Thermal store Cylinder Usage

Afternoon,

Recently replaced my pulsa coil 3, a very old thermal store / cylinder which I believe has been in situ for 23 years. It was absolutely knackered and I’ve updated it with a brand new equivalent 180L model - fully insulated.

My question is around how to use it as efficiently as possible. I live in a one bed flat in city centre therefore it’s only used for my hot water. The old unit would use £5 a day!! It would eat up through the night for 5hrs so about a pound an hour, and wouldn’t necessarily cover 3 full showers hot water wise. Hence the change. Can I expect to see a dip in usage and if so why? I’m not clued up and although I’ve been told they’re much more efficient than old ‘boilers’ I’ve nothing really factual to go off. 

I appreciate these systems aren’t the norm but was hoping somebody might be able to help/advise.

Thanks in advance!
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  • Netexporter
    Netexporter Posts: 1,047
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    What tariff are you on? Have you got a smart meter|?
  • mmmmikey
    mmmmikey Posts: 1,594
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    edited 14 November 2023 at 3:42PM

    I have a thermal store a bit like yours which is heated with one or two electric immersion heaters. I live on my own and don't have a dishwasher so use hot water for washing up as well as showering. I typically have a hot shower for about 5 minutes each day with a good flow of water. I use between 3kWh and 4kWh of electricity per day - about £1 worth if you are on a standard tariff. So based on this I would say there is good potential for saving.

    A few questions in addition to the above question about your tariff:

    1. How many people are in your household and how long do they typically shower for?
    2. Do you have a dishwasher
    3. Do you use hot water for anything other than washing and showering?

    edit - forgot to ash what kind of shower you have - is it a "normal" one or a power shower or one of those big high-flow shower heads
  • Is it really a Thermal Store or is it a normal DHW cylinder? 

    With a Thermal Store you pass cold water through the store and it gets heated.  But the water in the store never actually comes in direct contact with the hot water you use.  The only reason I know of for having a water-filled thermal store is so that you can heat it in more than one way, such as with heat from a solar thermal panel and also from a gas boiler.

    What you probably have is a normal DHW cylinder where you use the hot water that is stored inside the cylinder.  
    Reed
  • Thanks for replies.

    dishwasher yes, use it every 2-3 days

    smart meter yes although I’ve got it turned off

    theres 2 of us here, probably average 10minutes or showering a day with just a normal modern shower head nothing fancy or power shower etc

    My tarrif is 31.82p per kWh. 

    Mine has two immersion heaters too, one for the normal every day heating or the thermal store and the other for BOOST

    hope this helps and thanks all for response so far


  • Netexporter
    Netexporter Posts: 1,047
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    As you have a smart meter you could go on a TOU (time of use) tariff and heat the water very much more cheaply.
  • QrizB
    QrizB Posts: 13,682
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    Recently replaced my pulsa coil 3, a very old thermal store / cylinder which I believe has been in situ for 23 years. It was absolutely knackered and I’ve updated it with a brand new equivalent 180L model - fully insulated.
    Thermal stores are a good idea if you have cheap energy at a time of day when you don't want to use it. So, Economy 7 where electricity is cheap overnight. They let you heat water and store it for later in the day, when you want to use it.
    If you don't have a time-of-use tariff, they're a needless waste of money and space.
    My question is around how to use it as efficiently as possible.
    Heat it up wen your electricity is cheap. Use it at other times of day. That's all there is to it.
    The old unit would use £5 a day!! It would eat up through the night for 5hrs so about a pound an hour ...
    Heating 180 litres of water from 20C to 85C takes about 14kWh (link). That would suggest your electricity is about 36p/kWh, which is not E7 cheap rate. What tariff are you on?
    ... and wouldn’t necessarily cover 3 full showers hot water wise. Hence the change.
    Is your new 180 litre thermal store larger than the old one? If not, it probably still won't last.
    Can I expect to see a dip in usage and if so why?
    No, from the info you've provided I don't think you're not going to make any big savings. You might possibly save a 20-30 pence a day if the new thermal store is significantly better insulated than the old one.
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • RedFraggle
    RedFraggle Posts: 1,308
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    I had an external timer fitted to my pulsacoil and it is now only in for 2 of my E7 7 hours 
    Officially in a clique of idiots
  • QrizB
    QrizB Posts: 13,682
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    The only reason I know of for having a water-filled thermal store is so that you can heat it in more than one way, such as with heat from a solar thermal panel and also from a gas boiler.
    A thermal store also lets you have mains-pressure hot water without a combi boiler or a sealed HW tank (so no need for special training or annual inspections).
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • Reed_Richards
    Reed_Richards Posts: 4,006
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    edited 15 November 2023 at 8:44AM
    QrizB said:
    The only reason I know of for having a water-filled thermal store is so that you can heat it in more than one way, such as with heat from a solar thermal panel and also from a gas boiler.
    A thermal store also lets you have mains-pressure hot water without a combi boiler or a sealed HW tank (so no need for special training or annual inspections).
    Yes, I guess that's true.  But my impression is that they are significantly more expensive than regular hot water cylinders and more limited in the rate with which they can output hot water, although for a one bedroom flat flow rate won't be an issue.  I suppose they may well work better in a small property than in a large one; I had not thought of that before. 

    But if the thermal store is not sealed it must need a header tank and not so many flats have a loft where it would go.  
    Reed
  • Bendo
    Bendo Posts: 266
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    A thermal store won't struggle with hot water flow. They will easily run 2 high power showers with no issues.
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