Glass-coated water heater constructed of multiple metals

Abstract

A water heater including a tank for holding heated water made at least partially of mild steel, a heat exchanger for heating water made at least partially of stainless steel, an inlet to add water to the tank, an outlet to withdraw water from the tank, and an anode connected to the tank. An inner water-facing surface of the tank is coated at least partially with a protective coating, and a water-facing surface of the heat exchanger is coated at least partially with a protective coating.

What is claimed is: 
     
         1 . A water heater comprising:
 a tank constructed at least partially of a mild steel and adapted to hold water to be heated;   a heat exchanger constructed at least partially of a stainless steel, adapted to heat the water in the tank;   an inlet to add the water to the tank;   an outlet to withdraw the water from the tank; and   an anode assembly electrically connected to the tank,   wherein an inner water-facing surface of the tank is at least partially coated with a first protective coating;   wherein a water-facing surface of the heat exchanger is at least partially coated with a second protective coating.   
     
     
         2 . The water heater of  claim 1 , wherein the first protective coating and the second protective coating comprise glass. 
     
     
         3 . The water heater of  claim 1 , wherein the first protective coating comprises epoxy. 
     
     
         4 . The water heater of  claim 1 , wherein the heat exchanger is constructed at least partially of a ferritic or a duplex stainless steel. 
     
     
         5 . The water heater of  claim 4 , wherein the surface of the heat exchanger is at least partially coated with a white metal blast with 25-50 grit or 50-80 grit arranged between the glass coating and the ferritic or the duplex stainless steel. 
     
     
         6 . The water heat of  claim 1 , wherein the heat exchanger is constructed at least partially of an austenitic stainless steel. 
     
     
         7 . The water heater of  claim 6 , wherein the surface of the heat exchanger is at least partially coated with a white metal blast with 25-50 grit or 50-80 grit arranged between the glass coating and the austenitic stainless steel. 
     
     
         8 . The water heater of  claim 1 , wherein the anode assembly is a sacrificial anode assembly or a powered anode assembly. 
     
     
         9 . The water heater of  claim 1 , further comprising a powered anode supplying current density of at least about 40 mA/m 2 . 
     
     
         10 . The water heater of  claim 1 , further comprising a constant current anode supplying current density of greater than or equal to about 100 mA/m 2 . 
     
     
         11 . The water heater of  claim 1 , wherein the stainless steel comprises 304L stainless steel. 
     
     
         12 . The water heater of  claim 1 , wherein the stainless steel comprises at least one high heat flux region on the heat exchanger. 
     
     
         13 . The water heat of  claim 1  further comprising a transition sensitive zone of the heat exchanger and a burner, wherein the stainless steel comprises one or more of the following regions on the heat exchanger: (i) an area that is within line of sight contact with the burner, (ii) a transition location within the transition sensitive zone, (iii) a baffle within the transition sensitive zone, (iv) an elbow or a bend within the transition sensitive zone, and (v) a location within about 3 burner lengths from the burner. 
     
     
         14 . The water heater of  claim 1 , wherein the stainless steel comprises at least one high heat flux region on the heat exchanger having a surface temperature during burner operation greater than or equal to about 30° F. higher than the water temperature. 
     
     
         15 . The water heater of  claim 1 , wherein the stainless steel comprises at least one high heat flux region on the heat exchanger, wherein the mild steel and the at least one high heat flux region comprised of the stainless steel are separated by a region of reduced heat flux by a distance of about 3 inches to about 6 inches. 
     
     
         16 . The water heater of  claim 1 , wherein the stainless steel comprises at least one high heat flux region on the heat exchanger, wherein the mild steel comprises at least one region on the tank less than about 3 inches from the at least one high heat flux region comprised of the stainless steel, wherein the at least one region comprised of mild steel is thicker than a region of the tank comprised of mild steel greater than about 3 inches from the at least one high heat flux region comprised of stainless steel. 
     
     
         17 . The water heater of  claim 1 , wherein the coated stainless steel comprises at least one high heat flux region on the heat exchanger, wherein the anode assembly provides increased corrosion resistance of the at least one high heat flux region comprised of the coated stainless steel or wherein of the anode assembly provides increased corrosion resistance of at least one region comprised of mild steel less than about 3 inches from the at least one high heat flux region comprised of coated stainless steel. 
     
     
         18 . The water heater of  claim 1 , further comprising high heat flux regions constructed of mild steel and non-high heat flux regions constructed of stainless steel. 
     
     
         19 . The water heater of  claim 1 , wherein high heat flux regions do not comprise mild steel. 
     
     
         20 . The water heater of  claim 1 , wherein condensing areas, when present, do not comprise a mild/stainless steel interface.