Turning off Hot Water System at Night

Alley Cat on 20/10/2023 - 13:52

I turned off my hot water system and forgot to turn it back on (there’s a dozen switches and some of the labels are too worn to read). When I realised it was a day later when the water turned a bit cold. It got me thinking about the electricity bill. I came across this page on turning it off whenever as a strategy to save electricity. Just wondering how feasible it is. I don’t have solar or anything fancy, just a manual switch in the cupboard. Happy to install a timer thingy to make this work if it indeed pays off.

Anyone tinkering with this kind of stuff?

Home & Garden Hot Water System

Comments

  • psyren89 on 20/10/2023 - 14:04
    +58

    If you have a storage system, you should not turn it off - the water needs to be maintained at no less than 60℃ to prevent bacterial growth.

    • sumyungguy on 20/10/2023 - 14:10
      +9

      Affirming the comment by @psyren89, here's the background (applicable in Qld): https://www.qld.gov.au/health/conditions/all/prevention/legi…

      • Alley Cat on 20/10/2023 - 14:23
        +3

        I see, didn’t cross my mind about the little creatures living in my tank. Thanks.

        • AustriaBargain on 20/10/2023 - 14:41
          +2

          Same concept when sous viding your food.

          • loropy9 on 20/10/2023 - 15:09
            +1

            @AustriaBargain: Also the connected hoses/pipes may develop a leak when cooling and contracting. My plumber told me to never turn off the water heater.

            • capslock janitor on 21/10/2023 - 22:51
              -1

              @loropy9: why not ?>

            • ConsumerAffairs on 22/10/2023 - 02:48

              @loropy9: Don't know what your plumber's thinking, I guess they don't understand the concept of an instantaneous HWS. Even with a storage system, anyone who fully empties one would induce a heating and cooling cycle from the cold water entering and the burner/heater element been on. It's even 'worse' so with an instantaneous HWS with more than roughly 6-7 times the MJ of heat been applied to the heat exchanger and surrounding pipes.
              There's a minimum length of copper pipe that must be installed from any connection to the HWS to prevent that problem from occurring in the first place. Most, if not all connections within a HWS are either soldered joints or welded also aiding in preventing any possible leaks.
              As for turning off the HWS, gas storage units can be a pain in the backside to reignite when they've gone cold and as others have said, it can cause the growth of anaerobic bacteria i.e. Legionellas if you don't keep the water in the HWS above 60°C. That's why there's a 'Vacation' setting on the control dial, it's enough to keep the unit idle but it's still enough to keep the water above 60°C to prevent the bacterial growth in the system.

          • stuffandthat on 20/10/2023 - 15:14
            +2

            @AustriaBargain: Bacteria is flavour!

      • mskeggs on 20/10/2023 - 15:43
        +31

        Which is they all have tempering valves.

        • derrida derider on 21/10/2023 - 17:20
          +1

          Yep, the way it works is the water in the tank is kept well above 60℃ and diluted with cold water by the tempering valve to get it to the appropriate temperature at the tap.

    • JIMB0 on 20/10/2023 - 17:58
      +7

      Heat pump units only need to get above 65℃ once a day. This is sufficient to kill the bacteria.

    • Korban Dallas on 21/10/2023 - 21:19
      +1

      Mine set to 50 degrees. It goes to 65 I think once a week or day or something to kill the bacteria.

      Just get a heat pump. With the STCs it's pretty friggin cheap and should pay for itself in 1 to 2 years.

      Can also schedule daily / hourly for when it does and does not turn on.

      Did that during summer but in winter leave it 24/7

    • HeWhoKnows on 21/10/2023 - 22:26
      -2

      Also allowing the tank to heat and cool so much and so often will result in premature failure.
      Better to lower the temp setting on the thermostat to around 50-55 degrees.
      This is recommended anyway to prevent acidental scalding.

      Bacteria wont be a problem as you are not drinking the hot water.
      Also bactreria is not a problem with cold water.

      • JIMB0 on 22/10/2023 - 07:37
        -1

        The temperature fluctuates a lot with normal use, the bottom of the tank has cold water coming in as hot water is drawn off the top.

        Bacteria doesn't grow that well in cold water but thrives in warm water. Showering in it you are always going to ingest some.

        • HeWhoKnows on 22/10/2023 - 08:29
          -4

          Well millions of people beg to differ Jimbo baby.
          I dont see many in hospital with such bacterial infections.
          Many hot water systems are set at 50 degrees either via tempering valve or via thermostat to prevent scalding.
          Ive been doing this for decades!
          And 50 degrees is NOT WARM WATER! Try sticking your hand in it!!!!
          And yes cold water is drawn in and mixed with HOT water in the tank unless you run all the hot water out of the tank.
          In which case your tank is too small and should be upgraded.

