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Cheapest way to use the immersion heater

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Cheapest way to use the immersion heater

edited 30 November -1 at 12:00AM in Energy
150 replies 319.1K views
filigree_2filigree_2 Forumite
1K posts
edited 30 November -1 at 12:00AM in Energy
We have a temporary problem with the gas powered hot water and heating. In the short term we are using the electric immersion for hot water.

Does anyone know if it is more economical to

leave it on all the time
switch it on as needed
switch it on for a fixed period each day?

There are three of us with the usual needs for baths and a washing machine.

Years ago a plumber told me it was cheapest to leave it on all the time so the thermostat only kicked in occasionally to keep it hot. He said it used MORE fuel to heat up water from cold every time. I don't know about these things so does anyone have any ideas? Thanks :confused:
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Replies

  • He was right.......leave it on.

    save a little by turning the thermostat control down a touch........no-one will notice;)
  • Paul_VarjakPaul_Varjak Forumite
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    Just understand and remember the following: "The rate of loss of heat is proportional to the temperature differential" and you have your answer!
    Any opinions are my own unless otherwise stated.
  • chriswchrisw Forumite
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    He said it used MORE fuel to heat up water from cold every time.

    Rubbish! Assuming no heat loss, a given amount of water requires a given amount of energy to raise the temperature a given amount.

    However, as the above poster infers, the rate of heat loss is greater for a hot tank than a cooler one so the thermostat is only responding to wasted heat loss.

    Leaving the heater on is therefore the most expensive option - it should only be switched on when needed, or at least switched off overnight to minimise heat loss.
  • djohn2002ukdjohn2002uk Forumite
    2.3K posts
    All the above posts are partially right but are using too much technical theory to explain a practical situation.

    Leaving the immertion heater on can waste heat in 2 ways.
    Firstly there is no way there can be no heat loss. No one has invented the "perfect" insulation for a cylinder, and, there is heat loss by conduction to the adjacent pipework.
    Secondly, as long as there is known to be constant hot water it will be used resulting in a considerable quantity of hot water left in the pipework to the tap, which is not normally lagged and so loses its heat rapidly.

    Heating a 40 gallon cylinder from cold is therefore a better option if you are going to use the 40 gallons, otherwise you will be replacing what you take out with cold water reducing the temperature in the cylinder in time to a level that then needs reheating.

    If you are going to rely on an immertion heater for long periods then a dual heater is more economical where a short element heats just the top part of the cylinder and you can leave this on, and switch the second longer element on only when more hot water is needed for baths etc.
    Heating just the top of the cylinder means aprox. 10 gallons which, because hot water always rises to the top of the cylinder, it stays at the top and the cold at the bottom.

    Otherwise the cheapest option is probably to have your gas heating system switched to Hot Water Only.
  • BadgergalBadgergal Forumite
    531 posts
    Can I hijack this thread please to ask a question about my immersion...

    I live in a tiny studio flat with only a gas fire and no central heating etc, and the water is heated by an immersion. I turn this immersion on for 2-3 hours every day and that is enough for a shower and washing up. Even though the tank wears a thick jacket the water never stays hot for more than a few hours so I have to time it carefully, but I'm used to it.

    I read through some posts about it being cheaper to leave on all the time and they confused me - is there a cheaper way than my way of putting it on for 3 hours max every day (some days I don't even put it on, e.g if I stay over at someones)?
  • Important update! We have recently reviewed and updated our Forum Rules and FAQs. Please take the time to familiarise yourself with the latest version.
  • scattycat_3scattycat_3 Forumite
    509 posts
    Badgergal, you are not hijacking the thread, but hitting the nail on the head.

    Unless people are prepared to make (Expensive ) alterations to their systems, your method is the cheapest,[imho ;) ]. We dont leave the kettle boiling constantly in case we need a cuppa, do we.
    You could make it cheaper by adding a thicker insulating jacket. The thicker the better. If you can pack the space around it with insulation then do so, any trapped air products like polystyrene, bubblewrap etc.
    Packing is a good cheap source of these products. You could also use small plastic freezer bags filled with air and then sealed, like balloons. Put the most insulation at the top, as heat rises, and you will be surprised how much longer your water will stay hot.

