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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 3
    • Magentasue
    • By Magentasue 30th Apr 09, 10:22 AM
    • 4,201 Posts
    • 2,671 Thanks
    Magentasue
    Gas is about a third of the price of electricity. Check on comparison websites - you may be better off on a single rate tariff. There's no fixed percentage that makes it a good idea and, whereas the rule of thumb used to be that you could break even using 25% of electricity off-peak, this is no longer the case. May work for you but worth checking rather than assuming it's still worthwhile.
  • ben37564
    Woah....do not.. under any circumstances leave the immersion on all the time. They use a lot of electricity and are hugely expensive to run.
  • Dinx
    even using the 2 rate meter? using it during the night?
    • Magentasue
    • By Magentasue 30th Apr 09, 1:22 PM
    • 4,201 Posts
    • 2,671 Thanks
    Magentasue
    How much are you paying per kwh for gas? How much for off peak electricity.
  • Dinx
    ok let me do some research.

    I am on the standard dual fuel trarrif

    gas -
    tier 1 7.160p per kwh
    tier 2 3.410p per kwh

    electricity
    night flat rate 5.584p kwh
    day tier 1 32.379p kwh
    day tier 2 12.157 kwh

    vat inclu
    • Magentasue
    • By Magentasue 30th Apr 09, 1:48 PM
    • 4,201 Posts
    • 2,671 Thanks
    Magentasue
    Assuming you use enough gas to pay for all of the tier 1 kwh, you would be paying 3.4p per kwh to heat your water by gas, or 5.6p by electricity.
  • Dinx
    ok I understand that. I just really have to work out how much units are charged at tier 1.

    only use the immersion heater while I am in tier one and then let the gas boiler do rest of the work when I hit tier two.
  • Dinx
    Tier 1 applies to the first 670 kWh per quarter (2680 kWh per annum for Pay As You Go Energy™) and all subsequent consumption is charged at Tier 2.

    thats is copied from British Gas website.

    this gets very confusing now becuase bills dated dec says i have been charged first 749kwh at tier one and then my latest bills is 661kwh at tier one. either there has been a change in the amounts of units in tier one or I have been billed wrongly.
    • Magentasue
    • By Magentasue 30th Apr 09, 2:12 PM
    • 4,201 Posts
    • 2,671 Thanks
    Magentasue
    thats is copied from British Gas website.

    this gets very confusing now becuase bills dated dec says i have been charged first 749kwh at tier one and then my latest bills is 661kwh at tier one. either there has been a change in the amounts of units in tier one or I have been billed wrongly.
    Originally posted by Dinx
    Different number of days in those quarters?
  • Dinx
    could be then becuase I have always sent a meter reading just to make sure its all correct and I sent a new bill with the updates changing the number of days in a quarter. I need to dig up the past few bills now the online account only lets me go back 3 bills.
    • Cardew
    • By Cardew 1st May 09, 1:57 PM
    • 28,028 Posts
    • 13,876 Thanks
    Cardew
    Woah....do not.. under any circumstances leave the immersion on all the time. They use a lot of electricity and are hugely expensive to run.
    Originally posted by ben37564
    Within reason it doesn't matter how long you leave them on as they all have a thermostat which switches them off - just like your electric kettle. except the thermostat switches them off at a set temperature, say, 65C.

    There really is a lot of nonsense talked about the huge cost of leaving on immersion heaters 24/7.

    Whilst I am not in any way suggesting you should leave it on 24/7 the real difference between 24/7 and timed is not more than 1kWh to 2kWh a day.
  • skelly01
    Have too disagree with you Cardew regarding leaving your immersion heater on.
    I live in a brand new house, with a very modern saniflo hot water tank, which is lagged to the hilt.
    I used to leave the immersion heater on all day long, but have since changed to timed. I am saving around 8kwh (units) per day.
    So there is proof that the savings are in not leaving it on 24/7.
  • djohn2002uk
    Have too disagree with you Cardew regarding leaving your immersion heater on.
    I live in a brand new house, with a very modern saniflo hot water tank, which is lagged to the hilt.
    I used to leave the immersion heater on all day long, but have since changed to timed. I am saving around 8kwh (units) per day.
    So there is proof that the savings are in not leaving it on 24/7.
    Originally posted by skelly01
    Then I sugest that there is either something wrong with the thermostat or you are using less hot water since you switched to "timed".
    If, as you say, the tank is "lagged to the hilt" then where was/is all the heat going? Youre figures just defy logic and physics.
    • Cardew
    • By Cardew 18th May 09, 4:58 PM
    • 28,028 Posts
    • 13,876 Thanks
    Cardew
    Have too disagree with you Cardew regarding leaving your immersion heater on.
    I live in a brand new house, with a very modern saniflo hot water tank, which is lagged to the hilt.
    I used to leave the immersion heater on all day long, but have since changed to timed. I am saving around 8kwh (units) per day.
    So there is proof that the savings are in not leaving it on 24/7.
    Originally posted by skelly01
    It is not 'proof' I am afraid! and you are not disagreeing with me but the people at British Standards who test hot water cylinders.

