Immersion heater running costs

  Chris the Ancient 15:45 04 Dec 2009

Well off the topic of computers, I know.

I live in an 'electric only' flat with water heated, in a pressurised system, by immersion heater(s).

My 'best-use' knowledge of these possibly precludes me from using it in the most cost-effective manner.

I do not use a lot of hot water in a 24 hour period. A nice powerful shower in the morning and bits of washing up during the weekday. At weekends, the consumption is higher because of the week's laundry and car washing (I use a bit of hot water in the car was bucket coz I'm a wimp).

So, to be cost-effective, should I leave the off-peak immersion on all the time and keep a whole tank-full of water (unnecessarily) hot. Or, should I use the top-up heater (that seemingly heats the just the top half of the tank) on an occasional basis - accepting that it uses peak rate electricity?

Or a mixture depending whether it is weekday ar weekend?


  Chegs ®™ 15:57 04 Dec 2009

Have a look on iPlayer at the "Bang goes the theory" program before deciding what to do.

After you've watched it,there are several hints & tips on the website to save you some cash on energy costs.

  Chris the Ancient 16:07 04 Dec 2009

Just had a hunt in there, but can't find anything on immersions. Am I missing it?


  Chris the Ancient 16:10 04 Dec 2009

click here

But nobody mentions off-peak!

  peter99co 16:14 04 Dec 2009

I use an immersion heater and set it to 1 hour on during Economy 7 period 6.00 to 7.00. A 1/2 hour on at 18.00 gives all the hot I need.

The shower uses the available hop water, it is not reheated by any other means.

If we are out for the weekend it is switched off.
It has a boost button but this is rarely used.

The washer is used on economy 7 as often as reqd.

I have a friend who uses a dishwasher on a timer so it uses economy 7 as well. He does not run it until it is a full load.

  Chris the Ancient 16:20 04 Dec 2009

Unfortunately (?) my off peak is 23:00 - 07:00 with no real chance of being able to, maybe, put in a timer switch (being rented accommodation).

I presume your boost button runs a 'top-half' heater like my top-half heater.


  bri-an 16:26 04 Dec 2009

"The shower uses the available hop water.."

I like the idea, washing in beer..? (;-)

  peter99co 16:31 04 Dec 2009

I fitted my own (shop bought immersion heater/timer) and had it checked by an electrician. It replaced an ordinary (high amperage) switch. It is only two wires in and two wires out after all. The cost of the switch may need checking out though. It may be worth asking the landlord for permission or maybe to upgrade for you.

  peter99co 16:35 04 Dec 2009

click here heater timer&source=15

Electronic Immersion Heater Time Controller
only £29.99

  Chris the Ancient 16:49 04 Dec 2009

Some interesting ideas there.

But... I'm still not sure on the cost-effectiveness, or not, of whether keeping the hot 'topped up' - or not is best.


  namtas 17:14 04 Dec 2009

It can be easily calculated if you know the size of your immersion, the initial water temperature and the final temperature.

It takes 4.184 Joules to raise 1 gram of water by 1C
Start temperature of water is about 10C
End temperature is about 70c
1 Litre of pure water is 1kg = 1000grams
Size of tank = 100 litres?

We want to raise 100000 grams of water by 60C
This will take 418400 x 60 = 25104000 Joules

A Joule is the work done to produce power of one watt continuously for one second, or 2.7778 ×10?7 Kilowatt-hours.

So to heat your tank from cold, it will take about 6.97kWh

Compare this to how much heat we lose with an immersion left on.

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