Seasonality of kWh used for hot water heating

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During the months when my radiator heating tends to be zero, my hot water and cooking usage are as follows in kWh: May 635, June 473, July 359, August 381 and September 639.

I presume that in the colder months, the hot water will take more kWh to heat. Is there a rule of thumb that I can use to estimate my hot water usage during the months when I also use central heating? 
I have osteoarthritis in my hands so I speak my messages into a microphone using Dragon. Some people make "typos" but I often make "speakos".
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  • sandy700
    sandy700 Posts: 175 Forumite
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    I use, on average, 11 kWh a day for hot water and cooking and have not noticed any noticeable difference in consumption between the colder months and the warmer months but then I can't separate hot water only from heating radiators.

    Heating and hot water is from a combi.
  • wild666
    wild666 Posts: 2,126 Forumite
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    My monthly usage of gas is around £4.20 with £8.33 SC. My combi boiler doesn't seem to have a function for stopping the preheating of water it's a Valiant ecotech pro 28.
    If you can turn off a function to preheat water do it and lower temperatures to 50 degrees for water and 55 degrees for heating.
    Someone please tell me what money is
  • frugalmacdugal
    frugalmacdugal Posts: 10,077 Forumite
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    Hi,
    remember that over the winter months the water that you are heating is colder, so that's another consideration.
  • getmore4less
    getmore4less Posts: 46,882 Forumite
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    During the months when my radiator heating tends to be zero, my hot water and cooking usage are as follows in kWh: May 635, June 473, July 359, August 381 and September 639.

    I presume that in the colder months, the hot water will take more kWh to heat. Is there a rule of thumb that I can use to estimate my hot water usage during the months when I also use central heating? 
    I have been doing some analysis of electric,  the most significant reductions in use are going on holiday.

    if your heating was definitely off for those 5 months can you identify why the 2 higher months are over 75% higher than July.
  • Xbigman
    Xbigman Posts: 3,887 Forumite
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    Do you cook less in the summer, or maybe go out more? Less cooking means less hot water for washing up. 


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  • k_man
    k_man Posts: 1,636 Forumite
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    edited 8 October 2022 at 2:19PM
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    Hi,
    remember that over the winter months the water that you are heating is colder, so that's another consideration.
    Mains water temperature only varies by a few degrees during the year (there was a similar thread last winter),  so this will only make a few % difference.
    (Corrected)

    There will be more pipe heat loss between boiler and taps/tank if the ambient temperature is colder, but it may even be warmer if the heating is on.

    There also may actually be a reduction in hot water energy use, if the water is heated while the boiler is already heating for CH, so already up to temp.

    I think the biggest factor is change in hot water use in the winter (longer hotter showers, more baths etc).
  • BUFF
    BUFF Posts: 2,185 Forumite
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    k_man said:
    Hi,
    remember that over the winter months the water that you are heating is colder, so that's another consideration.
    Mains water temperature only varies by a few degrees during the year (there was a similar thread last winter),  so this will only make a few % difference.
    Depending upon where you live it can be up to 15C variation in the mains.
  • QrizB
    QrizB Posts: 13,822 Forumite
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    During the months when my radiator heating tends to be zero, my hot water and cooking usage are as follows in kWh: May 635, June 473, July 359, August 381 and September 639.

    I presume that in the colder months, the hot water will take more kWh to heat. Is there a rule of thumb that I can use to estimate my hot water usage during the months when I also use central heating? 
    I don't know a rule of thumb, exactly, but if:
    • You heat your water to 60C;
    • In the summer months the incoming water is at 15C;
    • In the winter months the incoming water is at 5C; and
    • All other factors remain unchanged, then
    Your winter energy use to heat water will be (60-5)/(60-15) ie. 55/45ths or 11/9ths of your summer energy use. That's about 22% more.
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
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  • k_man
    k_man Posts: 1,636 Forumite
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    BUFF said:
    k_man said:
    Hi,
    remember that over the winter months the water that you are heating is colder, so that's another consideration.
    Mains water temperature only varies by a few degrees during the year (there was a similar thread last winter),  so this will only make a few % difference.
    Depending upon where you live it can be up to 15C variation in the mains.
    Thanks, I must have misremembered. Maybe it was daily/weather related variations that were over estimated.
  • Sterlingtimes
    Sterlingtimes Posts: 2,408 Forumite
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    QrizB said:
    During the months when my radiator heating tends to be zero, my hot water and cooking usage are as follows in kWh: May 635, June 473, July 359, August 381 and September 639.

    I presume that in the colder months, the hot water will take more kWh to heat. Is there a rule of thumb that I can use to estimate my hot water usage during the months when I also use central heating? 
    I don't know a rule of thumb, exactly, but if:
    • You heat your water to 60C;
    • In the summer months the incoming water is at 15C;
    • In the winter months the incoming water is at 5C; and
    • All other factors remain unchanged, then
    Your winter energy use to heat water will be (60-5)/(60-15) ie. 55/45ths or 11/9ths of your summer energy use. That's about 22% more.
    Thank you. This is very helpful. 

    But I have realised an error in my calculations. I have forgotten to add in the 444 kWh annual solar diversion, which may explain some of the lower summer readings.

    Nonetheless, I think that your logic is correct and that I need to add more kWh to the winter forecast for hot water heating.
    I have osteoarthritis in my hands so I speak my messages into a microphone using Dragon. Some people make "typos" but I often make "speakos".
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