Indirect water heater

Corrosion-resisting apparatus for indirectly heating a domestic water supply comprising a combination of a heater for heating aqueous recirculating fluid, and a water storage tank, said heater being spaced apart and remote from said storage tank and connected to convey heat from said recirculating aqueous fluid supply to said water supply, while preventing mixing and ionic exchange between said aqueous recirculating fluid and said water supply, said apparatus comprising:

• a glass-lined storage tank for containing said water supply, said storage tank having a water inlet port, a water outlet port, and a heat-exchanging tube in said storage tank;
• a heating tube connected to convey said hot water to said heat-exchanging tube,
• said heat-exchanging tube having a plural wall comprising (a) a non-metallic outer wall and (b) a metallic inner wall,
• whereby said water supply is exposed only to said glass lining and to said non-metallic outer wall and is accordingly free of exposure to dissimilar metals and not subjected to any substantial ionic corrosion in said storage tank, wherein the inner surface of said non-metallic outer wall is in continuous contact with the outer surface of said metallic inner wall,
• a portion of one of said walls being removed between said walls to provide an elongated passageway extending between said walls, and said passageway having an exit opening leading away from said plural-wall tube, and wherein said passageway contains an elongated non-metallic material extending along between said non-metallic outer wall and said metallic inner wall and maintains substantially continuous heat transfer contact therebetween,
• said plural wall being sealed to prevent mixing of said water supply and said aqueous recirculating fluid,
• wherein said passageway is arranged lengthwise along said plural-wall heat-exchanging tube between said outer and inner walls, whereby any fluid that may leak through either wall can exit along said passageway and out of said storage tank, and
• wherein said plural-wall heat-exchanging tube is not metallurgically bonded.