Furnace air circulation system

Claim 1

In combination with a furnace including a blower operable to extract air from a zone to be heated and to return said air to said zone, and a fuel burner operable to heat said air as it passes through said furnace, said burner having a vertically extending flue pipe having stack functions including the disposal of the gaseous products of combustion of said burner and the maintenance of a draft on said burner, an air circulation system comprising: a. an air jacket surrounding a substantial portion of the length of said flue pipe, and having air inlet and outlet openings adjacent the respectively opposite ends thereof, b. first conduits interconnecting the inlet opening of said jacket with a source of air to be heated by said furnace, c. a second conduit interconnecting the outlet opening of said jacket with the air inlet of said furnace, whereby said blower draws air into said furnace partially from said zone to be heated, and partially from said jacket, the air being drawn from said jacket being warmed by heat transferred thereto through the walls of said flue pipe, the furnace air intake from the zone to be heated, and said second conduit from the air outlet of said jacket, converging in a common conduit connected to the air inlet of said furnace, d. a damper disposed at said point of conduit convergence and being adjustable to vary the relative proportions of the air entering the furnace which are drawn respectively from said heated zone and from said jacket, e. automatic temperature-responsive means operable responsively to the gas temperature within said flue pipe to regulate said damper to throttle the flow of air through said jacket sufficiently to allow said flue temperature to remain sufficiently high that said flue may perform its stack functions, said automatically controlled damper always being partially open even at the extremes of its controlled movement, not completely disconnecting the furnace air intake either from the heated zone or from said jacket, and f. a normally closed additional damper disposed in each of said first conduits and operable to open responsively to draft generated by actuation of said furnace blower, each of said last-named additional dampers being equipped with means operable to adjust the degree of draft required to open said damper.