Chaufe eau- leave it on, or turn it off?

Water, electricity, gas etc.
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Crazy Diamond
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Chaufe eau- leave it on, or turn it off?

Post by Crazy Diamond »

We’re on a short (5 day) break in Albi which is a truly wonderful city. Before we left I didn’t turn off our water heater which operates using off peak electricity ‘twixt 23.30 and 07.30 as I didn’t think it worthwhile. Thing is I’m never sure what sort of a period of absence warrants turning it off and not wasting money needlessly keeping the water hot. If we’re away for a couple of weeks I switch it off, but for an absence of a few days I don’t bother.
I have always been impressed by the insulation properties of our chaufe eau when hot water has been available when it’s been off for sometime, but would be interested to learn if there’s a cut off point, i.e. more than X days away knock it off, less than that don’t bother. Can anybody please enlighten me?
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Re: Chaufe eau- leave it on, or turn it off?

Post by Aardvark »

Your question is a perennial topic for argument. My personal, unqualified take is: It takes less time=power to keep a well-insulated tank up to temp when nothing is being drawn off, than to let it go cold and heat it from that point. A few days should be fine. I would draw the line at a week or more. For the longer periods I turn off the water at the mains as well.
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Re: Chaufe eau- leave it on, or turn it off?

Post by RobertArthur »

In the past I did try to do some clever calculations, insulation factor, capacity in liters, ambient temperature, cut-off points, algebra etc. I've become lazy or energy efficient with my brains. Rule of thumb now for me: for a modern chauffe-eau électrique, switch off for more than a week absence. A temperature rise from 12 degrees C. to 67 degrees C. and 200 liters will be more expensive (electricity bill) than maintaining it at around 67 degrees C. The modern types with an electronic dispositif anti-corrosion (ACI): don't switch off. You already suspected something like this, so not an in-depth answer to your question I'm afraid. Ten years ago there was an article at the website of THERMOR adressing this issue, not anymore, should have copied it.

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Re: Chaufe eau- leave it on, or turn it off?

Post by Le Démerdeur »

Some of the manufacturers do publish a figure for how much electricity is used just to keep it up to temperature with no water drawn off, something like maintenance consumption but I cant recall the term.

I did the calculation once and like most others who have commented now only switch it off for absences of a week or more.

I came back recently after 7 days away with the BDC switched off, the water was still warm enough to wash your hands or take a quick luke warm shower.

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Re: Chaufe eau- leave it on, or turn it off?

Post by basileus »

A lot must depend on the efficiency of the insulation. So far as I can see french ballons are much better insulated than english hot water cylinders, but my knowledge is very dated,

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Re: Chaufe eau- leave it on, or turn it off?

Post by Hal »

No, I think you are spot on. Insulation gets better by the day and with the water staying hotter longer must make it in favour of just leaving the electricity on excepting long periods of absence.

I leave mine on all the time until we had a couple of days without sun recently when the water cooled noticeably only to find that that stupid little switch they use in France was in the 'O' position! I do miss my UK set-up where there is a big switch on the landing with an equally big red light showing at a glance the status :good: :D

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Re: Chaufe eau- leave it on, or turn it off?

Post by niemeyjt »

RobertArthur wrote:
Sat Oct 12, 2019 9:18 pm
In the past I did try to do some clever calculations, insulation factor, capacity in liters, ambient temperature, cut-off points, algebra etc. I've become lazy or energy efficient with my brains. Rule of thumb now for me: for a modern chauffe-eau électrique, switch off for more than a week absence. A temperature rise from 12 degrees C. to 67 degrees C. and 200 liters will be more expensive (electricity bill) than maintaining it at around 67 degrees C. The modern types with an electronic dispositif anti-corrosion (ACI): don't switch off. You already suspected something like this, so not an in-depth answer to your question I'm afraid. Ten years ago there was an article at the website of THERMOR adressing this issue, not anymore, should have copied it.
Did you bookmark the URL - thermor is archived.

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Re: Chaufe eau- leave it on, or turn it off?

Post by RobertArthur »

@ niemeyjt: I recently cleaned up my gmail, space almost full, so this url is probably lost in action. The same for several hard disks, once almost endless horizons of space. French commercial habits: they do like to rearrange websites every six months (Orange) and throw away useful information, replacing it by easier to read stuff. So chances of survival of an almost 10 year old url are not too rosy. In the past I've been able to recover information from websites as Entraidelec (French electrical code) thanks to webarchive.org. They do safe a lot, but use a sampling method, so not every day in the life of a website is available.

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Re: Chaufe eau- leave it on, or turn it off?

Post by Fitter »

We stopped using the heures creuse system to switch our ballon on and off and just switch it on manually for 3 or four hours every other day.
This resulted in a huge reduction in electricity usage and still got as much hot water as needed.
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Re: Chaufe eau- leave it on, or turn it off?

Post by just a Frenchie »

Aardvark wrote:
Sat Oct 12, 2019 8:59 pm
Your question is a perennial topic for argument. My personal, unqualified take is: It takes less time=power to keep a well-insulated tank up to temp when nothing is being drawn off, than to let it go cold and heat it from that point. A few days should be fine. I would draw the line at a week or more. For the longer periods I turn off the water at the mains as well.
I value Aardvark's post: for a few days, don't swicth it off. Over 1 week, it might be worth switching it off... But, be careful in winter if it can be freezing cold indoors: the tank might burst. I've never seen a capability of keeping a minimum power to prevent freezing of a hot water tank with a * on the knob like on radiators. When I was a multipurpose builder, I've often been asked by estate agents to empty tanks of empty flats before winter because the mains were stopped in empty flats. What a waste of water ! And, when you re-fill them, the mud in the tank is stired and gives a brown colour to the water until it settles down...
You learn from your mistakes but it's much quicker and cheaper to learn from the mistakes of other people ! :D

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