Hot water cylinder

I have just moved into a new house with an electric unvented hot water system The hot water cylinder has 2 immersion heaters and is fully insulated.
My question is: what is the best way to use the system. If I use the timer to switch it on for a couple of hours a day I run the risk of running out of hot water (it runs the shower too). Will it be a lot more expensive just to leave it on 24 hours a day? The water seems to stay hot when not used so presumably it won't be using much power?
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On Sun, 14 Sep 2003 11:20:09 +0100, Ade wrote:

The bottom heater should come on overnight, when you're on cheap rate electriricty. That way you get a tank full of hot water on cheap rate. (You are on E7 or a similar cheap night-rate tariff, aren't you?) The top heater is intended for manual day-time boosts if you start running out of hot water. In the end, it's down to you and how you want to use the water.
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Thanks, this place has just been built and has a 'single tariff' and only one reading on the meter. There is no gas here and the heating is simple electric heaters similar to Travel Inns. I know it's a fairly expensive way of doing it but I was just wondering whether it is worth trying to restrict the amount of time the immersion is on because it is thermostated to 60 degrees so if the cylinder (170 litres) is insulated it shouldn't use more than a few pence a day to keep it hot if it isn't used? Or should that be pounds?
On Sun, 14 Sep 2003 14:25:35 +0100, "Owain"

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"Ade" wrote [top posting corrected] | "Owain" wrote: | >Provided the thermostats are working and are correctly set, it shouldn't be | >much more expensive to leave it on all day. | Thanks, this place has just been built and has a 'single tariff' and | only one reading on the meter. There is no gas here and the heating is | simple electric heaters similar to Travel Inns.
The good news is that as a new property the insulation should be fairly good. I wouldn't worry too much about leaving the immersion on overnight. But you could take night and morning readings on the meter for one week with the immersion on and the following week with it off, and see if there's a significant difference.
Either way, you can get an Economy 7 style timeswitch that will control the 2 elements[1]
The bad news is that those little electric heaters are going to start costing you money when the weather gets colder. You could consider changing them to storage heaters (lounge, bedroom, hall). They are rather bulkier than panel heaters, but because the elements are inside the bricks you won't get the smell of hot dust that the panel heaters are prone to.
If the electric heaters each have their own circuit back to the CU you would not have to rewire them; replace the fused connection unit on each one with a timeswitch[2] set to the Economy 7 cheap rate period and swap the panel heater for a storage heater[3].
You probably already have a dual-rate electronic meter, so the electric co would simply program that to register peak and off-peak separately and might fit a timeswitch or teleswitch. This would be a small box that connects to the meter with light-gauge wiring.
You could also put your washing machine on the timeswitch, especially if it is cold fill and the rumble-slosh noises don't keep you awake.
Comparison of Economy 7 tariff - from telecomplus - this was the first one that came up on google.
Standard Annual Standing Charge 24.29 Unit Rate (pence) 5.52
Economy 7 Annual Standing Charge 54.76 Day Rate (pence) 5.97 Night Rate (pence) 2.40
I would suggest you do some weekly meter-reading with a note of about how much you have the heating on for the next couple of months as it gets cooler, and you would then be able to work out whether it would be worth changing to Economy 7 and doing so before it gets really cold.
Owain
[1] http://www.tlc-direct.co.uk/Products/HOELEC7.html
[2] Timeswitch. You must ensure these are kept set within the Economy 7 period, as they will not themselves keep synchronised with the electricty co's timeswitch that changes the meter from peak to off-peak.
24-hour fused spur timeswitch http://www.tlc-direct.co.uk/Products/SMFST11.html
[3] Storage heater but check local suppliers as these are heavy. http://www.tlc-direct.co.uk/Main_Index/Heating_Index/Storage_Heaters/index.h tml
3.4 kW storage heater http://www.tlc-direct.co.uk/Products/UNWMS724.html
ditto including convection heater http://www.tlc-direct.co.uk/Products/UNWMC724.html
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Thanks Owain. I have started taking readings and will compare them over a week with and without the immersion heaters on 24 hours. As for the electric heaters - the place is extremely well insulated (being a flat that needed extra insulation for traffic noise to get planning permission) and if it works out as expected the room heating shouldn't be a problem. We used to be in a place with night storage heating and I didn't like it because they always ran out of heat around by 9pm and didn't have an override switch.
Kevin
On Sun, 14 Sep 2003 21:24:38 +0100, "Owain"

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"Ade" wrote | Thanks Owain. I have started taking readings and will compare them | over a week with and without the immersion heaters on 24 hours. As for | the electric heaters - the place is extremely well insulated (being a | flat that needed extra insulation for traffic noise to get planning | permission) and if it works out as expected the room heating shouldn't | be a problem. We used to be in a place with night storage heating and | I didn't like it because they always ran out of heat around by 9pm and | didn't have an override switch.
Even if you decide not to go for storage heating (and I do understand why) you could replace some of the FCUs with timer ones to give you additional control.
Owain
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