Heat-saving smoke pipe attachment

Claim 1

A heat saving attachment for a central heating system including a furnace located in a relatively unheated space and having a thermostatically controlled burner operable to supply heat to a relatively heated space in response to the temperature in said heated space falling below a preset level, a chimney for venting products of combustion from said burner to the atmosphere, and a cylindrical smoke pipe extending for a given axial distance through said unheated space from said furnace to said chimney, said attachment comprising, in combination: (a) a cylindrical jacket concentrically surrounding said smoke pipe and extending between first and second ends for an axial distance less than said given distance to provide a first portion of said smoke pipe between said furnace and said jacket, a second portion surrounded by said jacket, and a third portion between said jacket and said chimney, both said smoke pipe and said attachment lying entirely within said unheated space; (b) said first and third portions of said smoke pipe being of the same diameter and said second portion being of larger diameter; (c) means substantially sealing said first and second ends of said jacket to the exterior of said smoke pipe, thereby providing an enclosed, annular chamber of substantially constant transverse dimension between the exterior of said smoke pipe and the interior of said jacket; (d) a duct communicating at one end with said chamber, adjacent one of said sealed ends thereof, and at the other end with said heated space; (e) an air intake opening through which said chamber communicates, adjacent the other of said sealed ends thereof, with said unheated space; (f) a plurality of individual, solid plates of the same annular dimensions as said chamber and supported therein at uniformly spaced intervals to lie in planes normal to the axis of the smoke pipe and jacket; (g) alternate ones of said plates each having a plurality of first openings spaced about the outer periphery and extending inwardly from said jacket for a first portion of the radial dimension of said chamber; (h) alternate plates intermediate of said ones each having a plurality of second openings spaced about the inner periphery and extending outwardly from said smoke pipe for a second portion of the radial dimension of said chamber, said second openings being axially misaligned with respect to said first openings; (i) an air circulating fan disposed to force movement of air into said intake opening, through said annular chamber and into said duct; (j) an electric motor actuable to drive said fan; (k) switch means movable to actuate and deactuate said motor; and (l) timer means operable to close said switch means for actuation of said motor in response to and a predetermined time delay after actuation of said burner and to open said switch means for deactuation of said motor in response to and a predetermined time delay after deactuation of said burner.