Abstract: In an oil fired boiler (with a combustion chamber and a burner which blows a flame into it) there is a J-shaped heat-exchange duct, built on the combustion chamber floor out of thermally ultra-conductive and non-corroding pipes and fittings. Because of the extreme rigidity and brittleness of these, our structure is designed with masonry-like constraints on duct layout: Must rest on floor--never two attachments to anything--must not rely wholly on cement for stability.The J-duct becomes hot from the radiation in combustion chamber. It serves to heat secondary air and delivers it at suitable discharge regions from which it will join the base of the entering flame.The tip of J's long leg is outside chamber and gets secondary air from blower. This leg extends into chamber through its front wall then, curving around, its short leg extends forward and ends at location next to front wall's hot face.