    Gas is the cheapest, even though less efficient, it cost so much less per KWh.
    The dj's twin element heater is the next best option, BUT good insulation is the most important thing.
    As has been stated the heat loss is proportional to the temperature difference around an object, that is why we wear more clothes in Winter,:D

    TRAF SEE ME!!! :p
    Moi....? ;)

    Martin asked me to say I'm a volunteer Board Guide on the Utilities board, facilitating its smooth running. I can move & change posts there. However I do not read every post.
    Dealing with abusive or illegal posts is not part of my role, so if you spot any, please report them HERE.
    Views I express are mine alone, and not official ones of MoneySavingExpert.com
  • BadgergalBadgergal Forumite
    531 posts
    Thanks very much scattycat, I will consider piling some more stuff on top of the thing. Its really ancient as my trainee electrician boyf discovered when he fitted a timer to it - the wiring was very old.

    Any ideas how much it would cost to get the twin element thing put in? I'm sure it doesn't have one of those already, as it just doesn't do heating small amounts of water e.g. if I only need to wash up.
  • scattycat_3scattycat_3 Forumite
    509 posts
    Regarding washing up, why dont you just boil a kettle (or two if necessary ). A litre of boiled water will give you nearly two litres of hottish washing up water.

    Regarding the immersion heater you could ask your landlord to fit one, at a guess I would say it would cost £50 to £100, really depends were you live. I will try to find the price of one, they didnt use to be expensive. Perhaps your boyfriend could get one wholesale or cheaper. Fitting just require the water to the cylinder to be turned off and it drained down as far as the heater fixing. Then just a big (special, better to borrow one, but B&Q etc sell them) spanner and hope that the old heater hasnt coroded to much, so it comes out without too much effort. Fitting is the reverse , you just have to make sure it is properly sealed against leaks.
    Moi....? ;)

    Martin asked me to say I'm a volunteer Board Guide on the Utilities board, facilitating its smooth running. I can move & change posts there. However I do not read every post.
    Dealing with abusive or illegal posts is not part of my role, so if you spot any, please report them HERE.
    Views I express are mine alone, and not official ones of MoneySavingExpert.com
  • Paul_VarjakPaul_Varjak Forumite
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    Part of the Furniture 1,000 Posts Photogenic Combo Breaker
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    I would endorse most of what has been said.

    1. Avoid using immersion heaters if you have gas central heating - use the gas boiler instead. However, if you have two immersion elements fitted and only need a little hot water then using the upper element to heat a litte water may be cheaper than heating whole tank with gas boiler (also quicker, so you may only have to switch on immersion when you need it).

    2. Remember that immersion heaters have a separate thermostat to the central heating system. Very often, the thermostat on the immersion is way to high. That not only wastes money but is a potential scald risk - especially for babies/young children and the elderly. Thermostat should be no more than 60 centigrade (preferabaly even lower).

    3. If you buy a new tank jacket, don't remove he old one - just fit the new one over the top.
    Any opinions are my own unless otherwise stated.
  • bestymanbestyman Forumite
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    Scattycat wrote:
    Regarding washing up, why dont you just boil a kettle (or two if necessary ). A litre of boiled water will give you nearly two litres of hottish washing up water.

    Regarding the immersion heater you could ask your landlord to fit one, at a guess I would say it would cost £50 to £100, really depends were you live. I will try to find the price of one, they didnt use to be expensive. Perhaps your boyfriend could get one wholesale or cheaper. Fitting just require the water to the cylinder to be turned off and it drained down as far as the heater fixing. Then just a big (special, better to borrow one, but B&Q etc sell them) spanner and hope that the old heater hasnt coroded to much, so it comes out without too much effort. Fitting is the reverse , you just have to make sure it is properly sealed against leaks.

    99% of cylinders only have one boss( hole) so there will be nowhere to screw it in to.
    It is possible to fit a new boss , but you will have to find a very good and probably old plumber who is good at wiping joints. Not many around nowadays. Not a job for the DIYer.
    On the internet you can be anything you want.It`s strange so many people choose to be rude and stupid.
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