Thermostatic or electric shower from combi

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I'm about to install a new shower. I've got an 80k btu Sime combi boiler.
Can anyone recommend whether it's best to install a thermostatic shower connected to the combi boiler, or an electric shower?
Has anyone got direct comparisons - e.g. is a thermostatic shower from an 80k btu combi definitely more powerful than even a 10kw shower?
Any advice much appreciated.
Thanks
eno
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80K BTU is around 24kW. In terms of shower performance, this will be a change from approximately 4 litres per minute to 10 litres per minute.
Christian.
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Thanks for that info Christian.
Just to be clear, you compared the ( 80k btu = ) 24kw from the combi to 10kw from the electric and did the ratio to get 10lpm versus 4 lpm?
If that's the performance difference then I think there's no question which I should use. It's in a one bedroom flat, just me and my girlfriend, so even the supposed downsides of running the shower from the combi won't bother me with that performance.
The shower I'm about to replace is only an 8kw, so presumably I'll see even more benefit from using a thermostatic.
Thanks again Christian.

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I don't see any downside whatsoever from running a shower from a combi. people buy them for their power shower type of performance. A good normal power shower pump costs 200-250. You can pick up a combi for under 400, that does the heating and gets rid of tanks, liberating all that space, as well.
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IMM

Maybe I misunderstand how they work, but I'd been led to believe that if the shower is supplied from the combi, then for the time that the shower is in use, the radiators won't get supplied with water therefore cooling the rooms down? (And some showers take longer than others... ;-) )
Also, if the shower is in use, and someone does use a hot tap, the shower would be affected somehow, even if it is a good thermostatic one?
If these points are wrong, I'll gladly stand corrected, and be even more keen to get a thermostatic shower!
I suppose there's also the issue of not having a backup hot water supply (like an electric shower could give me) if the combi boiler breaks down, but that's not a big worry to me.
Thanks for your comments IMM.
Eno

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That is true. But if a house is up to temp that will not be a problem. Also there are overpowered fro CH and when they come back onto CH they warm like the wind.
It will have to be a very long shower to effect the heating temps.

You install a pressure equalizing valve. Some shower mixers have them built-in, see the Screwfix catalogue. Turning on the kitchen tap, unless it is a bottom of the flowrate range combi, will not effect the shower too much at all. Best get a combi that delivers 13 litres/min minimum. Some combi's right up to 22 litres/min.

They are wrong.

You can fit an instant electric heater in the hot outlet of the combi. If the combi is down turn it on. It only trickles, but backup it is and it will clean you. All problems solvable.
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IMM wrote:

haha. It depends on teh combi and the mains pressure. I vidly remember trying to wah my hands in a GF's downstairs toliet whuile the teenagers upstaits had showers. No way Jose.
That the point about yer 400 quid combi. You get what you pay or.

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I have a Worcester and a Mira 415 shower valve. This is NOT thermostatic - but pressure equalising (see their web site). If other taps are suddenly opened the shower pressure drops - equally on hot and cold - so no problem.
It has worked well for 12 years. Only slight snag is in the winter when I find it best to 'warn' the boiler that I need the 3 way valve moving by running a tap for about 5 seconds. This ensures that the domestic water gets priority.
Mira 415 The Mira 415 is specifically designed for those with a high pressure hot and cold water supply, or with a fully modulating combination boiler or instantaneous gas water heater (please check with your installer or call Mira Customer Service for details).
a.. Pressure balanced to maintain a constant showering temperature, even with variations in supply pressure, making the showering experience consistent and enjoyable at all times b.. Maximum temperature stop limits selection of an unsafe temperature, which can be over-ridden by the use of a discreet push button c.. Produces a powerful water flow rate - like that of a power shower - because it is designed specifically for high pressure water systems. There is no need to add a pump d.. Supplied with Mira Response power shower fittings - featuring three exciting power spray patterns: Start, Champagne and Massage
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Regards

John


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mains as the shower is, whether it cools down or not depends on whether the boiler can supply enough hot water to keep the shower and the tap going at once, probably not.

far better.

water other than what you can boil in a kettle.
FWIW I had a combi installed a year or so ago, reasonably happy but wouldn't even consider it again unless I had a decent (22mm at least) incoming water main with decent pressure/flow rate.
Rgds
Andy R
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But not an issue.

