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I live in Europe and have a gas furnace that heats the water in my hot water storage tank. I would like to add a backup electrical heating element to the tank that I can turn on if our furnace ever breaks, if there's a disruption to the gas supply, etc.

I believe this port pictured below could be a G 6/4” pipe thread which could accept a standard electrical heating element.

To proceed, I imagine I would need to shut off the furnace, shut off the water supply, drain the tank, open the port, confirm it's 6/4" pipe thread, screw in the new electrical heating element, refill the tank, and then turn everything back on. Does that sound right? Are there other considerations I'm missing?

Edit: I located the manual

enter image description here

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    You need a thermostat as well as a heating element.
    – Ecnerwal
    Oct 29, 2021 at 12:41
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    I think many immersion heaters made for residential backup have integrated thermostats, and the storage tank probably does not have a second port for a separate thermostat. The documentation would be very useful in this regard!
    – jay613
    Oct 29, 2021 at 12:47
  • Thanks for posting the manual. Nice system. Do you have gas and solar like in the manual? If so why do you need a third source? And I see the heater port is on the side, so contrary to my answer you'll have to mostly drain it.
    – jay613
    Oct 29, 2021 at 16:55
  • Gas companies are very reluctant to allow residential gas interruptions, because turning gas back on is a nightmare. It's the pilot lights. They don't re-light themselves, and an unlit pilot will slowly fill the house with gas until kaboom. SO they must turn off the main or neighborhood valve, turn off each house, restore gas service, then contact each resident and get a time when their worker can enter, find all the gas appliances, and confirm the pilots were re-lit. Half the customers want to be front of the queue, and the other half you can't even reach. A few DIY, botch it and kaboom.
    – Harper - Reinstate Monica
    Oct 29, 2021 at 21:06

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  1. You need to find the owners manual for the tank to ensure it is compatible with a backup immersion heater, and what maximum power heater you can use, and to read about proper grounding and corrosion protection.

  2. Usually the immersion port would be at the top of the tank so you don't have to drain it. If it's connected to utility pressure you only need to turn that off and drain all the pipes above the tank in your home. If it's fed by your own cold storage tank you need to drain that and everything else that is higher than this hot storage tank but not the hot tank itself. Maybe there is a shutoff valve near this tank on both the inlet and outlet, then you don't need to drain anything. The tank doesn't have to be empty to shove a heater in through the top. Read the manual to make sure all the details of what you do are safe.

  3. If the furnace heats this tank through a secondary coil you don't have to shut that off, though you probably want the tank to cool down so you can test your backup heater. If the furnace heats the hot water directly then yes you need to shut it off of course so it isn't pumping water through the tank while you are working on it.

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