Using an electric shower and combi boiler as a team to save energy!?

[MrsCabbage]

I am getting close to the first fix of renovating my house and wanted to test out an idea I have been thinking about on the plumbing side of things.

These are the two main unchangeable factors I have already decided upon

1) I am going to have a new decent combi condensing boiler 2) I will be having 2 showers. One in the main bathroom and the other in an en suite.

So the obvious problem is that when both showers are in use at the same time one will suffer for sure.

First Solution - Replace one thermostatic shower with an electric shower. But more costly at say 3/4 times more per electric shower use.

Second Solution - Have thermostatic shower and an electric shower side by side and use whichever is dictated by if the other is in use. Kind of weird looking I imagine.

OR Supply warmed water via a mixer valve to the electric shower.

The advantage I see here is if there are no other demands on the hot water the electric shower will be supplied by warm water (set at max safe temp) so the electric show would only have to rise the temperature by a small amount. But if hot water is being used elsewhere then the electric shower will then pretty much take over heating the water..

This idea seems to worki n theory in my mind, but my knowledge of practical plumbing is limited (this will have change as I'm going have a go doing all the plumbing myself). One problem maybe is that I have assumed a method/device exists that allows you to prioritise supply of hot water to different places.

Another factor that might help me out is that I have very high mains cold water pressure (my cheap hose pipes expand to twice there width!) and something close to 50 liters a minute flow rate.

[MrsCabbage]

I am getting close to the first fix of renovating my house and wanted to test out an idea I have been thinking about on the plumbing side of things.

These are the two main unchangeable factors I have already decided upon

1) I am going to have a new decent combi condensing boiler 2) I will be having 2 showers. One in the main bathroom and the other in an en suite.

So the obvious problem is that when both showers are in use at the same time one will suffer for sure.

First Solution - Replace one thermostatic shower with an electric shower. But more costly at say 3/4 times more per electric shower use.

Second Solution - Have thermostatic shower and an electric shower side by side and use whichever is dictated by if the other is in use. Kind of weird looking I imagine.

OR Supply warmed water via a mixer valve to the electric shower.

The advantage I see here is if there are no other demands on the hot water the electric shower will be supplied by warm water (set at max safe temp) so the electric show would only have to rise the temperature by a small amount. But if hot water is being used elsewhere then the electric shower will then pretty much take over heating the water..

This idea seems to worki n theory in my mind, but my knowledge of practical plumbing is limited (this will have change as I'm going have a go doing all the plumbing myself). One problem maybe is that I have assumed a method/device exists that allows you to prioritise supply of hot water to different places.

Another factor that might help me out is that I have very high mains cold water pressure (my cheap hose pipes expand to twice there width!) and something close to 50 liters a minute flow rate.

[dom]

Given that you want 2 strong, simultaneous, non-electric showers, what are your reasons for not having a thermal store?

[Grunff]

Beat me to it.

[MrsCabbage]

Ah well I have converted the Attic - and am loath to loose any space for a hot water tank (which I assume is the thermal store?).

Also, as I am going to do the plumbing a Combi boiler seems like less plumbing for me to get my head around.

And finally, from phoning around a load of estate agents I asked them as to which type boiler system was thought of as better by your typical house buyer and they said without fail combis.

But regardless of the above I would agree in a perfect world I would go for the system you suggest. But working within my remit, what do you think?

[meow2222]

thats estate agents for you :) Combis are really better avoided on the whole, unless you get a really high power one.

Another way to stretch your hot water further is to use a drain heat exchanger. The warm water going down the shower drain prewarms the cold feed to the shower, resulting in less hot water requirement

Another way to stretch it again is to put the cold feed to the hot supply through a heat exchanger, with the other side on the CH system. In winter this will give a significant extra quantity of hot water. In summer it will make that incoming water a bit less cold, but thats all. In summer people have cooler showers, so it fits quite well.

NT

[David Hansen]

On 25 Nov 2006 05:12:06 -0800 someone who may be "MrsCabbage" wrote this:-

up with many links.

A thermal store will take some space, but it will provide a far better hot water system. It isn't just when both showers are in use that one will suffer, the same will happen when a tap is opened. If there is a combination boiler that is powerful enough to avoid this it will be large, so to some extent the difference is where the space is taken up, rather than the amount of space taken up.

Not a lot less plumbing.

A combination boiler is a single point of failure. It is usually the hot water side that goes and one is then stuck until it is fixed.

[Doctor Drivel]

Space is valuable to you (why clutter valuable real estate with tanks and cylinders?). A two simultaneous high pressure showers. A high flow combi. Alpha CD50, or look at a Rinnai high flow multi-point water heater - it will give two high pressure showers, get rid of the cylinder and tanks too. The business.

