Any electrical whizzes?

RutlandMike

RutlandMike

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Here's a question and some may think it's really stupid but here goes - does an immersion heater use less power coming on twice a day (between which water cools and needs re-heating) or if it's left on all the time - obviously with a thermostat. I think it's cheaper twice a day but not sure now I come to think of it.
 
It will work out cheaper twice a day as the heat loss from the tank is proprietorial to the temperature differential ie the hotter the tank the faster it will loose heat.

Its all down to heat loss from tank rather then the immersion heater
 
Impossible to answer as it depends on
1. The power rating of your heater
2. The size of the tank
3. The efficiency of the insulation.
and last but not least 4. The amount of water you draw from the tank and when you do it.
 
it's not impossible to answer and it doesn't depend on any of those things! it is cheaper to come on twice a day, as the heat loss will be less during the day because the tank is cooler
 
OK, good points. For the sake of the discussion, lets assume that the tank capacity is 100 litres, a 1kw heater, water temperature drops by 25 degrees between heating cycles and nothing is drawn from the tank between heating cycles. Any ideas?
 
1. if you're not drawing hot water, switch it off.
2. are both proposed heating periods charged at the same rate?
3. if there's a loss, get better insulation - a 'white meter' heated tank will retain until the next cycle including some use. A boat calorifier will still be reasonably warm next morning.
Ie - one cycle per day. - tweek the thermostat to required temp.
 
KevinMac is absolutely right - twice a day is cheaper. The only assumption he has made is that we are discussing the same system - it doesn't matter about the size of tank, amount of insulation, amount of water used etc as these factors are constant.
In essence, a tank which is kept at a constant high temperature will lose more heat more rapidly than one which is allowed to cool off twice a day. Not Einstein but Newton.
 
This is an old chestnut - it is ALWAYS cheaper to turn off an electric immersion heater.

The same is true of your central heating - it is often suggested that the cost of bringing the house back up to temperature means that it is cheaper to leave the heating on - not so. You save massively by turning off the heating.

Another chestnut - it is cheaper to leave a fluorescent lamp on than turn it off? No, turn it off if you are going to be out of the room for more than 10 minutes or so.

You save electricity by turning off your nav lights at night. Yes, but only murderous idiots do that. Sadly, quite a lot of murderous idiots. Spread the word and save some lives.
 
Excellent advice all, many thanks - I kind of thought so but some smart arse in the pub last night was adamant that it's cheaper to keep it on..... I'm off for a timer!
 
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Another chestnut - it is cheaper to leave a fluorescent lamp on than turn it off? No, turn it off if you are going to be out of the room for more than 10 minutes or so.

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A few years back I did some measurement on this. IIRC the additional energy used in switching the light on was equivalent to leaving the lamp on for about 20 seconds.

However, you also need to take account of the reduction in the lamp's life expectancy casued by repeated switching on and off.

John
 
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I'm off for a timer!

[/ QUOTE ] And also look at the possiblity of a day and night rate tariff for your power supply. If you can use the water heater during an off peak time and put the dishwasher and washing machine on timers to operate overnight there may be further potential for savings.
 
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