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Leave on permanently or use a timeswitch


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On a standard tariff you may as well leave it on all the time as there is no economy to be made.

If however you are close to the limit of your abonnement and sometimes trip the disjoncteur d'abonnement you may wish to consider heating the cylinder during the night to reduce the incidence of tripping during the day, 5.5 hours is all it takes to heat up a ballon however if its on a timer and you use all the hot water you either have to wait till the next day or switch it over to marche forcé.

If a lot of people may be taking baths showers at peak times then a timer will be a    disadvantage.

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I inherited a 200 litre water heater when I moved into my current apartment, which is far too large for a single person (50 L normally recommended) and I would change it but for the fact I am selling up and moving to my nearby town. I have always left the heater On, on the ground it is only heating up the (small amount of) water I use, whereas if I switched it Off the water would cool and require re-heating. I hope this sounds logical! But as suggested, if you are a large family and drain the tank, best to use the 'cheap rate' period to re-heat. If you are re-plumbing you can get small water heaters (50 L or less) to have a separate supply for the kitchen, say, or a shower. This may work out even more economical........and easier to plumb. I am investigating the options for my new place. Hope this helps  a bit.

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On off or trickle feed?

 

By analogy with under floor heating, 2 engineers in 2 different countries told me tat the night time control temperature should not be too far removed from the day time set point, to avoid the boiler having to do too much work on start up and using too much fuel.

By analogy therefore trickle feeding the tank by leaving it permenantly on would be the best way to go.

 

However, my O level physics tells me that the rate of heat loss is proportional to the temperature difference.

So as the temperature in the tank drops less heat is lost.  In fact if the cylinder is in a cupboard then not only do you benefit because the tank is cooler, but that heat goes into the air around the tank and warms it up - so you have a balancing of temperatures.  This would suggest that an on-off policy should be preferable.

 

So now I am as confused as the OP and can only say, ours stays on all of the time.

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Leave it on (unless as someone said you are in danger of tripping the switch)

I've said this before, but basically an old next door neighbour used to have her hot water and heating on timed and wondered why her bills were more than mine, when our boilers were the same. We left ours on all the time, sometimes low admitedly but it meant the system was never reheating from cold.

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The best way is to test it for yourself. Take a meter reading and go through the same bathing and washing up cycle for a couple of days, one on constant and one on timed and note the meter readings.

I noticed only a very slight difference in favour of turning it on and off but that was with just me in the house, with a house full it went the other way and leaving on constant was more efficient.

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I installed exactly the same in April 2011 and am also on flat rate electricity.

I ran it through an energy consumption meter and a timer from the beginning and had it coming on for 2 hours per night between 4 and 6AM.

Between then and now, even with 6 or more people in the house last Summer, we have never once run out of hot water - even in the evening - and it has cost me €10/mth to run so the idea of leaving it on 24/7 does not make any sense for me and can only cost me money.

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Ernst, out of curiosity have you run it 24/7 just to compare energy usage?  on my little test the results were surprisingly close.  Back in my student days we shared a flat and the same discussion took place with the immersion heater. When I ran the test then leaving it on constant was using nearly double the electricity. 
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Perhaps it depends on how many times you heat up from cold, and the insulation of the tank.?

In this house ( 4 adults) there are showers run literally morning noon and night. If there would be enough hot water at 9pm from a early morning heating I can see that might work ( although actually I don't think our tank is large enough to cope with that )

I have to say that the neighbour who had higher bills was heating up from cold twice a day, so that would be a factor too.

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So leaving it on whilst absent for two weeks is much more expensive that re-heating from scratch (5hrs) when returning to the house ?

Also, should we have consider some king of temp control as the water that comes out is hot enough to boil an egg! (it's a new 200l Atlantic)..

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[quote user="joidevie"]So leaving it on whilst absent for two weeks is much more expensive that re-heating from scratch (5hrs) when returning to the house ?

Also, should we have consider some king of temp control as the water that comes out is hot enough to boil an egg! (it's a new 200l Atlantic)..



[/quote]

Yes to the first question and the second isn't true, you couldn't boil an egg in 63 degree water but it would probably still cook.  The french regs state the water must reach that temperature to kill bacteria in under 30 seconds, setting the temp lower may cause you to get ill so don't do it. Instead connect a temperature limiting mixer device under the sink so the water comes out at a maximum of 43 deg.

