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Community and Q&A

Electric water heater vis-à-vis time-limited water availability

has_te | Posted in Energy Efficiency and Durability on

•Given that there is available one hour of plumbed water per day;
Is it more efficient (in regards to equipment /durability v. electrical
parsimony) to turn off the heater for much of the day, turning it on
only in time to heat sufficient water for use in that hour….

•OR to simply leave it on so as to avoid possible equpment stresses and
the increased & abrupt electrical demand for that rather colder reservoir?

•The question is poorly presented but an engineering response would be
very much appreciated. I have one hour of water/day and am resource limited.



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  1. Expert Member
    Dana Dorsett | | #1

    Tank type hot water heaters are insulated, and lose a limited amount of heat to standy, but if it's left in a depeleted low-temperature state between use periods, it would lose less heat.

    Almost all tank type hot water heater heating elements are simply switched on/off, not modulated/dimmed, so the peak power loads on the equipment is the same whether the standby temperature in the tank is hot or tepid or cold.

    Letting the tank stagnate most of the time at temperatures between 30C-45C (about 85-115F) puts it at high risk of developing colonies of Legionella bacteria, which can be a fairly dangerous pathogen. It's safer/better to either keep the storage temp above 50C or below 25C. If it's a tank-type hot water heater it's probably worth the small amount extra power to keep it at 50C, and limit the standby losses by insulating all of the pipes connected to the tank (to within 2 meters of the tank, both the cold and hot side), as well as adding more insulation around the tank. The amount of insulation that makes sense depends on your costs for both electricity and insulation.

  2. has_te | | #2

    Outstanding information.
    REALLY appreciated.
    Thanks so much.
    has_te AKA jamesT/Reed Point/MT

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