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Cheapest way to use the immersion heater

edited 30 November -1 at 1:00AM in Energy
150 replies 308.8K views
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Replies

  • CardewCardew Forumite
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    It is not clear what system you have.

    You would normally only use an immersion heater if the gas CH has broken down as it is much more expensive than gas.

    A combi boiler is one that normally heats the water "as it is used"; however they usually don't have a hot water tank. However some systems(normally conversions of CH systems) do retain a hot water tank as it has the advantages of providing a plentiful supply of hot water - for instance no Combi boiler could provide sufficient HW for a power shower.

    So if you have a gas combi boiler(not convection heater!) that feeds hot water to an immersion tank, and you are running out of hot water, it is probably because the combi water heating is not on for a long enough time. The system might be set so that CH takes priority over water heating.

    Of course it might well be that the HW tank is not even connected to the HW system. If they converted from a conventional CH boiler system to a Combi boiler system, it may have been too difficult to remove the HW tank and piping.
  • italiaitalia Forumite
    214 posts
    ok i've read a the above and am still not sure what to do! i have a immersion tank, dual element, i was given no instructions with it from the developer but there is the top element and lower on, i understand the top one heats small amount at the top and the bottom one the whole tank. i've had the whole tank bottom one left on ALL the time. i dont know if this is the cheapest thing to go. i can look to turning the thermstate down a little as i think its too hot.

    i mainly use hot water in the morning for a shower so i dont need it hot all day and all night. however is switching it off during the day a false economy?

    i am with scottish power and they tell me my overnight electric is a quarter of the price of during the day.

    should i;

    1) leave bottom emmersion on all the time

    2) switch the bottom one one before i go to bed on cheap electric and off in the morning after my shower.

    3) leave it off all together and switch the top (boost) emersion on 20 mins before my shower?

    any help greatly appreciated, but does anyone know which is the right thing to do there are very different opinions on this thread.

    i live in a small new flat and its just me and i am out 5 days a week yet my electric (no gas) is costing 75 a month during the winter and i can't afford it.
    i think its mainly the electric heating but i think i am wasting money heating the tank all the time ????
  • CardewCardew Forumite
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    If your flat is new(you say 'small new flat') then it will have a well insulated HW tank. This means it will lose little heat.

    As you are on Economy 7("your electricity being a quarter of the price of during the day') you want to ensure that you have the immersion heater on only during the 7 hours cheap electricity at night. To achieve this you might need to fit a timer.

    Frankly I would just have the timer set so the whole tank is switched on for a couple of hours in the early hours of the morning.

    You need to determine when that 7 hours is for your flat.

    The other point is that £75 a month, in winter, for an all electric flat is very cheap. As you suspect, most of that is down to heating rather than hot water.
  • Cardew wrote: »
    As you are on Economy 7("your electricity being a quarter of the price of during the day') you want to ensure that you have the immersion heater on only during the 7 hours cheap electricity at night. To achieve this you might need to fit a timer.

    Frankly I would just have the timer set so the whole tank is switched on for a couple of hours in the early hours of the morning.

    You need to determine when that 7 hours is for your flat.
    .


    I second this, the idea is the bottom heater (which heats the whole tank) comes on during the cheap-rate over night and heats the whole tank that (in theory) being well insulated will retain enough heat to have hotwater for the rest of the day.

    The top heater is used for boosting JUST the top part of the tank (heat rises remember) if the water previously heated over night at cheap-rate runs out - i.e. you are using more expensive leccy (peak rate) BUT you are only heating a small volume of water compared to the whole tank.

    Like Cadrew says, you may need a timer fitting so that the bottom heater only comes on during off-peak (also periodically check that the time hasn't drifted too far!) however, you may find that the bottom heater has been wired to a seperate circuit that is only live during off-peak (like I have) so you don't need to worry about timers.

    HTH
    :confused: I have a poll / discussion on Economy 7 / 10 off-peak usage (as a % or total) and ways to improve it but I'm not allowed to link to it so have a look on the gas/elec forum if you would like to vote or discuss.:cool:
  • italia wrote: »
    3) leave it off all together and switch the top (boost) emersion on 20 mins before my shower?