    Unfortunately it will cost you 42 to buy the British Standard:

    http://www.bsi-global.com/en/Shop/Publication-Detail/?pid=000000000000150928

    However you can look on the internet and find lots of statements like this:

    All hot water cylinders lose energy even if no hot water is being used. The technical term is called "standing loss". Standing losses will always occur and a well insulated electric hot water cylinder may have heat losses of about 2kwh/day
    Or this:

    Thermal Insulation:
    CFC/HCFC free (ODP Zero) fire-retardant expanded polyurethane (40-50mm thick). GWP 3.1 (Global Warming Potential)
    Standing Heat Loss Figures (kWh/24h)
    70ltr 1.10
    125ltr 1.49
    145ltr 1.65
    170ltr 1.77
    210ltr 1.97
    250ltr 2.09
    300ltr 2.25


    Does your Saniflo tank have a heat loss figure on a label?

    Have you looked at the tested heat loss from your Saniflo tank? Or contacted them to ask what is the loss per day?
  • david17589
    yes thats ok turn it down from thermostat and you will save loads and if you have a boiler turn it down from there aswell...
  • skelly01
    I am only stating what I have found. I use the same amount of water, have not touched the thermostat and by switching from always on to timed only (3 x 2 hour slots throughout 24 hours)
    So how that is not proof I do not know, its bare faced facts in my case.
    I wasnt arguing with Cardew over the heat loss element. As for the lables etc no I have not looked. I was stating what I have saved by switching from always on to timed only.
    There is nothing wrong with the element, thermostat or any of the workings. I have hot water at the temperature I need and want and as I stated I use the same amount roughly.
    The thread is about either keeping on all the time or switching to timed. My personal experience is I save by switching to timed.
    I might read the standard, although find them all very boring, it wouldn't cost me as my employer subscribes to the BSi site.
    No debate in my personal experience.
  • NowThenAgain
    I think the disagreement here is due to the difference between:

    1. Maintaining a tank full of water at a required temperature for 24 hours. NO WATER USAGE. The Cardew / boiler label situation.

    2. Using some of the heated water so causing cold water to be brought into tank and be heated to the required temperature. The skelly01 situation.

    Of course, situation 2 is the reality and therefore the savings from having the tank mostly off may well reach to 8 KWH/day.
    • Cardew
    • By Cardew 20th May 09, 2:09 PM
    • 28,028 Posts
    • 13,876 Thanks
    Cardew
    I think the disagreement here is due to the difference between:

    1. Maintaining a tank full of water at a required temperature for 24 hours. NO WATER USAGE. The Cardew / boiler label situation.

    2. Using some of the heated water so causing cold water to be brought into tank and be heated to the required temperature. The skelly01 situation.

    Of course, situation 2 is the reality and therefore the savings from having the tank mostly off may well reach to 8 KWH/day.
    Originally posted by NowThenAgain
    I am sorry but you are totally missing the point.

    1. If I have a tank full of hot water, and use none of that water, it will consume, say, 2kWh to maintain that water at the required temperature for 24 hours. That is the loss from the tank.

    2. That is a worse case scenario.

    3. If you use xxx litres of hot water, it will have used yy kWh to heat that water - that is nothing to do with heat losses.

    So for a given amount of hot water(at the same temperature) used, the difference between having your immersion on 24/7 or timed cannot be more than 2kWh. How can you save 8kWh a day when the maximum losses are only 2 kWh?

    Indeed the average annual consumption of energy to provide domestic hot water is under 3,000kWh, so to 'save' 8kWh a day( 2,920kWh pa) by having water timed is simply not supportable.
  • NowThenAgain
    Hum.

    So if I were to heat up a tank of hot water, then drain that tank completely, then heat the tank fully again, then drain it, then heat it, are you saying this usage would not exceed 2KWh?

    I say it would and that is my point. In normal use (with, lets say, 1 bath per day, a couple of showers, other water usage) you are continually drawing cold water into the system. This requires a lot of energy to heat.

    Personally, I have my immersion almost permanently off.
  • paceinternet
    The explanation is that you will not loose more than 2kwh per day through heat loss from the tank however many times you fill it.
    This is not the same as how many kwh you might use in different timed scanarios to heat the water. You are most likely wasting higher temperature water when it is permanently on, and accepting lower temperature water when it is timed.

    The saving on timed heating can only be because part of the tank is at lower temperature for parts of the day, so the heat loss is less due to temperature differences. Simple example being if half the tank was cold water, and half hot, you would loose 50% of the 2kw heat loss compared to if it was all hot. Yes?

    So, I don't doubt you can achieve savings by using timed water, but it is due to the way you use the water, and you are not comparing the same useage. If you are comfy with what comes out of the taps on timed water, then it is the best solution for you.
    Last edited by paceinternet; 20-05-2009 at 5:20 PM.
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