Snip from a recent post of mine:

I know he detested the tank in the loft as it got in the way. He also didn't like the cylinder taking up space too. His house is a three floor town house with garage on the ground floor, heated by forced air which they love. One bathroom two showers. I suggested they spend some extra and go for a high water flow Rinnai multi-point in the loft on the gable end. Rinnai and Andrews have models which can be fitted "outside" too, saving lots of space in the house. They said yes, seeing the benefits of space saved and long showers. They get annoyed when the cylinder runs out of hot water when showering which happened far too often for them, and in the mornings too as the immersion does not recover fast enough when consecutive showers are taken.

I fitted the Rinnai last week with a flow switch in the cold supply, and the room stat of the forced air heater run through the switch, so when DHW is called by the Rinnai the air unit is switched out as the gas meter is not big enough. The air unit is a conventional flue job, with a simple gas multifunction control. The whole job took less than a day to do.

What happy bunnies. They rave over the mains pressure showers and the space they have gained. Two showers can be had whereas before they could not have two together only one with big gaps between. Now they have showers for as long as they want and when they want. The bath fills up as fast as before too.

They like the idea that the DHW temperature can be controlled by a waterproof remote temperature controller. They never went for it, but is can be easily fitted after. So you can lay in the bath and control the temperature of running hot tap. The Rinnai can have up to four of these.

Rinnai and Andrews high flow multi-points are very cost effective. And now are cheaper than fitting unvented cylinders.

[Doctor Drivel]

Ed Sirret said something recently abouit this.

See my post re: Rinnai. Appears the best way to go for you.

[John Stumbles]

An electric shower will be so poxy compared to a thermostatic one fed off a combi no-one will want to use it.

Even the thermostatic mixer shower contending with another off the ciombi is still likely to beat the leccy one hands down:-)

I don't think electric showers modulate the electric power consumption so feeding it hot water may result in excessiveoutput temperatures and safety thermal trips operating in the shower. Dunno ...

If you really don't want to mess with themal stores etc you could get a combi with a bit of storage built in, which would tide you over brief periodsof contention for hot water.

WRT to thermal stores remember they don't have to go in the attic.

[meow2222]

just not using both showers at once is so much simpler :)

NT

[MrsCabbage]

Gosh! I switch web pages and look at the how many posts have appeared! Thanks.

My my it appears the electric shower is well hated and I must agree the temporary 10.5kw shower I set up over a bath (in my temporary accomadation) only runs at 3.5 litres at a proper temperature at the moment.

I suppose I thought if I supplied hot water to it as it would barely have to heat it then it would have very little effect on the flow rate from the combi so wouldn't suffer from crappy electric shower syndrom...plus be cheaper to run.

I see your point on confusing the temperature sensor and that might vary between showers. I think it might be easier if I just try it and see.

Or has anyone else actually tried this in practice?

[John Stumbles]

If you want to try a practical experiment to see how 2 showers driven by a combi might work in practice you could get 2 shower heads of a type you might want to use for a decent shower, connect them up via some pushfit valves and bits & bobs and find a friend with a regular combi and take it round there to try out (maybe hook up to washing machine H & C outlets).

H -------+------------- | | (X) (X) valve | | +--< +--< shower | | (X) (X) valve | | C -------+-------------

[Dave Plowman (News)]

So you get rid of the cylinder and tank by fitting a combi *then* fit an additional boiler? Efficient use of space and money isn't one of your strong points, is it?

[Definitely snipped now]

No matter how often you post this story it remains that.

[Doctor Drivel]

Will you please eff off as you are a total plantpot.

[Doctor Drivel]

Just look at my posts.

[Doctor Drivel]

A silly ting to do. It has been established he needs a high flow combi or multi-point. I gave some models.

[MrsCabbage]

Yup John, I think a practical experiment is called for here. Thanks for the plan and cute little diagram!

I am lucky as I have to fit a temporary combi boiler in my tempoary accomadation, as boiler failed last week and it is cooooold here.

I will then be able to mess about with push fit fittings and 2 thermo showers and an electric shower to see exactly how my odd idea would work in practice.

I will post the results of my experiments and then conjecture will melt into fact :)

Thanks everyone for you input.

[James Salisbury]

Sounds like you could do with a pressure regulator on your cold mains supply. 50l a min is a little excessive.....

Also a thermal store could fit where the old hot water cylinder was, and no tanks required in the loft....

[John Stumbles]

So you prefer theory over practice?