Showers 9.5 vs 10.8Kw

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Can anyone tell me whether there is any significant benefit between the Mira 9.5 and 10.5Kw electric showers. I have used the 9.5 in the past and it was, well, disappointing. I have the catalogue in front of me but it does not detail flow rates between the two. It also states that the 10.5 can be wired on 6mm cable. Is that right or will I have a new heating element in my loft? The cable run is 25 metres.
Thanks.
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It's only (elementary) physics. Water takes a boatload of energy to heat up. Wattage is power, which is energy-per-unit-of-time. So, upping the wattage by 10% from 9.5 to 10.5 will up the energy available by the same factor, i.e. not much. If you were getting, say, 7 litres per minute the old shower, you'll get 7.7 with the fatter one. Yawns all round. (This assumes that both are equally efficient, which for electric showers is a fair assumption, with really close to all the energy going into heating the water - it doesn't have much place else to go!). So don't expect a huge deluge where you had a trickle before. (It's possible your previous showerhead was scaled up, and a thermostatically-controlled shower won't let more water through than can carry away the heat generated at the selected temperature (if you follow my on-the-fly syntax ;-), so a new shower *might* be significantly better than what you've got used to. But it's not likely, and could've been achieved by putting in a new showerhead rather than a whole unit).

Like it says above, you won't get more than a 10% uplift.

25m is straining at (or beyond) the limits 6mm cable with a 10.5kW load, on grounds both of voltage drop (which will eat up some more of the heating you want!) and of earth loop impedance (you want shorts to make the fuse blow/breaker pop, *fast*). I'd err on the 10mmsq side; but by all means go over to the on-line cable-sizing resources to check. You know it also depends on the cable routing, don't you (the harder it is for the cable to dissipate heat cos of thermal insulation, no-free-air, etc., the less heat you can let it generate)...
HTH - Stefek
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Electric showers are always disappointing, unless you are a hamster.
A small combi boiler is around 24kW. A large one is around 35kW. A heat bank is around 100kW. A hot water cylinder is limited only by your water flow rate. Say 200kW if you have good mains flow and an unvented cylinder, or a vented cylinder and a decent pump.
I think you might agree that 10kW doesn't really cut it. 24kW runs a good standard shower, but not spectacular in winter if you like them hot. You'll need at least 35kW and more like 50kW to run a multijet panel shower.
According to the TLC cable calculator, a 10.5kW shower at 240V (which is your likely actual supply voltage for this power rating, rather than the nominal 230V) requires 10mm cable and a 45A MCB. Voltage drop will be 2%, dropping the developed power to 10.1kW.
Do you not have a hot water system available? These can almost always be made satisfactory for shower use.
Christian.
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They work very well in winter, unless you are into drencher showers. The performance of any high pressure shower can be improved by using an aerating or atomising shower head.

Yes by installing a 250 Stuart Turner power shower pump plus fittings. Anything less is a waste of time and eventually money. If a regular boiler is in place, for less than 400, depending where you go, maybe a lot less, a combi can be installed in its place. This will just perform the duties of the old boiler in:
- heating the DHW and CH - the added benefit of giving power shower performance - a shower that never runs out of hot water - never having to wait for the cylinder to reheat - no vibrating power shower pump waking up the house at 6.00 a.m. - doesn't take up space in the airing cupboard as the pump will - a newer more efficient boiler - etc
For little over the Stuart Turner pump a straight swap for a combi can add so much more value.
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But a pump is very simple to install. A combi boiler would cost a fortune to install, especially as most people would not be confident to do such a major upgrade.
Also, you are comparing the cheapest combi with the most expensive pump. I spent 100 quid on a single impeller pump to improve the hot supply and it ran for years with no trouble. I've sold the house now and it was still working then.
Christian.
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Is it not a requirement to have a water meter installed, if a shower pump is fitted, and could this add to the costs, in increased water charges?
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Gavin Gillespie
Giltbrook
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https://www.southernwater.co.uk/customer_zone/domestic/Household_metering_enquiries/default.asp
"You MUST have a meter installed if you:
use a garden sprinkler or other unattended garden watering device (this does not include handheld hoses)
and/or
have a swimming pool with a capacity of 20 cubic metres or more which is automatically replenished with water"
No requirement for having a shower pump (at least, not with Southern Water)
D
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I could not find any reference when I did a search, but I'm sure that I read it somewhere, perhaps I was dreaming. :o)
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Giltbrook
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Technically, almost any modern plumbing system could have a feature effectively requiring you to inform the water company to decide if you need a meter. No-one bothers.
In any case, the vast majority of people save money on a meter, as the 5-10% of people with hosepipe fixations use such a large proportion of the water.
Christian.
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So is a straight swap combi. Boiler in, boiler out.

This is DIY

Yes, that is so. Comparing like with like. The most expensive pump can't even compare with a combi performance. Cheaper still, if you room at the back of the airing cupboard, install a Main Medway multi-point for around 320 or so. Or if you have a well ventilated room, install an open flued single point Chaffotauex water heater supplying the shower only. 151.58 Inc VAT giving electric shower performance at 1/4 of the running cost.

Lucky and it probably woke the street first thing in the morning.
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Assuming that all the pipes are in the right place, and is suitable for their system etc. When my parent's boiler died, they had a very low selection of boilers which supported their installation (gravity etc). Maybe it was restricted by the plumber - but apparently they had very little choice due to how their system was set up.
So, maybe a complete re-plumb as well for the CH system?

Yeah, but I'm sure that most people here would not consider a new boiler to be within their DIY skills. "Suitable competent person" is ringing round my ears, and no matter how much I can read up on it - I'll never consider myself competent enough to install and commission a boiler. You may be - but I'm not.
D
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and at what point does the original poster say that he has a boiler he can swap for a combi, infact he doesn't even say if he has a CH system at all
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You're having a laugh! Almost any pump is better than a combi, especially if you are trying to run baths as well. However, both would be excellent performers for just a shower, so it is immaterial.

I would not encourage the installation of an open flued appliance anywhere, let alone in a bathroom.
Christian.
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Not so.

The suggestion was just one shower, not run the baths through it.

Got it.

No it is not. Look at the benefits for about 150 extra outlay. I highlighted them. If the boiler is an old cast iron iron even a regular combi will outperform it in efficiency. And you still get quick bath fill-ups too from the cylinder.

Still legal and millions of them are about. Can't fit one in a bathroom. You can have them in utility rooms and kitchens.
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On Tue, 28 Oct 2003 17:14:59 +0000, Christian McArdle wrote:

A flueless heater would be even more pathetic than electric shower even the 9.5kW one. Also the manufacturer is likely to forbid such a use anyway.
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Ed Sirett - Property maintainer and registered gas fitter.
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Flueless water heaters can be used for a single point shower. They can't be fitted in bathrooms.
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A pump might be cheaper than replacing the boiler, possibly by a factor of 5-10.
Christian.
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A cheap and nasty pump, maybe. One that is less noisy and far more reliable then no. I gave a ball park on figures. The combi replacement has "many" benefits for little extra cost. The way to go.
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How much do you think you can get a combi installed for? Not the purchase price, but the installation cost? Include the cost of the pipe run from the combi to the bathroom as you suggested keeping the original cylinder for other outlets.
I think installation will be well over 1000 pounds. Very few people would be willing to DIY this.
Christian.
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This is DIY. Combi? I have seen them for 360 with enough flowrate to do a shower.
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