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Water heater apparatus is provided with features that allow for a horizontally compact water heater installation comprising upper and lower vertically stacked electric individual water heaters served by a single electrical branch circuit. Each of the upper and lower water heaters has a water storage

Water heater apparatus is provided with features that allow for a horizontally compact water heater installation comprising upper and lower vertically stacked electric individual water heaters served by a single electrical branch circuit. Each of the upper and lower water heaters has a water storage capacity not exceeding 55 gallons, and the combined water storage capacity of the upper and lower water heaters is greater than 55 gallons. The electric heating elements of the two water heaters are non-simultaneously controlled so that at no time do the two water heaters heat water at the same time.

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1. Electric water heating apparatus comprising first and second electric water heaters each having a tank adapted to hold a quantity of water to be heated, thermal insulation arranged to insulate a portion of said tank, an electric heating structure for heating water disposed in said tank, an electr

1. Electric water heating apparatus comprising first and second electric water heaters each having a tank adapted to hold a quantity of water to be heated, thermal insulation arranged to insulate a portion of said tank, an electric heating structure for heating water disposed in said tank, an electrical control circuit for controlling said electric heating structure, and electrical wiring, the electrical control circuits of the first and second water heaters and the electrical wiring forming a control unit, wherein the control unit is arranged to the electric heating structure of the second electric water heater to be powered only if the electric heating structure of the first electric water heater is not powered, said first and second electric water heaters being in a vertically stacked end-to-end relationship in which top and bottom ends of said first and second electric water heaters, respectively, are interfittingly interlocked with one another, wherein the first and second water heaters comprise junction boxes and a vertical wiring passage extending between the junction boxes and through the thermal insulation, the vertical wiring passage containing the electrical wiring, the junction boxes being arranged to be vertically aligned when the first and second water heaters are interfittingly interlocked with one another to electrically connect said electric wiring of said first and second electric water heaters. 2. The electric water heater apparatus of claim 1 wherein: said first and second electric water heaters have identical configurations. 3. The electric water heater apparatus of claim 1 wherein: each of said first and second electric water heaters has a projection on its top end and a recess in its bottom end, with the projection of one of said first and second electric water heaters being complementarily received in the recess of the other one of said first and second electric water heaters. 4. The electric water heater apparatus of claim 3 wherein: said projections and recesses are centrally disposed respectively on said top and bottom ends of said first and second electric water heaters. 5. The electric water heater apparatus of claim 4 wherein: said projections and recesses have frustroconical configurations. 6. The electric water heater apparatus of claim 1 wherein: neither of said first and second tanks has a volume exceeding fifty five gallons, and the total volume of said first and second tanks exceeds fifty five gallons. 7. The electric water heater apparatus of claim 1 wherein each of said first and second electric water heaters has: a jacket structure outwardly circumscribing its tank and forming an insulation space between its jacket structure and its tank;an insulation material disposed in said insulation space;upper and lower electrical junction boxes respectively disposed on its top and bottom ends; anda wiring passage extending through said insulation material between said upper and lower electrical junction boxes. 8. Electric water heating apparatus comprising a plurality of electric water heaters having top and bottom ends configured to permit said plurality of electric water heaters to be vertically stacked in an end-to-end relationship in which each facing pair of said top and bottom ends interfittingly interlock with one another, each of said plurality of electric water heaters having thermal insulation arranged to insulate a portion of said tank, an electric heating structure and an electric control circuit for controlling said electric heating structure, wherein said electrical control circuits are interconnectable such that the electric heating structure of a first electric water heater of the plurality of electric water heaters is to be powered only if the electric heating structure of a second electric water heater of the plurality of water heaters is not powered; Wherein the plurality of water heaters comprise junction boxes and a vertical wiring passage extending between the junction boxes and through the thermal insulation, the vertical wiring passage containing the electrical wiring, the junction boxes being arranged to be vertically aligned when the first and second water heaters are interfittingly interlocked with one another to electrically connect said electric wiring. 9. The electric water heating apparatus of claim 8 wherein: the electric water heaters in said plurality thereof have identical configurations. 10. The electric water heating apparatus of claim 8 wherein: each of said plurality of electric water heaters has a projection on its top end and a recess on its bottom end, andwhen said plurality of electric water heaters are vertically stacked in an end-to-end relationship, the projections and recesses in each facing pair of said top and bottom ends are configured to be complementarily telescoped with one another. 11. The electric water heating apparatus of claim 10 wherein: said projections and recesses are centrally disposed respectively on said top and bottom ends of said plurality of electric water heaters. 12. The electric water heating apparatus of claim 10 wherein: said projections and recesses have frustroconical configurations. 13. The electric water heating apparatus of claim 8 wherein: each of said plurality of electric water heaters has a tank for holding water to be heated,none of said tanks of said plurality of electric water heaters has a volume exceeding fifty five gallons, andthe total tank volume of said electric water heating apparatus exceeds fifty five gallons. 14. The electric water heating apparatus of claim 8 wherein each of said plurality of electric water heaters further comprises: a tank adapted to hold a quantity of water to be heated;a jacket structure outwardly circumscribing said tank and forming an insulation space between said jacket structure and the tank;an insulation material disposed in said insulation space;upper and lower electrical junction boxes respectively disposed on said top and bottom ends of the electric water heater, anda wiring passage extending through said insulation material between said upper and lower electrical junction boxes. 15. A water heating apparatus comprising: a first water heater having: a first thermal insulation;a first tank;a first junction box;a first electric heating structure; anda first control unit connected to the first electric heating structure;a second water heater having: a second thermal insulation;a second tank;a second junction box;a second electric heating structure; anda second control unit connected to the first electric heating structure; andelectrical wiring interconnecting the first control unit and the second control unit, said electrical wiring extending through a vertical wiring passage through the first thermal insulation and the second thermal insulation, between said first junction box and said second junction box are vertically aligned when the first and second water heaters are interfittingly interlocked with one another to electrically connect said electric wiring;wherein the first control unit, second control unit, and electrical wiring are arranged such that the second electric heating structure is to be powered only if the first electric heating structure is not powered. 16. The water heating apparatus of claim 15, wherein the first control unit, second control unit, and electrical wiring are further arranged such that the second electric heating structure cannot be powered while the first electric heating structure is powered. 17. The water heating apparatus of claim 15, wherein the first tank comprises an upper end, a lower end, a projection extending upwardly from said upper end, and a recess formed in said lower end and having a configuration complementary to that of said projection. 18. The water heating apparatus of claim 17 wherein: said projection and said recess have frustroconical configurations. 19. The water heating apparatus of claim 17 wherein: said projection and said recess are centrally positioned respectively on said top and bottom ends of said electric water heater.