Another Smarter Water Heater Timer

When notes stuck to the water heater failed [Ryan] decided to whip up “the world’s most expensive 240V relay” using a servo, a real time clock and of course an Arduino. All in an attempt to save a buck or two thanks to LA’s “Time-of-Use program”.

Using a protoshield Ryan soldered up a RTC module using the DS1307 chip. On board he added some LED’s and switches including a holiday switch keep the heater off, a next cycle button when you need some hot water and to hell with the expense, and a pulsing blue LED.. for no reason at all. The board flips the mechanical switch using a servo and piano wire, simple but effective. We wonder how many days/weeks it will take for it to offset its expense?

28 thoughts on “Another Smarter Water Heater Timer

  1. The switch IS intended for continuous cycling – it’s a 24 hour timer switch!

    The cost is negligible. You are either keeping hot water hot (maintaining) or you have to heat cold water to hot (alot of energy).

    I’d be willing to bet it costs him MORE money. Pointless…

  2. @macegr Since that switch is part of a mechanical timer (and thus engineered for 2-4 switches a day) I doubt he will have much issue with wear.

    Besides, he can just replace it with an actial 240v relay when it does fail.

  3. @xFred – A little insulation work on the tank, combined with this hack ought to mitigate re-heating your concerns.

    For a small tank and infrequent bathing (not due to poor hygiene – just guessing bachelor pad or only dude and his smokin hot girlfriend in the house) this probably pays for itself. Write off tinker time as fun and it’s not a bad little project.

  4. @xFred

    Think about the simple physics. The hotter the object is, the more heat it dissipates. This is an exponential relationship. Basically since the tank is cooler it dissipates less heat. Also look at @dirtyoldman’s post for empirical evidence

  5. The savings comes from turning the water heater off during peak times, when the power company charges him more and running it during off peak times instead. Note that he mentions LA’s “Time-of-Use program”

  6. Love it.
    I turn off my water heater when I go on vacation, along with turning the A/C up to around 85F. I can get my daily kWh usage down to around 4kWh per day by doing those two things. Down from around 50kWh per day normally during the summer.
    Now I need to go buy a 240V relay and do this myself. Oh, and get a Time of Use electric rate at home too.

  7. I think the point that everyone is missing is that they may have implemented something that has been talked about often the last couple years.

    Tiered pricing on energy based on the time of day it is consumed. Agree with the merits of it or disagree with it (like me), looks like LA has started that policy.

  8. The reason I say it won’t actually save money is because the peak hours are when no one is home anyway. The water heater isn’t going to lose much heat during the day, when no one is using the hot water. Basically it’s going to run in the morning after people have taken their showers, stay hot all day, then turn on again at night after the dishwasher is run, etc. Merely having a large, insulated mass of water is already time-shifting the power usage to the off-peak hours.

  9. Is there any concern here with fostering bacteria growth like Legionella? (

    I would tend to agree w/ other posters–insulating the pipes leaving the water tank, and the tank itself will probably save more money than this device will alone.

    There is also something to be said about switching high amperage loads on/off unattended–when you’re there and you flip a switch you would notice sparks/smoke/etc… what you have there however is a system that will flip the switch when no one is around… probably it will be fine, but if there were a fire, the insurance company and fire investigators may not like seeing a home-brewed solution.

  10. Everything’s better with blue LEDs, I guess. :)

    That being said, if he’s really trying to save power (“every mW counts!”) I’d have gone with a single RGB LED as the sole status indicator, and pulsed that as a “heartbeat” indicator… but that’s just me.

  11. @hmbemis

    You are spot on.

    I doubt this device will meet “code”. It’s
    being used to control another mechanism that
    was never intended to be used in the manner
    it is here.

    Any safety agency approvals would be null
    and void in the eyes of the AHJ, and perhaps
    insurance company as well if there were indeed a
    catastrophic failure resulting in a TPR
    vent. Or perhaps an overload on the electrical
    circuit feeding the heating element (breakers
    and wiring “should be” rated for, I believe 3
    hrs of continous usage at the specified ampacity
    of the wiring/breaker – who knows if any of
    the existing electrical work was done properly
    to begin with ?).

    But, hey it’s his house. His risk – but if the
    heating element gets stuck on, and the TPR vents,
    his clean up bill. If the wiring overheats due
    to pre-existing faulty wiring and a 100% duty
    cycle due to a stuck relay, and the house burns
    down. We’re talking possible felony charges and
    no insurance coverage.

    What next ? I know! how about we wire up an
    Arduino on the gas stove ? Who cares about
    regulatory approvals ? we don’t need so stinkin’
    safety rules!

