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I'm doing some work at a property that has off peak storage heaters & immersion heater. The old lady has just moved in, and are trying to understand how Economy 7 functions. None of my work involves the off peak supply.

My understanding was that the only circuits to benefit from the off peak supply, were those circuits directly connected to the off peak CU, and then to the dual tariff meter.

However, I've been reading on some of the suppliers web sites, stating 'use plug-in or in-built timers to set your electrical appliances like washing machines, tumble dryers and dishwashers to come on overnight – while you’re on the cheaper rate', which suggests to me that RFC's, lighting circuits etc, connected to the standard rate CU, will also use the cheaper off peak rate overnight?

Bit of a dumb arse question, but I'd always thought it was only the circuits connected to off peak CU/meter, that had the cheaper electric overnight :oops:
 
Economy 7 changes the whole installation over to low rate and also can provide a separate switched supply.
whereas an off peak supply is one which only turns on a separate supply on the low rate.
 
Thanks Dave. I've told my customer to enquire as to what tariff their on, in this case they have two separate feeds from the meter to two separate CU's, one for storage heaters etc, the other for standard circuits (RFC's etc).

So if their tariff was off peak, only the storage heaters would benefit from cheaper electricity, whereas if they were on Economy 7 both CU's would benefit from cheaper electricity at the appropriate time at night?

Whilst I was there, I noted that the lowest heating element on the immersion (which I believe is normally for the cheapest rate) came on around 3pm, which I thought was related to an Economy 10 tariff? (sort off afternoon boost).
 
I think you can have an afternoon boost in any system, it all depends on how it is set up and controlled.
My house is on economy 7 controlled by a radio teleswitch without a boost.
I think an off peak supply would normally have a timeswitch controlling it
 
Cheers, I think this install is like yours with the teleswitch (there's no time switch just the meter), except they seem to have some afternoon boost.

Learn something every day :)
 
PS do you use the meter to time the use of the immersion heater (lower element) of do you use some form of time switch (i.e. leave it for the full overnight hours)?
 
PS do you use the meter to time the use of the immersion heater (lower element) of do you use some form of time switch (i.e. leave it for the full overnight hours)?
The off peak element is connected (if it has 2) to the dedicated off peak CU, the other will be on the 24hrs supply, as Dave said the whole installation (24hr CU) will go over to off peak rate too. At the low tariff times.
 
PS do you use the meter to time the use of the immersion heater (lower element) of do you use some form of time switch (i.e. leave it for the full overnight hours)?

It looks like the E7 was an afterthought in this house as the storage heater supply is entirely surface wiring along the skirting board and there's only one supply to the immersion (24hr) despite being a dual element type cylinder
So I have added a timeswitch to the immersion myself (don't tell my landlord!) to bring it on during the E7 hours
Normally you'd have the bottom immersion heater on an E7 supply and the top (boost) element on a 24hr supply.
 
When I confirmed my visit to site yesterday (to install luminaire), the customer's daughter now looking at a time switch to be installed for the on peak immersion. They have an economy 7 cylinder, with 2 x immersion. It appears the lower immersion (off peak) is not working, further investigation. Her mother is using the upper (standard rate) to heat water, but forgets to turn it off.

From my research, it appears with an economy 7/10 tariff, the off peak tariff is considerable cheaper, but any electricity used outside that tariff is more expensive than normal? So using the standard rate to heat water, would be expensive.

It seems installing a time switch, like Horstmann Quartz/Electronic Economy 7 Timer to the 24hr immersion FCU, and have the timer set for when the Economy 7/10 times function and boost function outside those times, would be the more economical solution. Does that seem correct?

If a timer is connected to the off peak FCU, not sure how they retain settings/ times without constant supply, although the manufacturer suggests 150hr internal battery reserve.
 
Surely the best solution is to get the bottom (off peak) immersion heater repaired/replaced and just use the top heater for its intended purpose as an occasional top-up when required. Then maybe install a 1 hour timer to the top heater so the customer doesn't need to remember turn it off. My guess is that, as there's only one occupant, if the bottom heater worked, and heated the whole tank at off-peak rate, the top heater would generally not be needed.
 
if you had a dual tariff meter installed, then everything in the house would be on cheap rate 12 midnight till 7 am.
 
Thanks for the replies chaps, bit of an Economy 7 newbie. Will find out why the bottom element isn't working.

