Abstract: The present double walled grease duct includes a tubular outer shell surrounding a tubular inner liner, wherein a spacer is positioned perpendicular to the walls of the outer shell and the inner liner. The spacer can include a plurality of vertical metal strips extend from a top edge of the spacer to the bottom edge of the spacer, wherein the top edge of the spacer contacts the walls of the outer shell and wherein the bottom edge of the spacer contacts the walls of the inner liner. The metal strips resist the different rates of thermal expansion between the outer shell and inner liner ultimately preventing the collapse of the inner liner under pressure from thermal expansion.

Abstract: The present double walled grease duct includes a tubular outer shell surrounding a tubular inner liner, wherein a spacer is positioned perpendicular to the walls of the outer shell and the inner liner. The spacer can include a plurality of vertical metal strips extend from a top edge of the spacer to the bottom edge of the spacer, wherein the top edge of the spacer contacts the walls of the outer shell and wherein the bottom edge of the spacer contacts the walls of the inner liner. The metal strips resist the different rates of thermal expansion between the outer shell and inner liner ultimately preventing the collapse of the inner liner under pressure from thermal expansion.

Abstract: A double-walled chimney comprising inner and outer concentric pipes providing an annular insulating space between them is made up of coaxial end-to-end inner pipes surrounded by concentric, coaxial outer pipes. The inner pipes meet at a junction transverse or radial to the basic axis and are interconnected by an inner, annular ring. The outer pipes stop axially short of meeting so that an annular gap exists that exposes or opens to the junction of the inner pipes. Circumferentially spaced apart spacers are secured to the inner ring and project outwardly as well as axially in opposite directions to engage the outer pipes to keep the latter spaced outwardly from the inner pipes and further to stabilize the outer pipes axially. An outer band connects the outer pipes together and functions also to close the gap between the outer pipes and thus to complete the insulating space at the outer pipe gap.