The by-pass apparatus has a by-pass conduit and an adapter. The by-pass conduit has a length and an inside diameter that presents substantially more resistance to the flow of fluid than to the flow of air. In addition, the length of the by-pass conduit allows the supply header to be properly spaced from the return header so as to minimize thermal interference. An adapter is provided on each end of the by-pass conduit and facilitates the connection of the by-pass conduit to the respective header.

Abstract: A fresh air ventilator system for a building or the like having a conditioned air plenum and a return air aperture communicating interiorly of the building, respectively, for circulation of conditioned air within the building, characterized by a ventilator unit disposed in a weather-proof cabinet on a sealing roof curb on the roof of the building. The ventilator unit includes a fresh air inlet adapted to admit fresh air and exclude precipitation and having a fresh air damper for controlling the quantity of fresh air from zero to the maximum; an air circulating blower suitably connected to effect circulation of air through the building; an exhaust means for at least periodically exhausting a portion of the return air; a proportioning damper disposed at the return air aperture for proportioning the amount of return air, from zero to the maximum, fed to the circulating blower; and air conditioning means for conditioning the air to be circulated.