Shower setup

[JustMe]

Hi,

I'm about to check out tiles for the bathroom, so want to sort the shower & plumbing first.

Currently I have an electric shower which takes a cold feed and heats as the water passes through. It's a bit on the slow and drizzly side, so I want to know what my options are for POWER.

I have a combi boiler which drives most of my hot water needs and there's no header tank currently installed anywhere.

AIUI I can run a mixer tap+shower direct from hot and cold water supplies which, given the pressure from the tap at the moment, should be an improvement on the electric. But if I want real power, then a pump is required. This is where I get confused:

From what I've read, a pump cannot have hot water fed directly from a combi boiler. It seems I have two options:

1) Header tank above the bathroom, fed in to pump and on to shower - seems to be the superior solution, but I don't quite understand how this works. Is there an immersion in the header tank or does the tank fill up with hot water from the combi which then provides a reservoir for the pump and shower? In which case, where does a mix of cold water come in for temperature control? Or does the header tank store cold water which is heated somewhere further down the line?

2) Combined electric shower/pump - cold water feed, wall mount unit combines heater and pump - simpler but not as powerful/hard/fast?

Do I have any other options?

Many thanks!

[Owain]

Yes. If you have a 10kW shower and a 30kW combi then you should get about three times the *flow*. (The pressure will still be the same.)

Correct, for a pump to work you need a source of *stored* and

*unpressurised* hot water.

No and no.

Yes, you would need a hot water cylinder (which can be heated off the radiator circuit of the combi, if you want it to be).

No improvement, as the limiting factor is the 10kW available to any electrically heated shower.

Owain

[The Natural Philosopher]

Is that correxct? as long as you have

(a) adequate mains pressure (b) large enough pipework

You will get a decenbt shower flow,.

If you have

(c) a large enough combi, it will even be warmish..;-)

Yes. Scrap the combi and put in a mains pressure DHW system. If mains pressure is good enough, that will do what you want.

OR shove a cold water pump in the incoming mains to any system that DOESN't use a header, to improve flow rates

[JustMe]

Thanks for your advice. I have a few follow up questions/clarifications...

To get the best performance from my new shower, you suggest I buy pump+hot water cylinder alongside my new shower head and mixer taps?

The hot water cylinder can be heated off the radiator circuit. Does that mean use the same hot water as flows through the central heating - so I'd be showering in the water that might've passed through all the radiators? Or does that work differently?

I've had a Google, and these look a lot like the big immersion heaters I've seen - presumably these can also be heated with dedicated electric immersion, too? These seem somewhat bulky just for my personal shower use (single occupancy household) - or am I misunderstanding?

The path would presumably be: Cold water supply -> Hot Water Cylinder ->

Pump -> Shower head.

I assume that the cylinder itself can be located anywhere near to the shower - can that be above/below/same level, or does it need to be somewhere specific?

I'm not going to be doing the advanced stuff myself, but will be helping - I just need to state what I want, up front.

Cheers.

[JustMe]

I looked this up on Google. I'm not happy replacing my combi and spending cash (plus getting builders installing bulky stuff and new pipes) to replace what otherwise works fine for me - which is what this appears to entail. It's *just* my shower that I'm looking to supercharge.

I don't need to improve flow rate for running cold taps, hot taps at sink etc, as these are quite good. I just want a high-quality power shower solution.

Cheers.

[Owain]

Yes, but the energy requirement of a shower is the product of volume of water * temperature rise.

If you want *lots* of *hot* water you have to put in lots of energy.

The amount of energy off a domestic electric shower is limited to 10kW. The amount of energy off a combi boiler is limited firstly by the boiler, but as even small combis are usually 30kW + that's a significant improvement on an electric shower, and then by the gas supply to your house. If you want a really big combi you might have to upgrade to a commercial gas supply.

A good combi on a domestic gas supply will provide a standard shower acceptable to most people. However, if you want full-body jets and that sort of thing, you need more energy input than a combi can provide instantaneously.

So, if you want more hot water than your available source of energy can provide instantaneously, you have to heat the water in advance over a period of time and then store it. This is why a 3kW immersion heater on a cylinder can give a better shower than a combi boiler of 10x the power

- although obviously only until the stored water runs out, then it's a wait of maybe several hours for the store to heat up again.

Owain

[Owain]

No; I suggest that you run the shower off the combi hot water and see how that goes. That should be a fairly minor plumbing job as you only have to run a hot pipe from the combi to the shower location. (I assume that mains cold is already available for the existing electric shower, washbasin etc. You may be able to take the hot from the existing washbasin etc rather than going all the way back to the combi.)

The limiting factor of such an installation is (a) the flow available from the mains, (b) the output of the combi. I think the Boiler Choice FAQ [1] has details of how to measure your mains flow to determine whether it is likely to be adequate.

If you then think you need more oomph you will have to look at some form of stored and pumped hot water system. If you have inadequate flow available from the mains, you will need stored and pumped anyway.

Ordinary boilers have a closed circuit running through the boiler to the radiators and a coil (heat exchanger) in the hot water cylinder. The water in the closed circuit is heated in the boiler, and the heat transfers to the water in the cylinder by means of the coil. The water in the cylinder (that comes out of the taps) doesn't go through the boiler.

Various means of valves, timers and thermostats control whether the hot water in the closed circuit is circulated through the radiators (for heating), through the cylinder coil (for hot water), or both, as required.

The combi boiler is exactly the same as far as the radiators are concerned; it just has the additional function of instantaneous hot water. You can add additional 'zones' to the radiator circuit to heat different sets of radiators at different times, or add a hot water cylinder to the circuit.

No, that's them.

Yes.

The cylinder can be anywhere, but the cold water header tank (which you would also require) has to be higher than the shower. There are also some restrictions on where you put the pump.

Owain

[1] Courtesy of Ed Sirett: The FAQ for uk.diy is at fitting FAQ CH FAQ a Boiler FAQ Fitting Standards Docs here:

[JustMe]

I'll take your advise and run the shower direct from cold/hot water supplies fed from mains/via combi to start with - even *I* can install that! I'll just replace the bath taps with one of those all-in-one bath tap/shower hose connection things and see how I get on.

Cheers.

[JustMe]

OK, I'm getting my head round this now - thanks for explaining in a manner I can understand. I'm pretty sure that the cylinder route is one that I don't want to follow, and have taken your advise, above.

Thanks again.

[Owain]

Although this might not be such an issue if you are the sole occupant of the house, paying more for a thermostatic/pressure-balancing shower valve does increase safety and convenience by helping to avoid temperature changes when something/someone else opens a tap elsewhere.

Also separate H& C knobs can mean twiddling to get the chosen temp.

Some valves, intended for pump storage operation, don't work well on combis, as the thermostat in the valve 'fights' the the combi. Check individual models for recommendations.

Owain

[David Hansen]

On Thu, 06 Jul 2006 20:01:25 +0100 someone who may be Owain wrote this:-

Part of the skill of designing a stored hot water system is to ensure, for some level of confidence, that the stored water does not run out. This is something of a black art, especially in places like hotels and hospitals. In a large house it may often make sense to have more than one cylinder, rather than one large one.

An extreme example of the value of stored hot water systems are showers for use in case of nuclear contamination. One wants a great deal of hot water suddenly and a plant to create that amount of hot water instantly would be very large and very expensive. It is far better to store the hot water ready for the off, accepting the standing losses.

Though that does depend on the heating strategy. For daytime use the immersion heater should get the top part of a cylinder up to temperature in 30-45 minutes. If it doesn't then more cylinders or more heaters may be desirable.