New Shower/Pump

[DSA]

Hi,

We are starting to think about renovating our bathroom, and intend to add a shower over the bath. We are currently looking at a Mira Excel (Exposed valve - as I imagine that these are much easier for the plumber to fit in an existing property!) as these appear to be fairly universally accepted as the best. The heating system is conventional, with 2 tanks in the loft. The boiler has been recently replaced (Baxi conventional condensing type). Cold water to the bathroom is currently mains fed. I understand that the shower needs to be fed from the cold water tank, but presumably the bath/taps can remain mains fed??

I would guess that the distance from the shower head to cold water tank is about 1-1.5m max vertically. Do you think this shower should be pumped to achieve a good quality shower?

If so, I wonder where the pump could be sited. I read that it should ideally be on the floor adjacent to the hot water cylinder. There is not adequate room in the bottom of the airing cupboard for this, so could it be sited 'under' (or more precisely in a void at the end of) the bath?? What sort of pump would we require, and roughly what cost would this be? For example, is the cheap one at Screwfix OK or should we look at getting the Mira one??

Finally, how are pumps normally wired in? There is a dedicated 16A circuit into the airing cupboard (also sited in the bathroom) for an immersion heater - is it acceptable to use that circuit as a radial, or do I need to factor in the cost of a new circuit? (not a major problem as the consumer unit is only in the adjacent room).

Many thanks.

 

[DSA]

Has no-one got any thoughts on this? I hoped it would be relatively straightforward, and I need to move this forward!

 

[samba12]

Yeah you can put it under the end of the bath, 1-1.5m head doesnt sound much

I recommend Stuart monsoon twin (pumps hot and cold from tank, they are very good quality brass pumps, quite dear though, 250 quid, but will last 10-20 years

If you put the cold to the shower on the mains then you use a single pump, just for the hot, but only if mira excel is a thermostatic mixer

Can plumb it in with flexible hoses,

It can be wired in with a 13A fused switch or with a normal plug

 

[electronicsuk]

The wiring regs do recommend that any fixed loads greater than 2kW (I.e. immersion heaters) are fed from their own dedicated circuit. Putting anything else on the existing circuit would be in contradiction to that, but it's still just a recommendation. What you propose would be unlikely to overload the circuit and should work fine, but without seeing the job in hand, nobody can say for sure.

However, it would make sense for the pump to be RCD protected, and unless your consumer unit was installed in the last couple of years, it's unlikely that the immersion circuit will be.

The best way to power the pump, IMO, would be via and fused spur fed from the ring final (ring main) and mounted outside the bathroom. If the existing final circuit isn't RCD potected, use an RCD FCU. Also, the bath panel must be secured by means of screws or a similar fixing method that requires use of a tool to remove. Otherwise, the area under the bath will be classed as zone 0 and you will not be permitted to put the pump there.

As it's a bathroom, all this work comes under part P of the building regs.

 

[DSA]

Thanks, I guess it may be time to get someone in to take a look at the job, especially with regards finding room for the pump which you seem to recommend as being a good idea. A FCU off the ring final would not be much of a problem - can be taken from socket in the loft. House rewired about 5 years ago, so rings etc. are on a 30mA RCD - lighting/immersion etc. on 100mA RCD (TT System with earth rod). We'd need an electrician anyway because the light needs changing/probably an extractor fitted/?bonding adjusted, or at least refitted to new pipework. Hopefully that would all be possible to do in a single day.

Could the pump be wall mounted above the hot water cylinder, or will this be too high??

 

[seco services]

you put the mixer on uneven pressure you'll be asking for trouble.

 

[BigMack]

I agree with Seco - there's no point buying an expensive mixer if you're going to run uneven pressure through it - plus it will shut off all the time if anyone uses a tap whilst the shower is on.

As for pumps I always go for Salamander, I think they offer the best performance/value of any brand but Stuart are excellent too. If you're just running one shower then an RSP 50 should do the job nicely - (http://www.plumbersdepot.co.uk/products/salamander-shower-pumps-rsp-50-twin/79/?cid=) that's the best price I can find and I've used plumbersdepot a few times and they've always been good.

You can install the pump directly above the hot water tank but if possible I'd put it on the floor/ under the end of the bath. You only need floorspace equivalent to the size of a shoe box. As for wiring it up - it takes less than 2 amps so you should be able to put it on the immersion heater circuit but a spur off the main ring would be ideal. Remember that you’ll need an essex (or surrey) flange on the hot water supply to prevent pushing air through the pump. You’ll probably need to put a new cws tank in the loft (min 80 gallon) to feed the shower and run 22mm pipework to ensure best possible flow rate.

 

[DSA]

A RSP50 as opposed to a CT50+? The only difference I can see is the CT50+ does 10-20 l/min flow rate, and the RSP50 does 20-40 l/min flow rate. There will only be the one shower in the property. How can I work out the minimum/maximum flow rate that will be required for the excel shower? Do I need to examine the graphs on page 9 of the shower instructions? Link to Instructions

In addition, the Mira installation instructions are very clear that the only allowed hot water connection is via a 90deg tee off a 45deg cylinder/vent pipe, to minimise air separation. They also state that the pump must be sited at floor level.

In terms of sizing the cold water tank - will the bath/bathroom taps also be fed from it, or can they remain at mains pressure??

P.S. The RSP50 pump was £115.20 in Screwfix Catalogue 98 (is now £159.99). It will no doubt appear at that price again in the not too distant future... The CT50+ was £89.99 and is now back up to £119.99.

 

[DSA]

I've just had a quick measure up, and the existing cold water tank in the loft measures roughly 18" x 24" on plan at the top (tapers slightly up the height), and 18" tall. I'm not quite sure what this would equate to in gallons.

From the sounds of it, we would be best to increase the size of this tank? N.B. Just the one bathroom in the house, but we only want to do all this once - hopefully then will be good for 20ish years!

The other problem is that the distance from the top shower head position to the bathroom ceiling is only about 600mm. Therefore the tank may need to be raised up slightly to achieve the min head requirement.

As an alternative I did just wonder about changing the system from vented to unvented. Is this even possible (Baxi Solo Conventional boiler - about 2 years old), and would it be expensive?? This would remove the need for the new tank and pump.

 

[BigMack]

A RSP50 as opposed to a CT50+? The only difference I can see is the CT50+ does 10-20 l/min flow rate, and the RSP50 does 20-40 l/min flow rate.

I would recommend the RSP over the CT - despite having the same pressure rating the pumps are based on very different designs, the RSP has a large motor that operates virtually silently whereas the CT has a much smaller motor that emits a loud mechanical whine when in operation. The extra flowrate of the RSP50 will make a big difference as well.

You can continue to feed the bath/sink taps off the main. An alternative to the 90deg tee off a 45 degree vent that Mira suggest would be a surrey or essex flange.

As regards the cold water tank, based on your dimensions I estimate that it's around 23 gallons so it will need to be replaced or a seperate tank to feed just the shower will need to be installed. 600mm head from the shower to the tank is adequate - raising the tank is a bonus but not essential.

I don't have much experience of shower pressure on unvented systems so someone else would be better able to advise you on this but my limited experience suggests that you won't get the same results re: shower pressure as a pumped vented system.