          And its a well known fact that metal doesnt like the stresses of constant heating and cooling.

    • meong on 22/10/2023 - 13:41

      interesting, but how come most heat pump hot water systems have the recommendations (checked the manual of different brands) to set the auto-off at night around sunset and set it back just before sunrise?

      It came by default with that configuration. A few of my friends' ones are like too with different brands. Even the installer recommended that. Are they no different to the conventional electric/gas hot water systems?

      In my understanding that you don't need to maintain above 60 at all times so really as long as it can reach 60-65 again during the day it should kill the bacterias? Happy to be corrected.

  • MS Paint on 20/10/2023 - 14:10
    +2

    Depending on your electricity tariff it may well be heating your water at night time.

    • Alley Cat on 20/10/2023 - 14:38

      Single rate :(

      • bigbadboogieman on 21/10/2023 - 22:33

        Don't worry about single rate. I opted single rate when I realised the retailers were taking me for a ride with demand based tariffs.

    • ribze1 on 22/10/2023 - 14:27

      Mine is but it's still half our bill, given we have a large solar system. Knocking the house down next year so not worth replacing but kills me.

  • dust on 20/10/2023 - 14:11

    I assume you have a hot water tank? Gas or electricity? Do you have timed tariffs for electricity usage?

    • Alley Cat on 20/10/2023 - 14:23

      It’s stored electric. No timed tariffs.

  • geekcohen on 20/10/2023 - 14:14
    +1

    Sounds like you have an electric system?

    I think it would cost more to turn it off, and then back on again for it to sit there and reheat drawing power. If you had solar, it would be a different story.

    I did this with my spa. Only heat during the day when the sun is shining with my solar.

    • Alley Cat on 20/10/2023 - 14:26
      +2

      Yes electric. I was trying to figure out how much it costs or saves. I shower in the gym anyway, so the most use I get out of it is cooking.

      • deme on 20/10/2023 - 15:53
        +13

        Are you the person who stole his neighbours electricity and always used the park bbq?

      • avoidfullprice on 20/10/2023 - 17:16
        +2

        Sounds like boil your water as you need it will meet your circumstance?

        • Alley Cat on 20/10/2023 - 17:52

          Yes, it would. But I’d also like to enjoy the convenience of having a hot water system. It’s a lot easier in the morning if my tea didn’t have to share the kettle with the bathroom basin. This is more of a ‘by the way’ kind of an idea to save some $$.

      • meong on 22/10/2023 - 13:43

        Wait are you using the hot water from the tap to make tea??

        I was always advised not do this…

        • Alley Cat on 22/10/2023 - 14:03
          +1

          Lol of course not. Hot water is hugely not food-grade water. If you think I’m kidding, order a hot water unit service and see what comes out of it. Pipes also deteriorate over time, heat usually accelerates whatever chemical/physical reactions that might be taking place. Filter your drinking water always, that way you can always count on selling your kidneys one day for a Tesla.

          • meong on 22/10/2023 - 14:13

            @Alley Cat: haha i thought i read your initially comment incorrectly, all good…

  • c64 on 20/10/2023 - 14:30
    +9

    it's only going to be economical if you are going to turn it off for a long period of time. switching it off for a day or two is just going to result in you spending $$$ reheating the water. switching it off for summer if you didn't need the hot water would certainly cut your bill.

    • Alley Cat on 20/10/2023 - 14:40
      +1

      I get that. I mean, there should be a way to calculate how much electricity it uses to maintain the temperature vs heating up all the way from 20°C. Was hoping someone here had done the maths or knows how to do it.

      • JIMB0 on 20/10/2023 - 18:08
        +2

        The energy used to maintain the temperature is equal to the energy leaving the tank. The energy leaving the tank increases when the temperature difference between the hot water and the ambient air increases.

        By turning it off you'd lower the average temperature and thus the loss. Heating all that water back up would use less energy than it would of taken to maintain the temperature.

        • Alley Cat on 20/10/2023 - 18:42

          Heating all that water back up would use less energy than it would of taken to maintain the temperature.

          Thanks, it would seem to be the case as commented here as well https://www.ozbargain.com.au/comment/14448253/redir.

          Assuming the tank is well-insulated, which it seems to be given it took over a day for me to notice the difference, I doubt it costs more to heat it back up than to maintaining it. Just the health hazard that needs to be addressed.

