Heat exchanger and water heater incorporating same

Abstract

A heat exchanger ( 10 ) for a water heater. The heat exchanger ( 10 ) has a first part ( 12 ) and second part ( 14 ). A heat exchanging medium flows through the first and second parts. The majority of the length of the first part ( 12 ) is in direct heat exchanging contact with a substance to be heated and the majority of the length of the second part ( 14 ) is encased in an insulative material or substantially thermally isolated from the substance to be heated.

1 - 22 . (canceled) 
     
     
         23 . A heat exchanger for a water heater, the heat exchanger including:
 a first part through which a heat exchanging medium flows; and   a second part through which the heat exchanging medium flows,   wherein a majority of the length of the first part is in direct heat exchanging contact with a substance to be heated and a majority of the length of the second part is encased in an insulative material.   
     
     
         24 . A heat exchanger as claimed in  claim 23 , wherein, in the first part, the heat exchanging medium generally flows in a first direction and, in the second part, the heat exchanging medium generally flows in a second direction, generally opposite to the first direction. 
     
     
         25 . A heat exchanger as claimed in  claim 23 , wherein substantially all of the length of the second part is encased in an insulative material. 
     
     
         26 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger first part is a hollow cylinder and the second part is generally straight tube 
     
     
         27 . A heat exchanger as claimed in  claim 26 , wherein the hollow cylinder is formed from coiled tube. 
     
     
         28 . A heat exchanger as claimed in  claim 26 , wherein the second part is positioned within the hollow cylinder. 
     
     
         29 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger first part is a generally straight tube and the second part is a generally straight tube. 
     
     
         30 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger first part has heat exchanging fins externally attached thereto. 
     
     
         31 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger first part includes an inlet. 
     
     
         32 . A heat exchanger as claimed in  claim 31 , wherein the inlet has a length of insulative material substantially adjacent thereto. 
     
     
         33 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger second part includes an outlet. 
     
     
         34 . A heat exchanger as claimed in  claim 33 , wherein the outlet has a length of insulative material substantially adjacent thereto. 
     
     
         35 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger is generally in the shape of an elongate U. 
     
     
         36 . A heat exchanger as claimed in  claim 23 , wherein the heat exchanger includes a third part joining a downstream end of the first part to an upstream end of the second part. 
     
     
         37 . A heat exchanger as claimed in  claim 23 , wherein the insulative material is an air gap within an external cover. 
     
     
         38 . A heat exchanger as claimed in  claim 37 , wherein the external cover is a cylindrical cover of like material to the heat exchanger material. 
     
     
         39 . A heat exchanger for a water heater, the heat exchanger including:
 a first part through which a heat exchanging medium flows; and   a second part through which the heat exchanging medium flows,   wherein a majority of the length of the first part is in direct heat exchanging contact with a substance to be heated and a majority of the length of the second part is substantially thermally isolated from the substance to be heated.   
     
     
         40 . A heat exchanger as claimed in  claim 39 , wherein substantially all of the length of the second part is substantially thermally isolated from the substance to be heated. 
     
     
         41 . A heat exchanger as claimed in  claim 39 , wherein the insulative material is a solid or semi solid insulative material applied to an exterior surface of the second part. 
     
     
         42 . A heat exchanger as claimed in  claim 41 , wherein the insulative material is a close coupled polymer that has a low heat transfer coefficient compared to the heat exchanger material. 
     
     
         43 . A water heater including:
 a tank adapted for containing water;   a heat exchanger within the tank and including a first part through which a heat exchanging medium generally flows in a first direction and a second part in which the heat exchanging medium generally flows in a second direction, generally opposite to the first direction,   wherein a majority of the length of the first part is in direct heat exchanging contact with the water in the tank and a majority of the length of the second part is encased in an insulative material.   
     
     
         44 . A water heater including:
 a tank adapted for containing water;   a heat exchanger within the tank and including a first part through which a heat exchanging medium generally flows in a first direction and a second part in which the heat exchanging medium generally flows in a second direction, generally opposite to the first direction,   wherein a majority of the length of the first part is in direct heat exchanging contact with the water in the tank and a majority of the length of the second part is substantially thermally isolated from the substance to be heated.