Cheapest way to use the immersion heater

A question about : Cheapest way to use the immersion heater

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:

Best answers:

• He was right.......leave it on.
  save a little by turning the thermostat control down a touch........no-one will notice
• Just understand and remember the following: "The rate of loss of heat is proportional to the temperature differential" and you have your answer!
• 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.
• 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)?
• 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,
  TRAF SEE ME!!!
• 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.
• 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 Ј50 to Ј100, 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.
• 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.
• Thanks for the reply, I'm not sure I would trust myself or the boyf to start fiddling with the heater (and its so old I bet it is corroded) plus its in an awkward place to get to (as I discovered whilst merrily piling blankets on top of it this weeked) but it is something to bear in mind.
  I own the flat (no landlord to ask!) so I sometimes wonder if it would add value at all to eventually take out the immersion and put a boiler and central heating in like next door have done (it gets very cold in winter with only that stupid coal effect gas fire in the main room, you can imagine the bathroom and kitchen...). I would need to save up for that though, I know we're talking thousands. I remember when I bought the flat the lack of central heating was one of the things that put me off a bit, what do you think, is it worth saving up for?
  ETA: re boiling a kettle, I do sometimes but get peed off boiling it again and again (lazy I know but I like the water to be properly hot so end up boiling a few).
• Bestyman, I was referring to Dual -Element immersion heaters, one short and one long element combined, that only require one boss on the top of the tank.
  Santon used to do one with a switch on the top labelled "Bath" on one side and "Basin" for the other switch position.
  The modern versions seem to be aimed at Economy 7 users, or electronic timers, but I dont see why they cannot be used with a simple suitably rated manual changeover switch.( 3kw= 13 amp). They had been replaced over time, by two seperate short side mounted heaters, but seem to be making a comeback. I have seen a lot of ads for new properties highlighting the fact that the hot water tank has a dual element heater.
  Badgergal, try this for replacing immersion heater, (diy,) that is if you find one that suits (Ј40ish).
  https://www.readersdigest.co.uk/diy/webpages/340_341.htm
  and to help with energy saving,
  https://www.iee.org/Policy/Areas/EnvEnergy/saveitnew.pdf
  Re central heating a small combi might do and the bits should be a little less than one thousand, its the installation that costs, unless you can persuade boyfriend to become Corgi registered as well.
  HTHs Scat
• Switching the immersion heater off is cheaper, but if the tank's well lagged, only by a few pence per year!
• Instead of getting a gas boiler you could buy a couple of used storage heaters and have your electric meter swapped for an economy 7 one. The tank of water would be heated in night and you would have heating in the cold weather. We have storage heaters and live in an old 3 bed detached and our home is toasty in winter, we have plenty of hot water and use washer etc in the cheap time. Our bill is Ј50 a month which I do not find too dear.
• Don`t go for electric storage heaters. They are the most inefficient & expensive means of heating.
• Old duvet down sides and over top really made a difference to our already insulated tank.
  Also, I've trained children and OH not to run off loads of hot water just to rinse hands. Our tank is downstairs and it takes ages to get the hot taps upstairs to run hot. Usually we turned on hot tap and rinsed hands in the cold bit and had finished before the hot come through, but tank is then being filled with cold water. Using the cold tap really maks no difference.
  Of course I let them use the hot for proper washes!! lol
• My dad decorated the whole house - right through - lovely. Then he moved the tank in the bathroom, installed new suite etc. All finished.
  Next evening mum switched emersion on - BANG! Thought it was a fire work. Then thought it was mums cooking.
  Result - three fire engins. No house!! Just a shell, but all safe.
  Be careful!
• 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