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  • FIRST POST
    filigree
    Cheapest way to use the immersion heater
    • #1
    • 12th May 05, 11:04 AM
    Cheapest way to use the immersion heater 12th May 05 at 11:04 AM
    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:
Page 5
    • Chef1980uk
    • By Chef1980uk 15th Jun 09, 8:37 PM
    • 218 Posts
    • 39 Thanks
    Chef1980uk
    Interesting thread. Having moved in to our new house 2 weeks ago i am keen to find out the answer to this very question. Our set up is no gas supply, coal fire with rear water heater for radiators and hot water supply, an electric water heater/immersion upstairs, and a pull cord for hot water to shower.

    We need hot water for showers X 2 adults and baths X 3 babies. A dishwasher takes care of the washing up but baby bottles need hot water in the sink.

    We think we need hot water supply for any 6 hours between 8am and 8pm. What we can't figure out is the cheapest way to get supply that.

    a: Leave immersion on during the day
    b: leave immersion on during the night
    c: Don't use the immersion but coal fire going constantly on low (5 per day in coal)
    D: another way?
  • paceinternet
    Your immersion is likely to be 3kw.
    Your electricity cost roughly 10p per kwh.
    So 30p an hour.
    Even if it is on continuously for 6 hours, it will cost no more than 1.80 per day.
    Probably the best solution in summer when you are not needing radiator heat.
    In winter, ??? I guess you have to let it heat the water as you probably can't stop it doing so.

    However, if your shower is a pull cord, it may be an electric shower, which will cost you an additional amount of electricity regardless of the immersion being on.
  • trisha909
    my house is bloody freezing all the time and thats with my central heating on full blast!. I have an immersion heater too and have had to use that occasionally. As an eyeopener, on moving into this house in three months (3 weeks of that not yet residing here fully) I was told to have my heating on at about 18 c all the time. I did over the winter months apart from that three weeks i mentioned and when my bill arrived it was 598 gas alone!. Im scared to put it on now it goes on 1 hr in the morning and evening and my hot water once a day for 1 hr
    Trisha

    When I die, I want to go peacefully like my Grandfather did, in his sleep -- not screaming, like the passengers in his car.
    • Wickedkitten
    • By Wickedkitten 16th Dec 09, 9:39 PM
    • 1,820 Posts
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    Wickedkitten
    Whoever told you to keep it on all the time needs a clip round the ear.
    It's not easy having a good time. Even smiling makes my face ache.
    • JennyR68
    • By JennyR68 14th Jan 10, 2:18 PM
    • 416 Posts
    • 247 Thanks
    JennyR68
    Your immersion is likely to be 3kw.

    However, if your shower is a pull cord, it may be an electric shower, which will cost you an additional amount of electricity regardless of the immersion being on.
    Originally posted by paceinternet
    I've seen days when my family have used 1.50 to use the electric shower alone (teenage girls, why is it even when I've timed them and watched the monitor clock up they are still convinced they were only in '5mins'? ). It's days are numbered, waiting for plumber to put new unvented direct tank in now to run a mixer shower instead.

    Has anyone any advice on whether to get a 210l or 250l to suit a family of 5 showers and hand dishwashing?

    Or am I right in thinking that what Cardew is saying is that either size would do if I kept it switched on, wouldn't make much difference as would use roughly same energy to heat 250l in one go as 250l in stages in a 210l tank?
    Last edited by JennyR68; 14-01-2010 at 2:33 PM.
    • Cardew
    • By Cardew 14th Jan 10, 6:59 PM
    • 28,084 Posts
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    Cardew
    I've seen days when my family have used 1.50 to use the electric shower alone (teenage girls, why is it even when I've timed them and watched the monitor clock up they are still convinced they were only in '5mins'? ). It's days are numbered, waiting for plumber to put new unvented direct tank in now to run a mixer shower instead.

    Has anyone any advice on whether to get a 210l or 250l to suit a family of 5 showers and hand dishwashing?

    Or am I right in thinking that what Cardew is saying is that either size would do if I kept it switched on, wouldn't make much difference as would use roughly same energy to heat 250l in one go as 250l in stages in a 210l tank?
    Originally posted by JennyR68
    What am I saying?

    JennyR68,

    Are you serious with the nonsense you keep posting, or just amusung yourself(and us!!)?

    As I understand it you have an all electric property and are not on an E7 tariff.