I've asked the daughter to find out what tariff they're on, so we can decide what best to do. As you've all said, most economical would be to use the cheaper rate to heat the hot water overnight. I was just wondering whether to use the teleswitch to operate the timings. I did read somewhere that operating any immersion for 7 or 8 hours (overnight) was uneconomical, whatever tariff you use. Suggestion was to reduce the 'on' time with some sort of timer, with the option of a boost during the day.

It would appear that Economy 10 has a couple of hours in the evening, small hours & a few in the afternoon. I think they have that tariff.

For the record, the Horstmann timer I mentioned, requires constant supply to function. It's to be installed on a permanent supply, and can reduce the hours 'on', during the cheap rate hours. They do another controller (BX2000), which both cheap rate/standard rate supplies to twin/dual immersion. The only benefit, is it will override any selected 'boost', to use cheap rate times. But it's not cheap.

Think I'll suggest just having the off peak FCU, left permanently on, with a Timeguard boost timer or similar for the standard rate FCU, so they don't have to worry about turning it off.

Thanks for the assistance. :)
 
If you have a properly (factory) insulated tank, it shouldn't make that much difference if the bottom element is on for the full 7 hours. It has a thermostat so will not demand when it is up to temperature.
If the mother continually uses the top element and forgets to turn it off, reducing the temperature setting on it's thermostat will cut costs
 
Cheers, tanks modern with standard foam insulation. Piece I read, quoting all sorts of facts & boring figures, suggested pointless keeping topping up to 60' all night, but get your point.

The ole dears been leaving it on all day. Think you have to keep temp at 60' thereabouts, to prevent nasty bugs forming, and the Economy 7/10 standard rate, is a bit pricier that normal standard, so one needs to be careful.
 
If you have a properly (factory) insulated tank, it shouldn't make that much difference if the bottom element is on for the full 7 hours. It has a thermostat so will not demand when it is up to temperature.
If the mother continually uses the top element and forgets to turn it off, reducing the temperature setting on it's thermostat will cut costs
Totally agree. The key to economy is not to put a timer on the cheap rate heater, but to ensure that the insulation of the cylinder and, to a lesser extent, the hot water pipework near the cylinder, is up to scratch. If you feel the outside of a well insulated hot water cylinder, you can hardly feel any heat coming off it.
 
Went to the property today. The son-in-law has been on to their supplier. The lady has three different tariffs, none of them cheap rate. So they are looking at their options.

The 'off peak' immersion element is toast. So over to a plumber, not getting my hands wet! In meantime, will fit them a boost switch for the standard rate immersion, so she doesn't have to worry about turning it off.
 
Remember the bottom element, off peak, heats the whole tank.

The "boost" top element only heats the top 1/3rd or so of the tank.

So wiring the top element to off peak means the customer runs out of hot water mid morning!!
 
Remember the bottom element, off peak, heats the whole tank.

The "boost" top element only heats the top 1/3rd or so of the tank.

So wiring the top element to off peak means the customer runs out of hot water mid morning!!

Not wiring the middle element to the off peak, its already connected to the standard rate. They have no off peak tariff at the moment anyway.

In any case, she doesn't have a bath, just an electric shower. So she'll survive in the meantime without bottom element, which she hasn't tried to use since moving in. Once they get their off peak tariff sorted, they'll decide what to do with the faulty bottom element. :)
 
Being as its Friday, I thought I would continue this thread with some debate.

I intend to fit some form of simple timer for this old ladies standard rate 3kw immersion. I'm thinking of fitting one of these;
View attachment 35404
The manufacturer states its switch rating is 13amp resistive (3kW), and specifically immersion heaters. I've sighted this particular example, because she can also isolate (for her piece of mind) the immersion. However, as you can see it also has a BS1362 13amp fuse.

Now I was always under the impression, that 13amp FCU's should not be used with 3kW immersion heaters, but 20amp DP switch instead.

With a 3kW load and nominal 230v, would give a current of just over 13amp. Given the site voltage will be higher, the Ib would be less. I cite this debate as one such example of not using 13amp FCU;
IET Forums - Fused Connection Units to 3kW Immersion - http://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=61551&STARTPAGE=1&FTVAR_FORUMVIEWTMP=Linear

The manufacturer and others offer these products for use with immersion heaters, yet the debates over the years suggest not to use 13amp FCU's, or is that just an urban myth :)
 
13amp FCU's have been used for decades, myth.?Yes it was many years ago, when worked on a contract for a council borough changing IH, they insist on it.Just to add IMO no point putting it on a timer yet, if it is still on standard rate, same price 24hr.
 

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