          • JIMB0 on 20/10/2023 - 19:09
            +4

            @Alley Cat: The energy to heat it back up will always be less than maintaining it, even with poor insulation.

  • nummenoor on 20/10/2023 - 14:42
    +2

    The other way to look at it is to lower the thermostat temperature cut off. You will have cooler water but you are likely mixing that in with cold water at the tap anyway

    • valuer on 20/10/2023 - 15:38

      Yes, we did this at our previous place (we now have solar) in a cooler location and it edged the power bill down.

  • coffeeinmyveins on 20/10/2023 - 15:32
    +5

    I'll take "how to get Legionnaires' disease for $10" thanks Alex!

  • deme on 20/10/2023 - 15:51

    OP I bet you what you've done is this:

    • You've got an electric element heater on controlled load 1.
    • You've turned it off at night when CL1 kicks in.

    Now you've got no hot water.

    You are not saving any money turning your hot water off this way.

    From the website you linked:
    What’s the big user of electricity in your home?
    The sneaky culprit behind your bill shock is (very often) hot water. Hot water can make up to 30% of your home electricity bill! This is because it runs 24 hours a day – which is crazy when you think about it. Most of us take showers first thing in the morning or in the evening after getting home from work.

    This is wrong, it does not run 24/7.

    Obviously: https://en.wikipedia.org/wiki/Thermostat

    OP look at your bill for CL, CL1, CL2, Controlled Load.

    If you don't have controlled load for the heater, go get that setup, it'll save you $$$$$$$$$, it's like $0.10/kWh

    • Alley Cat on 20/10/2023 - 16:39

      There’s nothing on my bill that suggests a tiered fee structure. I’m with nectr. I’m interested in finding out about the controlled load thing tho, thanks for the heads up.

      • MS Paint on 20/10/2023 - 17:04

        Is there a separate meter for your HWS?

        • Alley Cat on 20/10/2023 - 17:53

          No, nothing fancy. Just something built in the 80s.

      • deme on 20/10/2023 - 19:07

        I'd suggest getting it setup then.

  • samcro on 20/10/2023 - 16:21

    When I lived in a unit I turned mine off after morning shower. Stayed hot all day. Then turn it back on next day,10 mins to heat up (very small tank), I'm still alive.

    • Alley Cat on 20/10/2023 - 16:40

      Did your electricity bill come down though? And by how much if it did?

      • samcro on 20/10/2023 - 17:39

        Oh yes it did. Cant remember exactly how much, but I thought it was worth it.

        • Alley Cat on 20/10/2023 - 17:45

          Cheers, that’s good enough for me :) For health reasons, it seems like you just heat it to above 60 degrees for 8 hours once in a while is sufficient to kill the bacteria build up, if any.

      • Korban Dallas on 21/10/2023 - 21:24

        Must of had a thermos hot water system

  • Devastator0 on 20/10/2023 - 16:32

    I'm curious about this, how would I go about getting my provider to have the controlled load (Hot Water Tank) run during the day? I have solar (no battery storage) so I would rather it do what it needs to do during the daylight hours.

    • Euphemistic on 20/10/2023 - 16:44
      +1

      Controlled load (typically off peak) is separately wired to run only when the power suppliers want it to. The whole idea is that you get it cheaper, but don’t get to choose when to use it.

      My electrician grandfather added an override manual switch to his off peak HWS. At the time illegal, probably still is. He installed it because during holiday times lots of extra people in the house and wanted 24/7 hot water. He was still paying for the power, just not legal to run an off peak item on standard power.

      I looked at getting a ‘solar diverter’ to heat our off peak storage hot water. It’s a device that allows your hot water to be heated when solar is generating excess. Based on the numbers it wasn’t worth spending the $900ish. Admittedly several years ago now, but since we mostly shower in the evenings and would want off peak to kick in automatically to keep the hot water hot, the sun wouldn’t have a chance to heat much anyway, just a single shower’s worth.

      The HWS is dumb, it’s the power circuit at the fuse box that allows it to heat and that could be any format you choose.

  • deme on 20/10/2023 - 19:09

    He was still paying for the power, just not legal to run an off peak item on standard power.

    This is fine, in fact some parts of the world have a boost button on the smart meter to do this.

    • MS Paint on 20/10/2023 - 22:38

      I have that in my part of the world.

  • Alley Cat on 20/10/2023 - 19:40
    +1

    Ok, I think I’ve found a possible solution here: https://www.sparkydirect.com.au/p/NLS-FDT16-16D-Single-Chann… So if I set it to turn itself off from 6pm to 6am every day except Saturday, it should in theory save a fair bit of the reheating while cooking the tank to make sure the bacteria are under control. Adding to my list of sparky tasks :)

    • MS Paint on 20/10/2023 - 22:40
      +2

      By time you pay a sparky to install that your energy savings will be next to nothing.