    You have an Electric shower, but as it uses too much electricity, you intend to get an unvented direct tank(which presumably you will heat with an immersion heater) and run a mixer shower from the tank?

    Isn't that rather like saying that my electric kettle uses too much electricity heating water for a cup of tea, so I will heat up a 20 litre saucepan of water on my electric cooker?

    Run this by me again please!
    • JennyR68
    • By JennyR68 14th Jan 10, 10:04 PM
    • 416 Posts
    • 247 Thanks
    JennyR68
    Too much to hope for a simple answer to a simple question? :confused:

    Electric shower on last legs, useless as well as expensive. However as completely redoing bathroom part of the makeover is replacing ancient water tank and we don't have to replace shower with another electric. Plumber advised putting in direct unvented as that is what one does these days. Gives pressurised hot water and will result in much better shower from a thermostatic mixer.

    Why is there a problem with that?
    • dave_dph
    • By dave_dph 15th Jan 10, 9:32 PM
    • 538 Posts
    • 170 Thanks
    dave_dph
    Too much to hope for a simple answer to a simple question? :confused:

    Electric shower on last legs, useless as well as expensive. However as completely redoing bathroom part of the makeover is replacing ancient water tank and we don't have to replace shower with another electric. Plumber advised putting in direct unvented as that is what one does these days. Gives pressurised hot water and will result in much better shower from a thermostatic mixer.

    Why is there a problem with that?
    Originally posted by JennyR68
    I have a pressurised unvented direct cylinder which heats up on ec7, so I always have stored hot water. When the tank was installed last year I also had a Mira Miniduo mixer shower installed, which runs on the pressurised hot water. Trust me, the shower performance is excellent, best one I have ever used! Even the guys who installed the bathroom & shower could not believe how powerful it is. You will not be diappointed.
    • Cardew
    • By Cardew 15th Jan 10, 10:04 PM
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    • 13,925 Thanks
    Cardew
    I have a pressurised unvented direct cylinder which heats up on ec7, so I always have stored hot water. When the tank was installed last year I also had a Mira Miniduo mixer shower installed, which runs on the pressurised hot water. Trust me, the shower performance is excellent, best one I have ever used! Even the guys who installed the bathroom & shower could not believe how powerful it is. You will not be diappointed.
    Originally posted by dave_dph
    That is exactly the point being made!

    A good mixer shower will have great performance and make most electric showers seem like a dribble.

    However such performance uses a lot more hot water, and when the hot water tank is heated by an immersion heater on 'normal'(i.e. not E7) rates it will obviously be a lot more expensive than the electric shower about which JennyR68 was complaining.
    • JennyR68
    • By JennyR68 15th Jan 10, 10:09 PM
    • 416 Posts
    • 247 Thanks
    JennyR68
    That is exactly the point being made!

    A good mixer shower will have great performance and make most electric showers seem like a dribble.

    However such performance uses a lot more hot water, and when the hot water tank is heated by an immersion heater on 'normal'(i.e. not E7) rates it will obviously be a lot more expensive than the electric shower about which JennyR68 was complaining.
    Originally posted by Cardew
    JennyR68 is complaining about paying a fortune for an absolutely useless shower, wouldn't care what she paid for a decent one!
    • Cardew
    • By Cardew 15th Jan 10, 11:12 PM
    • 28,084 Posts
    • 13,925 Thanks
    Cardew
    JennyR68 is complaining about paying a fortune for an absolutely useless shower, wouldn't care what she paid for a decent one!
    Originally posted by JennyR68
    So if it uses 1.50 for showering and is 'absolutely useless' how is the electricity being used?

    Energy cannot be destroyed(according to the law of thermodynamics) so the heat must go somewhere.
    • Kirri
    • By Kirri 15th Jan 10, 11:21 PM
    • 6,139 Posts
    • 21,108 Thanks
    Kirri
    When I first moved in the previous owner left no instructions on how to set the timer on the immersion so it was on constantly. Had HUGE bill.

    Found how to do it after that and set it for hour am and hour pm and my bill really dropped. No way would I leave it on full time again!
    • JennyR68
    • By JennyR68 16th Jan 10, 9:39 AM
    • 416 Posts
    • 247 Thanks
    JennyR68
    So if it uses 1.50 for showering and is 'absolutely useless' how is the electricity being used?

