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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 2
  • gnilsson
    Hi,

    I've been reading this thread with interest and have some questions. We have recently moved from a house with a convection (?) hearter i.e. one that heats water as it's used to one with a boiler, pump, etc. At present, the hot water does not last for two reasonable length showers and this is a bit of a shock for us. The water tank does seem to have an immersion heater, but this is also something new to me so I'm not quite sure how I can tweak my system to give us the amount of hot water we want. Does anyone have any tips for how to ensure we have more hot water than we currently do? What are the limitations on how much hot water you can have, etc? Any tips around this topic that anyone can provide would be greatly appreciated.

    Many thanks,

    Gustaf
    • Cardew
    • By Cardew 4th Mar 08, 4:59 PM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    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.
    • italia
    • By italia 5th Apr 08, 11:53 PM
    • 211 Posts
    • 37 Thanks
    italia
    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 ????
    • Cardew
    • By Cardew 6th Apr 08, 8:27 AM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    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.
  • mute_posting
    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.
    .
    Originally posted by Cardew

    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
  • mute_posting
    3) leave it off all together and switch the top (boost) emersion on 20 mins before my shower?
    Originally posted by italia
    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
    • italia
    • By italia 6th Apr 08, 4:30 PM
    • 211 Posts
    • 37 Thanks
    italia
    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!
    • Cardew
    • By Cardew 6th Apr 08, 6:42 PM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    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!
    Originally posted by italia
    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?
    • rone
    • By rone 9th Apr 08, 7:18 AM
    • 18 Posts
    • 3 Thanks
    rone
    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.
  • espresso
    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!
    Originally posted by rone
    :confused:

    Are you sure about it being rated at 1.5kW? I have never seen a 1.5kW, the standard ones are all 3kW.
    Blue text on this forum usually signifies hyperlinks, so click on them!..
    • Cardew
    • By Cardew 9th Apr 08, 9:22 AM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    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.
    Originally posted by rone
    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.
    • rone
    • By rone 9th Apr 08, 10:23 AM
    • 18 Posts
    • 3 Thanks
    rone
    Defo 1.5KW.

    I've measured it by virtue of making sure nothing is running other than immersion heater and seeing what is consumes over 90mins for that particular part of the day.

    Plus, even if it's thermostatic you can base your measurment of an upper limit of what it would consume if it was driving all the power all the time, your real world would be less, which is no bad thing eh?

    Can't argue with my bill, and I don't have much choice as we can't have gas.
    • Cardew
    • By Cardew 9th Apr 08, 11:32 AM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    Defo 1.5KW.

    I've measured it by virtue of making sure nothing is running other than immersion heater and seeing what is consumes over 90mins for that particular part of the day.

    Plus, even if it's thermostatic you can base your measurment of an upper limit of what it would consume if it was driving all the power all the time, your real world would be less, which is no bad thing eh?

    Can't argue with my bill, and I don't have much choice as we can't have gas.
    Originally posted by rone
    That certainly does not mean it is "defo 1.5kW"

    It might only use 2.25kWh over 90 minutes, but if it was 3kW it could be only heating for 45 mins. The average is 1.5kWh consumption for that 90 min 'test'.

    Put it this way. Mine is certainly 3kW. If I leave it on for 24 hours and it uses 2.4kWh that doesn't make it a 0.1kW (100 Watts) heater. It means it has been heating for 0.8 hours in the 24 hour period.

    I suspect if you left it on for 90 mins and during that time were using lots of hot water, you would use a lot more electricity.
    Last edited by Cardew; 09-04-2008 at 11:36 AM.
    • rone
    • By rone 9th Apr 08, 12:37 PM
    • 18 Posts
    • 3 Thanks
    rone
    That certainly does not mean it is "defo 1.5kW"
    Originally posted by Cardew
    I completely understand what you're saying and I take your point but the "defo" bit comes from the fact that I seem to remember metering it.

    In terms of kWh I was able to equate the usage over time to the cost which happened to equal what the meter was reading, hence I gathered - from cold it was consuming 1.5kW for the duration of time it was on.

    Also, 24hrs is a much broader comparison, it doesn't equate to the same average on a 90 minute "from cold" useage which I suspect will be close to full load for most of the time.

    But I will double check, because you've got me questioning myself.
    • Cardew
    • By Cardew 9th Apr 08, 1:57 PM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    If you can get to look at your immersion heater it will have the rating on the top cover.

    The other way to test will be switch it on when water tank is cold, check the meter, and then check again after 20 mins - if it is 3kW it will have used 1 unit.

    I only gave the 24 hr example to illustrate the point.
  • stevemof
    7Kw or 4Kw?

    I want to fit an immersion heater and the most useful setup would seem to be to have it on a timer. The cheapest route is a plug in timer, which would restrict me to a 3Kw heater. Anything bigger could not be used with a simple plug in timer.

    Is 3Kw worth using? Are they any good?
    • Cardew
    • By Cardew 1st Jan 09, 9:00 PM
    • 28,022 Posts
    • 13,866 Thanks
    Cardew
    7Kw or 4Kw?

    I want to fit an immersion heater and the most useful setup would seem to be to have it on a timer. The cheapest route is a plug in timer, which would restrict me to a 3Kw heater. Anything bigger could not be used with a simple plug in timer.

    Is 3Kw worth using? Are they any good?
    Originally posted by stevemof
    I have never heard of a domestic immersion heater bigger than 3kW and yes they are more than adequate.
  • Dinx
    hi, I am just new to this place. and punched in google and came across this place.

    I have a 2 rate meter and currently we use the gas boiler to heat the hot water and heating, currently everything turns on at night from mobile phone chargers to even the cordless house phones. I just found out the hot water tank also has a electric immersion heater at the top. we have a big house hold.
    would it be effective to use the immersion heater at night or just stick with the boiler. the boiler right now turns on just for two hours to warm up the house a little and give us hot water. but during the hot summertime we only turn our boiler on for hot water only. and of course during winter its on its lowest setting and left on all day long. so If I turned the immersion heater on for the 7 hours during the night would that be better or just stick to the boiler.
    • Magentasue
    • By Magentasue 30th Apr 09, 10:09 AM
    • 4,201 Posts
    • 2,671 Thanks
    Magentasue
    hi, I am just new to this place. and punched in google and came across this place.

    I have a 2 rate meter and currently we use the gas boiler to heat the hot water and heating, currently everything turns on at night from mobile phone chargers to even the cordless house phones. I just found out the hot water tank also has a electric immersion heater at the top. we have a big house hold.
    would it be effective to use the immersion heater at night or just stick with the boiler. the boiler right now turns on just for two hours to warm up the house a little and give us hot water. but during the hot summertime we only turn our boiler on for hot water only. and of course during winter its on its lowest setting and left on all day long. so If I turned the immersion heater on for the 7 hours during the night would that be better or just stick to the boiler.
    Originally posted by Dinx
    It would almost certainly be cheaper to use gas to heat your water. Can I ask why your are on Economy 7 if you have gas? On some tariffs you need to be using more than 50% of your electricity at night to make this tariff pay and this is almost impossible to achieve without electric storage heating.
  • Dinx
    reading around other websites they say at least 30% needs to be used during the night. and I average around 29- 31% use during the night. for a 3 bedroom house with 5 people living inside we only spend 25 direct debit and the account is in credit of over 130.

    using the immersion heater would be consider as a waste then?
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