    • sumyungguy on 20/10/2023 - 22:40
      +1

      You may find your electric HWS is on a 30A circuit

    • LFO on 21/10/2023 - 13:02

      Double check with these timers!!

      Although they supposedly handle 16Amps they are designed to "constantly switch on and off" no more than 2.5Amps … that cryptic note says it all:

      • Incandescent lamp: 1000W

      Very tricky.

  • DoctorCalculon on 21/10/2023 - 00:14
    +1

    OP, why not invest in a heat pump HWS system?

    • Alley Cat on 21/10/2023 - 00:50

      Too small a property to justify that. More of an interest in the trade-offs because it’ll likely benefit me when I move again.

  • Sunshines bright on 21/10/2023 - 08:23

    We had an electrician install a timer so our solar now pays for the heating of the water. Showed a moderate but good enough savings

    • Blatantlie on 21/10/2023 - 22:28

      Which timer did you use? I am looking for one for to pair with my solar install and storage electric hot water heater.

      • Sunshines bright on 22/10/2023 - 11:07

        I dont have a clue as the electrician installed it. Simple switch with a tiny wheels you turn to set on an off time thats not easy to see. Attached to electric box

        • Blatantlie on 23/10/2023 - 12:03

          Oh..ok thanks anyways!

          • meong on 23/10/2023 - 16:05

            @Blatantlie: my heat pump water heater has a timer built in by using the control panel on it… check the manual, you may have it too..

            my friend's water heater even got an app for it…

  • Easyteas85 on 21/10/2023 - 08:44
    +1

    I have a large 200ltr hot water bottle electric and I put a timer on it when I installed my solar system to reduce power consumption.
    It turns on at around 10 am and off around 2pm. Being that it's such a big bottle it holds the heat enough that showers at night are still steamy hot.
    I noticed people saying you shouldn't for bacteria etc but I live in Qld and so far no issues been like that for over 2 yrs

    • Blatantlie on 21/10/2023 - 22:29

      Which timer did they use for achieving this mate?

  • Bilby s on 21/10/2023 - 09:09
    +3

    One way of saving money is to turn the water temperature down to a min acceptable level. That way you’re not maintaining a tank of super hot water that’s gets mixed with cold before you use it!

  • LFO on 21/10/2023 - 12:51

    Anyone tinkering with this kind of stuff?

    I did.

    I methodically wrote down all numbers and measurements.
    It does save about 8% … or rather it uses 8% less electricity than when permanently left on.

    It makes sense as the thermostat in the hot water system will turn on the heating element during, say, the 11pm to 5am cycle when no one will need nor use use hot water.

    It had a timer to connect to the off-peak supply from 7am to 10pm to use off-peak power whenever it was on.

    No killer bacteria and water was "boiling hot" … even at 7am.
    It was a large system (250l??) with good insulation.

    Hope this helps :-)

    • Alley Cat on 21/10/2023 - 14:36
      +1

      You are my hero, I know you exist! 8% of usage charge is not too significant but what a fascinating experiment to have conducted 😃 Thanks heaps 😇😇😇😇😇😇😇😇😇

      • LFO on 22/10/2023 - 13:19

        Cheers ;-]

    • sumyungguy on 21/10/2023 - 16:57

      You're in Qld? Storage HWS should be connected to controlled load and is only powered between 22:00 and 07:00. So you're saying you had a timer to limit the supply within that time window and saved 8%? Or your HWS is low capacity and runs on general usage with demand charges from 16:00 to 21:00?

      • LFO on 22/10/2023 - 13:28

        Not exactly that.

        Off-peak power (Controlled Load) comes on somewhere around midday (2-3hs??) and then during the night.
        I no longer have those details and these are just from memory.

        No longer using Off-peak so no longer checking.

        • LFO on 06/11/2023 - 14:06

          Cannot edit so I comment here :-]

          Substantiating my assertion about Off-peak locally available during the day:

          Today Monday 6th at around 08:21 I noticed the Off-peak switch (Ripple Control Receiver) was in the ON position.
          So we had Controlled Load Off-peak electricity available at that early hour of morning.

  • Waltervp on 21/10/2023 - 15:13

    I've had a time on my hot water fuse for years. It only heats off peak. Probably saves 10%. My new heat pump storage heater has its own timer and does the same. Makes sense to me.

