Can I install my new small under-counter Bosch ES4 four-gallon electric hot water tank on its side rather than vertically? PR valve would be on the side instead of on top. I’ve got a clearance problem. Thank you!

  • 1
    Most counters/cupboards have their floor raise up 3 or 4 inches from the room floor. It might be possible to cut out a section of that floor to get enough room.
    – crip659
    Nov 20, 2023 at 15:41
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    Manual says vertically but it is a sealed 4 gallon tank. I don’t know why it can’t?
    – Tom
    Nov 20, 2023 at 15:42
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    Neither do we. Are you asking us to give you permission to void your warranty and create a potentially dangerous situation? Buy a unit that suits your needs or make other accommodations.
    – isherwood
    Nov 20, 2023 at 15:47
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    – isherwood
    Nov 20, 2023 at 15:49
  • It would be interesting to know why you have a clearance problem. Typical bottom cabinets have room for this thing. Can you add a picture? Would putting it in an adjacent cabinet solve the problem?
    – jay613
    Nov 20, 2023 at 16:09

3 Answers 3


No. The installation manual for the ES 2.5, 4 and 8 says "Horizontal installation - ES8 Model Only". So no, you can't do that with the ES4.

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    And even the ES8, when installed sideways so the water pipes come out the side, requires the PRV to be moved to the new top side so it remains on top.
    – jay613
    Nov 20, 2023 at 16:08

Nope, and there's a Technology Connections for this.

The whole system is built around gravity, that's how it separates the heated water from the cold. If you misorient it, that won't work, and water temperature will be spotty.

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    Does that apply even to the little (e.g., 4 gallon) heaters? Nov 20, 2023 at 16:59
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    I like TC vids too, but this one's not near tall enough to support a vertical temp gradient like traditional water heaters.
    – dandavis
    Nov 20, 2023 at 20:43
  • @dandavis I've seen some pretty squat water heaters. Have a 4-gallon too, and it seems to work. Nov 23, 2023 at 1:29

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The wall mounting plate holds the water heater with the two metal protrusions which go into corresponding holes in the back. Since the holes are only in one positions, there's no way to change the mounting.

Even if you managed to somehow mount it, as the others said, it still wouldn't work. The hot water outlet needs to be on top and the cold water intake needs to be on the bottom. This means the vertical model has an internal pipe to send cold water to the bottom, while th horizontal doesn't, hot and cold water fittings are simply spaced more.

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