Installing timer on immersion heater

jwalton4

jwalton4

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Hi all,

I have a Heatrae Sadia Megaflo water heater. The heater has two immersion elements, both of which have been wired to separate 20A control switches.

Unfortunately, the heater is not programmable and has no timer settings. I do not use the booster heater. The primary heater I manually switch on and off at the wall, as and when. Of course this setup is inconvenient and so I'd like to install a timer.

My current plan is to install a timer switch like this one. However, I first wanted to check that my current plan is sensible. I have little experience and knowledge with electrics, having only changed a few plugs and wired a couple of switches in my time (I'm eager to learn, so open for general reading recommendations). As such, I was hoping for feedback that i'm not doing anything silly.

Thanks for your time
 
I am under the impression the megaflo is very well insulated. This means that even if not switched off, once hot it does not use power, and unless water is drawn it is auto off.

A timer which turns on the heater before you return to a house at weekend and off as you return to work Monday may be worth while. But used daily the saving would be very small, and could result in running out of hot water.
 
Thanks for taking time to give me feedback, it's really appreciated!

EFLImpudence, it does seem odd there was not a timer fitted. However, as ericmark pointed out, I think the intention is that the heater is so well insulated that a timer is not really necessary (I shall be testing this hypothesis over the coming months). Regardless, a timer will certainly be useful when i'm away visiting family for the weekend!
 
jwalton4 said:
Heatrae Sadia Megaflo water heater.
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What excellent diagrams that document has

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ericmark said:
I am under the impression the megaflo is very well insulated. This means that even if not switched off, once hot it does not use power, and unless water is drawn it is auto off. A timer which turns on the heater before you return to a house at weekend and off as you return to work Monday may be worth while. But used daily the saving would be very small, and could result in running out of hot water.
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It certainly looks as if it is pretty well insulated. A 145 litre version is 552 mm diameter and 125 mm high (including insulation etc.). A bit of arithmetic indicates that that implies that there is about 69 mm of insulation around it. In contrast, my standard 140 litre HW cylinders are 450 mm diameter and 1050 mm high (including insulation), which seems to equate to an insulation thickness of about 16 mm - so the Megaflow's insulation seems to be more than 4 times thicker than that on my cylinder.

Having said that, I suspect that there are probably still significant losses from the Megaflow. In order to roughly halve the losses from my cylinder over a 17-hour period (the 'unheated' E7 peak-rate period), I had to add 500-600 mm of fibreglass insulation around the cylinder (it is roughly in the middle, vertically and horizontally, of a cupboard about 5x5 feet and 8 feet tall - and I stuffed the entire cupboard with several rolls of fibreglass insulation). Having done that, in mid-winter (it's not in a very heated part of the house), with 'normal usage' that reduced the nocturnal top-up from around 7-8 kWh to about half of that figure - a saving (with off-peak E7) of around £100 per year.

Kind Regards, John
 
Some of the accompanying figures and tables of the manual are a bona fide scandal!

Thanks for your input John. I'm really intrigued as to whether adding a timer will save much energy. I plan to do a full costing, which should give an idea of how good that 69mm of insulation actually is.
 
jwalton4 said:
Thanks for your input John. I'm really intrigued as to whether adding a timer will save much energy. I plan to do a full costing, which should give an idea of how good that 69mm of insulation actually is.
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You're welcome. Despite some of the (I think flawed) arguments one sometimes see being put forward, it's hard to see how a timer could do any 'harm' (in terms of energy usage). Of course, as has been said, the risk is that it could result in your running out of hot water (or, at least, its temp falling to an unacceptable level) if it deprived (by the timeswitch) of electricity for 'too long' (or at the 'wrong' times').

For what it's worth, with my 'super-insulated' DHW cylinder, if it starts full of 'cold' water, it takes something like 8-11 kWh (3-4 hours of a 3kW immersion) to heat it up to temperature but if I use little/none of that hot water, it needs only about 1.5-2.0 kWh (half an hour or so at 3kW) to top up its heat 17 hours after the end of the previous 'cheap rate' E7 period ... but that's with about 600 mm of insulation (of sorts), rather than 69 mm.

Kind Regards, John
 
EFLImpudence said:
About the same as using the switch I would think.
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Not everyone is necessarily 'up and about' at 1:30am, which is when I would have to switch on my water heating for E7 cheap rate (and then be up again at 08:30 to switch it off). Not quite so bad in the winter, when we're on GMT :)

Kind Regards, John
 
EFLImpudence said:
Yeah, but; no, but -
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I don't think we know whether the OP has E7 (or somesuch) but, if he does, then the "as and when" of the OP's current switching might well not correspond with E7 timings, in which case a time switch might save cost (but not 'energy' - which admittedly is what he asked about).

At this time of year, if I switched on my immersion before midnight, most or all of the water heating would be done using 'peak rate' electricity.

Kind Regards, John
 
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