A furnace utilizing recuperative heat exchange for preheating a combustion reactant with waste heat energy from flue gas, comprising: a combustion chamber including a combustion space enclosed by a furnace wall in which a fuel and an oxidant (103, 105) are combusted to heat solid and/or molten glass or glass-making materials or solid and/or molten metal and thereby producing flue gas; one or more burners mounted in the furnace wall adapted and configured to inject preheated fuel and/or preheated oxidant into the combustion chamber interior for combustion therein; characterised in that the furnace further comprises a duct (1, 11, 21, 31, 51, D) extending along an axis and having a first end receiving at least a portion of the flue gas produced in the combustion chamber and a second opposed end discharging the received flue gas; one or more insulating walls (3, 13, 23, 33, 43, 53, 63, IW) extending parallel to the duct axis and adjacently to an outer surface of the duct (1, 11, 21, 31, 51, D), the insulating wall (3, 13, 23, 33, 43, 53, 63, IW) being comprised of an insulating material, an non-reactive gas space (5, 15, 25, 35, 45, 65, NRG) being defined between an outer surface of the duct (1, 11, 21, 31, 51, D) and an inner surface of the insulating wall (3, 13, 23, 33, 43, 53, 63, IW); and one or more metallic pipes (7, 17, 27, 37, 47, 57, 67, MP) extending through the non-reactive gas space (5, 15, 25, 35, 45, 65, NRG), the pipes (7, 17, 27, 37, 47, 57, 67, MP) receiving the combustion oxidant or the combustion fuel and discharging the combustion oxidant or the combustion fuel after being preheated, wherein one or more portions (58, 61) of the duct (1, 11, 21, 31, 51, D) is comprised of a material having a thermal conductivity of greater than 1 W/(m·K), preferably greater than 3 W/(m·K). a combustion chamber including a combustion space enclosed by a furnace wall in which a fuel and an oxidant (103, 105) are combusted to heat solid and/or molten glass or glass-making materials or solid and/or molten metal and thereby producing flue gas; one or more burners mounted in the furnace wall adapted and configured to inject preheated fuel and/or preheated oxidant into the combustion chamber interior for combustion therein; characterised in that the furnace further comprises a duct (1, 11, 21, 31, 51, D) extending along an axis and having a first end receiving at least a portion of the flue gas produced in the combustion chamber and a second opposed end discharging the received flue gas; one or more insulating walls (3, 13, 23, 33, 43, 53, 63, IW) extending parallel to the duct axis and adjacently to an outer surface of the duct (1, 11, 21, 31, 51, D), the insulating wall (3, 13, 23, 33, 43, 53, 63, IW) being comprised of an insulating material, an non-reactive gas space (5, 15, 25, 35, 45, 65, NRG) being defined between an outer surface of the duct (1, 11, 21, 31, 51, D) and an inner surface of the insulating wall (3, 13, 23, 33, 43, 53, 63, IW); and one or more metallic pipes (7, 17, 27, 37, 47, 57, 67, MP) extending through the non-reactive gas space (5, 15, 25, 35, 45, 65, NRG), the pipes (7, 17, 27, 37, 47, 57, 67, MP) receiving the combustion oxidant or the combustion fuel and discharging the combustion oxidant or the combustion fuel after being preheated, wherein one or more portions (58, 61) of the duct (1, 11, 21, 31, 51, D) is comprised of a material having a thermal conductivity of greater than 1 W/(m·K), preferably greater than 3 W/(m·K).