Heat exchanger for recovering waste heat

Claim 1

In combination with a heating device having a heat supply duct for carrying heated air to a space to be heated, and an exhaust stack for carrying exhaust gases to a flue, said combination comprising, a self contained heat exchanger unit separate and apart from the heating device, said heat exchanger unit including an outer housing operably interconnected between the exhaust stack and flue for conducting the exhaust gases therebetween, a heat exchanger component having a main body within said housing and having inlet and outlet elements extending to the exterior, the inlet element having an opening at the exterior at the bottom and the unit including means for impelling air from the exterior, ambient to the unit, through the inlet opening and into and upwardly through the heat exchanger component, the heat exchanger component including a spiral member turned about a longitudinal axis extending between the exhaust stack and flue and having a substantial dimension along that axis and in radial direction, the spiral member including opposed walls defining a spiral passage therebetween having an outer end communicating with the inlet element and an inner end forming a central space at the axis of small radial dimension communicating with the outlet element, said outlet element leading upwardly from the unit and having an elevated portion communicating with the heat supply duct, and control means for controlling said heating device which itself includes heat sensing means in said elevated portion of said outlet element and operable for so controlling said heating device according to the temperature of the air in said elevated portion, said walls also defining spaces between the adjacent turns of the spiral passage extending axially through the component for carrying exhaust gases therethrough and thereby through the component, and the housing and component being so selectively dimensioned as to provide an additional space therebetween nearly around the component and opening at both ends axially.