1. It will not cool down if it has a pressure equalising valve either: in the shower mixer, on the mains pipe when t eneters the property or just before the shower mixer. They are 30 and available in B&Q Warehouse. The versions that do the whole hosue are 22mm and more expensive.
2. It will not cool down if the combi is powerful enough.

See my post on this point.

Well uprate the supply. What is the problems anyway. I find that many have decent flow and pressure, but the system is not piped up correctly or pressure equalizing valves are not used.
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We've sold the house now so the prob's disappeared but running 100ft of new water pipe to the road would be enough to put me off a combi if I did the project again. We had a Baxi 105e and a 15mm incoming main with a decent flow rate for that size pipe, however, I'm not convinced you can get enough water through a 15mm pipe for a house where there is more than one person using the water at once. You can compromise and fit restrictors then have kitchen sinks that take forever to fill up if someone's having a shower or lavatory cisterns that take so long to fill you're embarrassed to let guests use the loo after you. IMHO if you're in a house that's got any more than two people living in it and you must have a combi then you need two of them (or a thermal store or something) and a 22mm or more incoming main.
Rgds
Andy R
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As a general rule are you correct, and it is wise to split the hot and cold supplies as the cold water enters the building. But I do know of some 15mm pipe systems that cope super well, but these have high pressure to start with and are not 100 metres from the water main in the road. It appears yours is near a worst case example.
I know of Worcester-Bosch HighFlow combis' that are fed from a 15mm mains pipe and the hot and cold supplies are split at the stop cock. They certainly can cope two or three taps at the same time.
The moral is assess the cold water mains supply for suitability.
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Andy

Thanks, I'm pretty much convinced to go for the shower off the combi now.
It looks from what IMM said ("You install a pressure equalizing valve.") that if my thermostatic shower unit doesn't have one of those inbuilt, I should get one separately?

LOL! Yeah, and I live in Scotland where the winters can be pretty cold. What I meant was I'd rather have the powerful shower which I'll use every day, with the risk that at some point, the boiler (and shower) will be out of service, rather than go for an electric with it's poor performance just so that I'm not scuppered for water if/when the combi goes. And besides, asking to use their shower is a good way to get to know yer neighbours!
Thanks for your advice.
Eno

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See how the system works. If you have problems install one. It ensure that both the hot and cold supplies to the shower are of equal pressure, eliminating the too hot and too cold problems when other taps draw off water. The temperature operated thermostatic mixers generally are not fast enough to adjust the outlet temp to the mixers setpoint, the equalizing valves are fast.
With a mains pressure system, it is best to balance the system. Install in-line isolators and turn down taps to suit. You do not need full firehose flow on a wash basin or kitchen tap for that matter, so turn them down. Do you need full flow on a toilet cistern, probably not at all. A little adjusting here and there on all water outlet taps can improve the shower and combi performance considerably.

If my boiler packed up, the dishwasher and washing machine would still work, so would the kettle. So what do you need for backup? A small 2.5kW electric fan heater and an in-line instant electric water heater in the combi's outlet, which is for emergencies only. Normally the water heated by the combi will just run straight through it and it would be switched off.
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IMM wrote:

For once I have to agree with you. Blimey!

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Amazing! After all this time you are learning.
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"Enoesque" wrote | I'm about to install a new shower. I've got an 80k btu Sime combi | boiler. | Can anyone recommend whether it's best to install a thermostatic | shower connected to the combi boiler, or an electric shower?
Apart from the advantages to the combi mentioned by others, heating the shower water by gas will usually be quite a lot cheaper than by peak-rate electricity.
Owain
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I agree on the price paid to heat the water - we are lucky enough to have Economy7 or whatever it's called these days, so I use the immersion overnight to heat the water for the morning shower, then use the gas to heat water during the day.
Re an earlier thread, is there an easy way to tell how big the service pipe is off the main? Do you just use the Mk 1 eyeball and say it's 22mm? If that is the case, what size service pipe (typically) are Victorian houses receiving?
Thankss...R

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1/2" lead
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What price per kW is gas and overnight economy leccy?
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