Pumped shower. Probably a daft question....

[Nick]

My son has just bought a house in Bristol. The house is heated by a combi boiler. He would like to install a pumped shower. I have no experience of combi boilers but understand that they will supply heated water at mains pressure. There is no cold water storage tank or DHW cylinder in the house. Thus I presume a shower pump is a given no-no. Water supply at the house is not great in terms of flow or pressure. Certainly not adequate for a powerful shower. No doubt many folk have combi boilers and powerful or pumped showers. So, what are the options for arranging a good shower installation please? As said, this is probably a daft question. Perhaps I should find my old tin hat.

Many thanks, Nick.

[ARWadsworth]

Is he prepared to zone off the combi boilers CH output and add a tank and HW tank?

I know someone who did that. He also had 3 bath taps! The idea was the 2nd hot tap could use the cylinders immersion heater in the event of a boiler failure.

[jgharston]

Me! I love having a tank full of hot water on tap and 25ft of water head to the shower. :)

JGH

[YAPH]

A pump is for low pressure supplies: the combi will supply water at mains pressure which will normally be better than most shower pumps. All your son needs is a thermostatic mixer valve. Bar types are cheap and easily replaceable when they eventually pack up; alternatively Aqualisa and Mira are expensive but quicker-responding to temperature fluctuations, and have spares available when they are needed. No-name shower valves with non-standard fixings and no long-term spares availability are asking for trouble in the future.

[fred]

In article , Nick writes

Bottom line is that he cannot sook from the mains[1], it ist verboten.

If he wants a pumped shower then he must go backwards (allegedly) to stored water with header tank and pump that instead (same boiler but hot water heated off the CH loop).

[1] Via combi or otherwise

[The Natural Philosopher]

25ft? I've got nearly 5 bar!

The tank is about 150 feet high on the highest point of West suffolk..I can sometimes see it poking above the trees.

[John Rumm]

That is correct.

Three options really...

Upgrade the incoming cold main to provide adequate flow rate (its static pressure is probably ok)

Install a traditional gravity cylinder and storage tank in the loft, plus pump etc. (the combi could heat a traditional cylinder as well as running the rads and retaining its direct hot water generation capability).

Install an accumulator to buffer the main cold feed. This allows for a period of higher flow rate than that directly available from the mains.

[Andrew May]

Isn't the limitation likely to be the rate at which the combi can heat the water rather than the rate at which the water board can supply it?

[John Rumm]

For high volume water uses that is typically true... (unless the combi is unusually powerful). However for shower uses, combis will usually cope very well unless the shower is a type with a particularly high water consumption type like one of those with a 12" wide "soaker" head.

A shower that needs 10 lpm or less (the majority) should be adequate even on a fairly weedy 24kW combi.

To make a proper assessment one needs data. i.e. see how long it takes to fill a bucket of known size, and also perhaps a check with a pressure gauge of the type you can fix to a washing machine tap.

[newshound]

Not in my experience, owing to the pressure drop in the heat exchanger when on full flow.

[Hugh - Was Invisible]

Static pressure is some guide but pressure and flow are necessary. Flow (but not static pressure) may be reduced by a combi boiler and the size and configuration of the supply pipes from house entry to the shower.

Here we have plenty of pressure in the winter but it drops dramatically on summer evenings (no hose pipe ban here yet)

[The Natural Philosopher]

Indeed. Combis will throttle the flow rate so the water does in fact come out hot enough.

the only way to get SERIOUSLY high flow rates is a pressurised hot water system in areas that actually have decent mains pressure and can support a decent flow rate.

I've got both, but even here there is a weird effect when I turn the cold tap on - the water starts of with a little spurt, then builds up over a second..I suspect it takes that long to accelerate all the water in the underground main. (i've got at least 150 meters of plastic to get to the outside stopcock!)

[Adrian C]

We now have our shower with two shower roses.

One on electric at mains pressure, the other on the gas hot water tank, non pumped. The latter is a pathetic dribble and now complicated to put right with a pump, so the electric gets heavier use.

Which was not the original intention. Oh well, she 'designed' it.

:-(

[Adrian C]

Pressure washer, inlet hose siphoning water out of a hot bath?

An Option.... ;-)

[grimly4]

My bathroom-under-construction has a CWT, HWC and 3/4" piping dedicated to the shower on the ground floor, with ~ 15' of head. Preliminary results indicate it to be more than adequate, but just in case, there's an electric shower as back-up. I haven't even looked at the need for a shower pump yet, as I doubt I'll need it.