    That option is only likely to be viable if you ONLY EVER use hot water for a shower and NOTHING else at all. BUT, if this is the case, you need to work out how long it would be on for in total (20 mins before shower may not be enough from totally cold - it is designed to "boost" a previously heated body of water) and compare this peak-rate usage with the extended period the whole tank will be heating over night at the cheap rate.

    I'm sure somone has already done the maths on a 3kw heater re-heating an entire tank from warm (for example) versus heating 1/4 tank (just using top heater) from cold
    :confused: I have a poll / discussion on Economy 7 / 10 off-peak usage (as a % or total) and ways to improve it but I'm not allowed to link to it so have a look on the gas/elec forum if you would like to vote or discuss.:cool:
  • italiaitalia Forumite
    214 posts
    thanks cardew and mute_posting, i realy appreciate your posts

    i have no idea if the bottom tank only comes on at night, if it does then i can't save any money! ill have to see if i can hear it come on.

    thanks for your posts

    im so used to comparing my heating costs to those will gas mine seems high! lol, esp as its only me and i dont put the heating on much.

    i suspect it only comes on over night!
  • CardewCardew Forumite
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    italia wrote: »
    thanks cardew and mute_posting, i realy appreciate your posts

    i have no idea if the bottom tank only comes on at night, if it does then i can't save any money! ill have to see if i can hear it come on.

    thanks for your posts

    im so used to comparing my heating costs to those will gas mine seems high! lol, esp as its only me and i dont put the heating on much.

    i suspect it only comes on over night!

    You really need to find out when your immersion heater and storage heating come on - e.g. how they are wired.

    Is your electricity meter accessible?
  • ronerone Users Awaiting Email Confirmation
    18 posts
    I just want to pipe in and say that I run my immersion heater on a timer for 90 (E7) mins every morning and it gives me two baths worth of water (don't have a shower). I reckon my immersion heater is 1.5kw, costing approx 13p a day to run. I haven't found a way to get cheaper hot water!

    I also run my dishwasher, washing maching and a timed oil heater on E7. (On solid fuel for heating)

    My total electric bill on ecotricity (not cheap) is about £25 a month during winter and £15 a month during summer.

    That said I never use the immersion heater during the day (don't need to) and there are only two of us.
  • espressoespresso Forumite
    16.4K posts
    rone wrote: »
    I just want to pipe in and say that I run my immersion heater on a timer for 90 (E7) mins every morning and it gives me two baths worth of water (don't have a shower). I reckon my immersion heater is 1.5kw, costing approx 13p a day to run. I haven't found a way to get cheaper hot water!

    :confused:

    Are you sure about it being rated at 1.5kW? I have never seen a 1.5kW, the standard ones are all 3kW.
    :doh: Blue text on this forum usually signifies hyperlinks, so click on them!..:wall:
  • CardewCardew Forumite
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    Part of the Furniture 10,000 Posts Name Dropper Rampant Recycler
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    rone wrote: »
    I just want to pipe in and say that I run my immersion heater on a timer for 90 (E7) mins every morning and it gives me two baths worth of water (don't have a shower). I reckon my immersion heater is 1.5kw, costing approx 13p a day to run. I haven't found a way to get cheaper hot water!

    I also run my dishwasher, washing maching and a timed oil heater on E7. (On solid fuel for heating)

    My total electric bill on ecotricity (not cheap) is about £25 a month during winter and £15 a month during summer.

    That said I never use the immersion heater during the day (don't need to) and there are only two of us.

    Agree with espresso that most immersion heaters are 3kW. - I have seen a 2.5kW

    As they have a thermostat it is not possible to know exactly how much electricity they have used.

    So even it it was 3kW and you had it on for 90 mins that doesn't mean that it will use 4.5kWh(any more than 1.5kW for 90 mins will use 2.25kWh)

    However as you say heating water on E7 is about as cheap as you can get. Only a very efficient gas boiler will beat it.
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