UK version shown.

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[quote user="Théière"]Ernst, out of curiosity have you run it 24/7 just to compare energy usage?[/quote]No I haven't and I'm not sure I can be bothered to repeat the exercise and put the effort into comparing.

Frankly even if it did save me a couple of Euros a month thankfully I haven't yet got to the stage of micro managing my finances to that level - and I hope I never do !

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[quote user="Pommier"]Have a look at the thermostat on the chauffe eau. Does it look like this? http://yfrog.com/f3dsc0916lj If it's set on 5 that's the highest temperature, so try turning it down to 3 or 4.[/quote]

Great info from all again, and this temp control setting pic..

So, is the consensus that on a normal tariff that say a 200l tank with 2 showers a day (maybe 3 if there's a visitor), and only with a little kitchen use (we have a dishwasher), that say two of hours of 'on' time (via a timer) is noticeably cheaper to run?

And what type of timer is recommended and where it's wired in? And are there normes about where the 'timer' is located?

Many thanks again..

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It's my understanding that chauffe eau are lower powered than UK immersion heaters (because lots of people only have eg 6kw of supply) so I think it would take longer than 2 hours to heat the water. I'd experiment with 3 or 4 hours.

If you're resident in France have you considered paying the slightly higher standing charge and having heures creuses - you can then fit a connection into your fusebox to automatically switch on (and off) the chauffe eau.

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Don't remember what capacity my tank is but it actually has a plate on it that says it takes 5.5 hours to heat it from cold to hot - well it does specify temperatures but I don't remember the details, I just remember the 5.5 hours.

I have tried it both ways and it is far cheaper to heat it up as required. 5.5 hours every other day is ample for showers, washing up etc, and when there's only me here it sometimes lasts 3 days. If left on all the time it seems to cut in quite frequently for the odd quarter of an hour or so.

At our 'second home' in Wales we have a much smaller tank, set to heat up twice a day for a couple of hours at a time on the Economy7 tariff, and there never seems to be enough hot water.
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I have experimented over the years and I have found that unless the tank stands cold for a significant time it is more economical to leave the water heating on all the time. Mind you I have a well insulatedtank which might affect the results
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[quote user="Rabbie"]I have experimented over the years and I have found that unless the tank stands cold for a significant time it is more economical to leave the water heating on all the time. Mind you I have a well insulatedtank which might affect the results[/quote]

So does the number of times you shower [:P]

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[quote user="Théière"]

[quote user="Rabbie"]I have experimented over the years and I have found that unless the tank stands cold for a significant time it is more economical to leave the water heating on all the time. Mind you I have a well insulatedtank which might affect the results[/quote]

So does the number of times you shower [:P]

[/quote]Provided you use the same amount of hot water while comparing the two options I don't see whether I shower 1 time or ten makes any difference.

The basic maths is quite simple. You use the same amount of energy to heat water at the input temperature up to the temperature you have your tank thermostat set to. The main advantage of always on is that if there is a sudden demand for hot water you don't have to wait to your preset time  to heat some more.

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Hi -

Slightly off topic, but when we renovated our shower room/loo some seven years ago, my French plumber friend advised on putting in a small electric water heater with a capacity of only 30ltrs. I said, no, I would need one of about 100ltrs at least.

He gave me an old fashioned look and said: "A large tank will need hours to heat up. With a 30ltr tank, you arrive at the cottage and the first thing you do is turn the water on and then the electricity. By the time you have unpacked the car the water will be hot."

When I said that having only 30ltrs of hot water would not be enough, he (with the patience of someone dealing with a child) said: "Ah! But when you shower, the water is so hot you will only use about 7 to 10 ltrs of hot water mixed with about 20 - 30 of cold." And he was right! The tank heats up quickly and we can get three adult showers from a full tank.

As for leaving it on all the time, I have pondered this question (and even posed it on this forum somewhere), but have never got round to trying the timer method against 24/7 and it is the latter we use unless we are away for a few days. I'd be interested to hear any comments about the pro's & con's of this with a smaller tank like ours.

Cheers!
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