Electric heating..

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presta

Guru
I've lived most of my life in a house with hot water on demand, how good it is depends on how it's done.

1. Gas multipoint. This, in principle, is like a combi but without the heating, just hot water. The house was built with one of these, so we kept it and had a separate boiler when we got central heating.
2. Combi. I replaced both multipoint & boiler with one of these 5 years ago.
3. Electric. For tap water I've only used the ones typically found by the basin in toilets, but I have an electric shower.

The multipoint was a mechanical one, they're probably electronically controlled by now, but you had to get used to varying the flow to adjust the heat. Mine was ~22kW IIRC, which was ok, but a bit skimpy in winter, anything under 20kW is a non-starter IMO. It warmed up quite quickly, and wasn't a problem in this respect.

When I got the combi I wasn't at all fazed by the prospect of having to run the tap whilst the water heats up, having been used to it, but I misunderstood the critical difference between combis and multipoints, and the combi takes a lot longer than the M/P did. The old M/P had a heat exchanger made from thin copper sheet which has tapwater heated directly by the burner, and it has little thermal inertia. By comparison, the combi has two heat exchangers: one from flame to heating water, then a secondary one from heating water to tap water, and this, combined with the fact that it's a bulky casting makes it much slower to warm up. In addition, the warmup time is unpredictable, depending on whether the roomstat has the heating on or off at the time you run the tap. It does have a mode in which it keeps the water hot on standby, but I've never used it, so I don't know how well that works, perhaps I ought to try it. The energy waste may well be minimal given that most of it will find its way into the kitchen anyway.

The upside to the combi is that it's much more powerful (28kW), and elctronically controlled, so there's no faffing with the flow rate to get the temperature you want, even in winter. It will also run a shower, my multipoint wouldn't (but new ones may, I don't know), because I still have the electric shower that I had before the combi.

The first one was 6kW, and that was hopeless, you struggle with inadequate flow and luke warm water in winter, my current one is 10.8kW, which is fine for me, but it won't compete with a power shower. With electric showers, one thing to understand when you get to buying a replacement rose is that it's vital that it matches the power of the shower. If you have one that has too many holes, or the holes are too large, in winter you will be faced with choosing between a fast flow that's too cold, or a slow flow which is warm enough but pours instead of spraying. If you have a rose with too few/small holes, the converse is true: in warm weather you may not be able to run it fast enough to get the temperature below scalding.

For electric tap water, I think you'd need at least 20kW, as I said above.

Horses for courses really, I've never known what it's like to have to wait for a tank to warm up, or run out of hot water. Another difference is that without a tank you've got no airing cupboard.
 
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