  • jrvb42 on 21/10/2023 - 16:01
    +4

    It's clearly going to be cheaper to turn it off periodically, simply because the rate of heat loss when the unit/water is maintained at 60 degrees is higher than at 40 degrees.
    A cup of coffee cools from100 to 90 quicker than from 50 to 40, simply because the ambient temp is not so much lower at 50 than at 100 (50-25 less than 100-25). However, the points made about killing bacterial hold. Note that the temperature only has to hit 60 to kill the majority bacteria. Once it does, they're dead, until more are imported via the inlet valve or they reproduce

    • skittlebrau on 22/10/2023 - 12:23

      I have a solar hot water system with electric boost. I use an analog timer in my fuse box to boost once daily from 3pm to 6pm. That should be sufficient for killing bacteria right?

      My installer said allowing 3 hours for boosting was ideal and I figured by 3pm, the solar panels on the hot water system have done a lot of the work with heating up the water, so the boost is just needed to get it up to the 60 degree threshold.

      Is my reasoning sound?

  • Willywolfy on 21/10/2023 - 17:40
    +1

    I did a rough test myself although I never kept the figures however turning the hot water off over night and then back on in the morning (same times etc) I consumed more electricity.

  • altomic on 21/10/2023 - 20:29

    Im in brisbane and have a solarhart hot water system. It hasnt been connected to power for 3 years.

    The downside is that If there is 3 straight days of clouds then my water goes cold. But that has only happened once.

  • Schuy1 on 21/10/2023 - 21:03

    Here's a water heating calculator …. quite handy!

    https://www.omnicalculator.com/physics/water-heating

    • Alley Cat on 22/10/2023 - 11:57

      Thanks for that, except there’s no way of knowing how efficient the hot water unit is. I think what we really want is an efficiency rating on hot water units, and they need to have two, one for the heating, the other for the maintenance of the water temperature. It’s especially peculiar if they account for 30% of household electricity bills as some sources suggest. Switching to solar doesn’t quite resolve this.

  • capslock janitor on 21/10/2023 - 22:55

    mines gas hws. #gasgang

  • Time2Go on 22/10/2023 - 11:37

    Costed me around $800 back in 2017 for the electrician to reconnect my hot water system from a controlled load to a normal load. He also put in a timer on the circuit board so it only runs during the day when my solar is running. It saved me at least $100 on the bill per quarter.

    However, looking back, I properly should replace my old system with a heat pump system as the tank was already close to 10 years old back then. It died early this year and I replaced it with a heat pump hot water system which has a inbuild timer.

  • Hangryuman on 22/10/2023 - 13:19

    I'm a detail guy - and OTTOMH have estimated that heating our 80L peak storage (single rate) electric HWS from after two showers until hot/cycled off cost about 85c (about 45 minutes). I also guesstimated that heat loss from our stored HWS seemed to cost about $2 per day - not proven - just my impression.

    if you really want to do the frugal you could use your morning electric jug after your tea/coffee into a plastic 2L bowl mixed with cold to a comfortable temp to splash on your skin, then use a washcloth to wet, soap, and rinse off your body or face

    this morning on rising I ran the hot tap in our laundry sink (closest to the HWS tank in the laundry) like so - just turning on the hot tap into the plastic bowl starting from cold until the balance was the temp I wanted, then just dip to wet my hands, rub over/wet my face, used a bar of soap on my face (to remove the nose oil that makes my glasses slip down), then rinsed off my hands in the bowl, wiped my face to remove the soap, repeat several times, then splash the remainder to rinse off my face. Cost - about 2L of hot water. I know a guy nearby who has done this for decades. He doesn't have a working HWS.

    I also once lived on a farm without running water, just a 1000L rainwater tank that ran low in dry times - and learned to wet, wash and rinse my hair with one cup - total 250cc of water. But most of us don't need to do that - just know that it's possible.

    • Alley Cat on 22/10/2023 - 14:29

      I’m all for saving a penny but not at the loss of convenience. I grew up not having a hot water unit or a fridge in our house, so am quite familiar with how to live that life 😅 While it’s not the end of the world for me personally, it’s also not my preference. My time is a bit more valuable these days 😉 I mean if it makes sense to you, by all means go for it. When people talk about going camping, I’m always sitting there thinking I’ve clearly used up all of my quota too soon 🤣

      I have heard stories of a neighbour in his 70s who started their day by fetching hot water from the community shower to save money. He was collecting rent from three properties that he’d owned. The body corporate switched off hot water in the end lol He died a sad and lonely man, according to the stories. There is a line.

      The responses so far feel like an easy enough function that should have been implemented at the manufacturer level.

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