    Energy cannot be destroyed(according to the law of thermodynamics) so the heat must go somewhere.
    Originally posted by Cardew
    I'm not sure what your trying to do here Cardew. But I didn't come on this thread to discuss my shower.

    The question was what size of tank does one think best for family of 5. If you have an unvented direct tank and a family of 5 and think you can help with the question please do so.

    If not, get your neck in! I'm not 'playing' today.
    • tori.k
    • By tori.k 16th Jan 10, 11:48 AM
    • 3,532 Posts
    • 9,478 Thanks
    tori.k
    I've just had my leccy bill, i have immersion water heater and my bill states im using 5 less units a day by switching off...but i have a duel immersion so dont heat the whole tank
    • Cardew
    • By Cardew 16th Jan 10, 5:07 PM
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    • 13,925 Thanks
    Cardew
    I'm not sure what your trying to do here Cardew. But I didn't come on this thread to discuss my shower.
    Originally posted by JennyR68
    Sorry I thought the quotes below indicated you were discussing showers!!

    QUOTE=JennyR68
    1. I've seen days when my family have used 1.50 to use the electric shower alone (teenage girls, why is it even when I've timed them and watched the monitor clock up they are still convinced they were only in '5mins'? ). It's days are numbered, waiting for plumber to put new unvented direct tank in now to run a mixer shower instead.

    2. Electric shower on last legs, useless as well as expensive. However as completely redoing bathroom part of the makeover is replacing ancient water tank and we don't have to replace shower with another electric. Plumber advised putting in direct unvented as that is what one does these days. Gives pressurised hot water and will result in much better shower from a thermostatic mixer.

    3. JennyR68 is complaining about paying a fortune for an absolutely useless shower, wouldn't care what she paid for a decent one!
    • JennyR68
    • By JennyR68 16th Jan 10, 5:56 PM
    • 416 Posts
    • 247 Thanks
    JennyR68
    No my dear that was you trying to discuss showers with me, I merely agreed with what someone else was saying and gave evidence to support and suggest just how much extra we could be talking about. I did not intend to have a conversation with you about it, it was you that initiated that.

    I went to go on to post the real reason I was looking at the thread. Why you decide to pose questions on something that was not a question and not answer the real question, which you appear perfectly qualified to do with your wealth of expertise at calculating water heat things, is probably very confusing to some people and making you look just a wee bit daft.
    • Mr Proctalgia
    • By Mr Proctalgia 17th Jan 10, 12:14 AM
    • 961 Posts
    • 818 Thanks
    Mr Proctalgia
    I think the question is perhaps impossible to answer, so much depends on usage patterns and what is available to the user.
    If you heat something up it will take energy, if you leave it stood it will cool down - eventually. No if's and no buts, it is fact.

    I therefore think it is up to the user of the heated water to look at their needs and usage patterns before deciding what is right for themselves. If you use a little water occasionally then boil a kettle or use an equivalent means. Perhaps an undersink heater or instantaneous water hear will suffice. If you want a shower a day then an electric one is perhaps the way forward. Should you be fortunate to have a family then stored hot water will work for you providing you use it all and do not leave some to be diluted with cold water that will replace it.
    I realise that this will lead to several arguments, firstly that the incoming cold water will be heated by the remnants of the hot water and so use less energy to heat up - But only if you heat it up straight away, and if you do not use it straight away then it will start to cool anyway. You will also use more energy heating water from a lower temperature if your tank is cold - So I really do not know the answer to this one.

    A further factor to consider is heat loss, if your airing cupboard is warm then you are losing heat, if your pipes are hot then you are losing heat, this may be beneficial heat loss as it is helping to heat your home but it is all helping to cool your water down, so if you want to control your heat loss then insulate your pipes and tanks - Remember even a Thermos Flask cools down!

    There is no totally efficient fuel, electricity is just about 100% efficient at the point of use but is expensive, gas is at best about 90% efficient at point of use but suffers significant losses in pipes and the waste of water as a combi boiler gets "up to speed" An unvented cylinder is nice as it will give you as good a flow as the mains will provide, the choice of heating up the water inside is up to the user, the use of the old copper cylinder I feel in this day and age is an anachronism, it is after all is said and done little more than a bulge in a pipe with hot water in it and has little pressure and many potential problems.