  12. If you’re really trying to save power, use a cheap red LED and blink it for 50ms or so out of every thousand, like alarm system designers have been doing since they’ve been designing with LEDs. If you want something expensive and nifty that no one will ever see because it’s in the utility closet, use a blue or RGB LED and pulse it via PWM so that your processor spends time out of sleep mode, but not doing any useful work. (No, it’s not much of a cost, but if every milliwatt counts…)

    It’s not a bad hack, as hacks go, but I’d also be a little nervous about switching 240 volts without any way to notice if there’s a problem. Don’t know if I trust my either code or circuit breakers quite that much.

  13. I love the ridiculousness of this hack. I’m really pleased the poster left that hideous frankenstien box – with 240v barely hidden behind a bit of flimsy cardboard.

    It would have been easy to take the old mechanical timer off and desgn and fit a new electronic unit. I find the bit of wire pleasing. Maybe if it was also attached to a bell-clapper so you got a chime whenever it switched?

    US wiring looks *so* dangerous to me. Almost hilariously so. I love my UK mains sockets.

  14. I love UK wiring too. I can just imagine the design meetings; “we need a system that’s safe enough and powerful enough for my four year old to do her welding from a domestic supply.”

    The only downside is that the plugs are perfectly formed for sitting on the ground pins up. They practically attract bare feet to them!

  15. i like the solution, with the little rod and stuff, it’s very neat, kinda like rube goldberesque.

    on the other hand, i wouldn’t trust my life to an arduino tripping a breaker.

    also, if the breaker is spring loaded, don’t you limit it’s speed/travel with a rod, because you will have a longer air gap arcing time between the contacts. combine that to an arduino flaking off for whatever reason, switching into an “on, off, on” loop with the breaker and you have a possible fire.

    btw might want to gfci that outlet sitting 6 inches from the washer hoses.

  16. Why he just didn’t use the timer function of the mechanical time clock is beyond me. For much less than the cost of the arduino and servo he could have purchased an electronic 240v timeclock, with exactly the same functionality. While this hack is indeed much cooler than that, it’s a more complicated way of doing something that’s being done well (and cheap) already.

    And yes, it makes a huge difference not keeping water warm. Poorly insulated water heaters can have up to 30% standby losses, and well insulated ones often see 10% standby losses. Turning the water heater off when not in use is always the right answer. I run these calculations probably 3 or 4 times a month for commercial heating plants, and it’s always the same result. Turn. It. Off.

  17. w00t? You don’t already have “off peak” hot water? It’s kinda the standard for electric hot water here…. No it does not “get” legionella. Yes insulation keeps it hot for more than 24hrs.
    Yes you can manually/automatically “boost” it during the daytime if you run out.

  18. @hmbemis

    I agree with with the various safety concerns and probable code violations with a mickey mouse setup like this. Put in a new nearly identical 240v mechanical switch for a pool pump and I wouldn’t trust his setup at all. I also live in LA county and know the tiered energy pricing is a real pain for high load appliances. Would have just purchased an UL programmable relay to keep things safe.

    If it was for something else I think it’s a clever fix, but high voltage and amperage near plumbing is something that electrical codes go into very specific detail on what is allowed.

  19. The “piece of cardboard” that 240v stuff is sitting behind inside that box is pretty much standard stuff in the commercial and industrial realms.

    The cover of the metal box is intended to keep folks out when no adjustments are necessary.

    I’m seeing a lot of comments here from folks who really don’t understand the hardware being employed.

    That being said, I have to agree that I’m not really comfortable with the servo actuator setup either.
    What’s wrong with the timer anyway?

  20. Hot water heaters have a minimum setting that you can’t override, it’s about 55 Celsius IIRC. If you maintain the temperature under that you get bacteria growth.

    Having the temperature go from room temperature and up, along with actually using it will probably keep the bacteria in check.

    I did see a report that states that you need to have the heater off for 3 days before you see any saving, although turning it off during peak rates might help.

  21. There is nothing wrong with his set up. Heck, it will even pass code. The addition of a little rod to actuate the manual actuation lever will not mean anything.

    Those timers are used for water heater all the time. They can easily handle the load assuming it was sized for the load.

    As for the cardboard, it makes a fine insulator as long as you dont get it wet. But that goes for just about anything. If you manage to get water in the box all bets are off.

  22. “I’m seeing a lot of comments here from folks who really don’t understand the hardware being employed.”

    @strider_mt2k I agree… it sounds like we have some people here flying off the handle about safety here out of paranoid ignorance.

    @MH It does NOT say that he overrode the factory thermostats/limit-switches on the water heater. Therefore there is no additional risk of an over-temperature situation from his hack.

    @ALL These Intermatic brand timers are commercial/industrial grade switches… they can absolutely handle the load and the switching cycles! The cardboard shield over the contacts is how these timers come from the factory! Notice that he’s using conduit and the proper fittings for the high voltage wiring! So you can get off his back already…

  23. Insulate, insulate, insulate include pipes right to taps. It ought to be code!
    Those Intermatic timers are a piece of plastic crap, that gear inside cooks in it’s lube and turns to pulp.

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