Pre-mix fuel fired appliances having improved heat exchange interfaces

Abstract

Pre-mix fuel fired appliances having improved heat exchange interfaces are disclosed. Embodiments may include a fuel-fired heating appliance having a burner, a first housing comprising an outlet, the first housing disposed adjacent the burner and configured to receive combustion gas from combustion at the burner, and a heat exchanger having a heat exchanger tube with a first bend and a second bend, and an inlet disposed adjacent the outlet of the first housing. The heat exchanger may be configured to receive combustion gas from the first housing. The appliance may include a blower configured to direct air toward the first bend of the heat exchanger tube, and a heat transfer insert disposed at least partially in the heat exchanger tube, the heat transfer insert having a first end disposed in the first housing, and a second end disposed adjacent to the first bend of the heat exchanger tube.

That which is claimed is: 
     
         1 . A fuel-fired heating appliance comprising:
 a burner;   a first housing comprising an outlet, the first housing disposed adjacent the burner and configured to receive combustion gas from combustion at the burner;   a heat exchanger comprising a heat exchanger tube having a first bend and a second bend, and an inlet disposed adjacent the outlet of the first housing, the heat exchanger configured to receive combustion gas from the first housing, wherein heat from the combustion gas is conducted through the heat exchanger and transferred to air adjacent to an exterior of the heat exchanger;   a blower configured to direct air toward the first bend of the heat exchanger tube; and   a heat transfer insert disposed at least partially in the heat exchanger tube, the heat transfer insert comprising a first end disposed in the first housing, and a second end disposed adjacent to the first bend of the heat exchanger tube.   
     
     
         2 . The fuel-fired heating appliance of  claim 1 , wherein the heat transfer insert is positioned such that the combustion gas flows over the heat transfer insert when the combustion gas flows through the outlet of the first housing and the inlet of the heat exchanger. 
     
     
         3 . The fuel-fired heating appliance of  claim 2 , further comprising:
 an interface insert disposed at the outlet of the first housing, and configured to separate the outlet of the first housing from the inlet of the heat exchanger;   wherein the heat transfer insert defines a thermal resistance that inhibits heat transfer from the combustion gas to the interface insert.   
     
     
         4 . The fuel-fired heating appliance of  claim 1 , wherein the heat transfer insert extends across an interface between the outlet of the first housing and the inlet of the heat exchanger. 
     
     
         5 . The fuel-fired heating appliance of  claim 1 , wherein the heat exchanger tube has a first linear portion adjacent to the first bend, the first linear portion having a first length; and
 wherein the heat transfer insert has a second length equal to or greater than the first length.   
     
     
         6 . The fuel-fired heating appliance of  claim 1 , wherein the heat transfer insert has a material composition so that the heat transfer insert provides sufficient thermal resistance to heat transfer between the combustion gas as the combustion gas flows through the outlet of the first housing and the inlet of the heat exchanger to maintain a stress at the inlet below a yield stress of the inlet. 
     
     
         7 . The fuel-fired heating appliance of  claim 1 , wherein the blower does not direct air toward the outlet of the first housing or the second bend of the heat exchanger tube. 
     
     
         8 . The fuel-fired heating appliance of  claim 1 , wherein the heat transfer insert has a length of between 13 inches and 14 inches. 
     
     
         9 . The fuel-fired heating appliance of  claim 1 , wherein the fuel-fired heating appliance is an ultra-low NOx gas furnace. 
     
     
         10 . The fuel-fired heating appliance of  claim 1 , wherein the blower is oriented to direct air toward a rear end of the heat exchanger. 
     
     
         11 . An ultra-low NOx gas furnace comprising:
 a burner;   a first housing comprising an outlet, the first housing disposed adjacent the burner and configured to receive combustion gas from combustion at the burner;   a heat exchanger comprising a heat exchanger tube having a first bend and a second bend, and an inlet disposed adjacent the outlet of the first housing, the heat exchanger configured to receive combustion gas from the first housing, wherein heat from the combustion gas is conducted through the heat exchanger and transferred to air adjacent to an exterior of the heat exchanger;   a blower configured to direct air toward the first bend of the heat exchanger tube; and   a heat transfer insert disposed at least partially in the heat exchanger tube, the heat transfer insert comprising a first end disposed in the first housing, and a second end disposed adjacent to the first bend of the heat exchanger tube.   
     
     
         12 . The ultra-low NOx gas furnace of  claim 11 , wherein the heat transfer insert is positioned such that the combustion gas flows over the heat transfer insert when the combustion gas flows through the outlet of the first housing and the inlet of the heat exchanger. 
     
     
         13 . The ultra-low NOx gas furnace of  claim 12 , further comprising:
 an interface insert disposed at the outlet of the first housing, and configured to separate the outlet of the first housing from the inlet of the heat exchanger;   wherein the heat transfer insert defines a thermal resistance that inhibits heat transfer from the combustion gas to the interface insert.   
     
     
         14 . The ultra-low NOx gas furnace of  claim 11 , wherein the heat transfer insert extends across an interface between the outlet of the first housing and the inlet of the heat exchanger. 
     
     
         15 . The ultra-low NOx gas furnace of  claim 11 , wherein the heat exchanger tube has a first linear portion adjacent to the first bend, the first linear portion having a first length; and
 wherein the heat transfer insert has a second length equal to or greater than the first length.   
     
     
         16 . The ultra-low NOx gas furnace of  claim 11 , wherein the heat transfer insert has a material composition so that the heat transfer insert provides sufficient thermal resistance to heat transfer between the combustion gas as the combustion gas flows through the outlet of the first housing and the inlet of the heat exchanger to maintain a stress at the inlet below a yield stress of the inlet. 
     
     
         17 . The fuel-fired heating appliance of  claim 11 , wherein the blower does not direct air toward the outlet of the first housing or the second bend of the heat exchanger tube. 
     
     
         18 . The fuel-fired heating appliance of  claim 11 , wherein the heat transfer insert has a length of between 13 inches and 14 inches. 
     
     
         19 . A gas furnace comprising:
 a burner;   a first housing comprising an outlet, the first housing disposed adjacent the burner and configured to receive combustion gas from combustion at the burner;   a heat exchanger comprising a heat exchanger tube having a first bend and a second bend, and an inlet disposed adjacent the outlet of the first housing, the heat exchanger configured to receive combustion gas from the first housing, wherein heat from the combustion gas is conducted through the heat exchanger and transferred to air adjacent to an exterior of the heat exchanger;   a blower configured to direct air toward the first bend of the heat exchanger tube; and   a heat transfer insert disposed at least partially in the heat exchanger tube, the heat transfer insert comprising a first end disposed in the first housing, and a second end disposed adjacent to the first bend of the heat exchanger tube, wherein the heat transfer insert is positioned such that the combustion gas flows over the heat transfer insert when the combustion gas flows through the outlet of the first housing and the inlet of the heat exchanger.   
     
     
         20 . The gas furnace of  claim 19 , further comprising:
 an interface insert disposed at the outlet of the first housing, and configured to separate the outlet of the first housing from the inlet of the heat exchanger;   wherein the heat transfer insert defines a thermal resistance that inhibits heat transfer from the combustion gas to the interface insert.