    So what do I do? My kitchen sink is miles away from my tank so I have a 10 litre undersink 2Kw mains pressure heater, I use it as needed and it is set to a high (80 Deg C ) temp, it works for me as I tend to wash up infrequently and use a full load of hot water. It is plumbed in 10mm Hep2O so wastes about 200 ml of cold water before the hot comes through.
    I shower daily so have a 9Kw instantaneous heater, it has been sufficient down to the recent -8 Deg C I have experienced. I also use this same heater to fill my hand basin for a shave and tooth brushing session, I can have a bowl full of hot water after 45 seconds or so at 9Kw ph and have no need to heat my cylinder at all.
    If you want the convenience of hot water on demand then you are going to have to pay for the privilege, the second you make water hotter than the room it is in it starts to cool, yes, even as you heat it it loses heat, before it gets to your taps it heats the pipes and cools down, and then we let hot water go down the drain! This thread should make all of us think!
    I will add that I do not have gas, my electricity bill is around 100 per quarter, my water cost me 6 per month (metered) but is in credit now, my coal bill is the subject of another thread!
    The quicker you fall behind, the longer you have to catch up...
  • argonout
    Well done to the last thread at concluding the debate so well and using the obvious when taking time to think outside the box a bit. I hope the 2kw/8kw argument has been explained a little...........

    Not just heat loss from the tank but also the pipes around the tank, to the taps and also I might hypothesize myself that maybe insulation may become less effective over time?, maybe the immersion may have been there 1 year or 30 years???

    But I think the key is to leave it on to heat the tank enough for the amount of water needed to be used. For instance if we say a tank reaches tempreture in an hour then if you use a tank a day have it on an hour before you get up. If you use half a tank then have it on for 30mins. More than a tank then then maybe have it on for 30/60mins in the afternoon.

    I think with some experimenting you could get a happy medium with the risk of having cold water a few times.

    In a nutshell your looking at 2kw to 8kw a day heat loss with a well insulated to not well insulated system taking into account pipes/filling tanks having it on timed. Remember take off 4% off that if you have it on for an hour, 8% 2 hours etc.... 1hr on , 23hrs not being on constantly.........

    Hope this is clear??????????

    Cardew, open your mind a little my friend

    Jen, this was about cheapest way to use an immersion

    Chill out guys, this site is for enlightenment!!
    • Cardew
    • By Cardew 14th Feb 10, 8:00 PM
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    • 13,925 Thanks
    Cardew
    In a nutshell your looking at 2kw to 8kw a day heat loss with a well insulated to not well insulated system taking into account pipes/filling tanks having it on timed. Remember take off 4% off that if you have it on for an hour, 8% 2 hours etc.... 1hr on , 23hrs not being on constantly.........
    Originally posted by argonout

    Hope this is clear??????????

    Cardew, open your mind a little my friend

    Jen, this was about cheapest way to use an immersion

    Chill out guys, this site is for enlightenment!!
    Originally posted by argonout
    Welcome to the forum!

    I am afraid I am not clear of the point you are trying to make, or at least why I need to open my mind?

    You will find if you peruse this site, that many people think having the hot water on all the time will cost a huge amount more than having it timed. Some apparently are unaware of a thermostat or its purpose.

    My point in this, and other, threads is that whilst a timer is obviously cheaper the difference is not massive.

    So as an example take a HW tank that loses 2.3kWh in 24 hours when filled with water at 65C (as tested to a British Standard) - see below.

    Even if you leave the tank on 24/7 you are not going to lose more than 2.3kWh a day.(and of course the lost heat warms the house - which is why it is often in an airing cupboard)

    Having it timed will reduce this 2.3kWh loss.

    Now perhaps you can explain why you feel I should open my mind?



    Last edited by Cardew; 14-02-2010 at 9:39 PM. Reason: sp
  • albyota
    Another point to make is, if an electric immersion heater is used, then its position in the cylinder will make a difference.....an element in the bottom means a greater amount of water can be heated 180 - 200/250L, and with stratification (hot water rises to top) the hotter water will sit at the top. With a single element positioned in the top, the element will mostly only heat the top section of water, depending on setting of thermostat, so probably 80 - 100 litres, whereas the bottom of the cylinder will be cool. the more water you heat the more it will cost, if you only use a small amount of water in a cylinder, make sure the element is fitted in the top.....a lot of the larger cylinders (like cardews above) will have an element top and bottom, the top for E7 peak day rate boost....the bottom one for cheap off peak.
    Last edited by albyota; 14-02-2010 at 8:58 PM.
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