Pumped shower - use 22mm bath feeds?


Postby stephensont » Mon Jan 18, 2010 1:26 pm

Hi,
We're in the process of converting a bathroom into a shower room, and want to replace the existing bath with a walk-in shower. Along with this, we ideally want to install a "proper" thermostatic shower (probably with a pump) rather than an electric shower.

Having spent some time scouring the forum for information it seems that to get a decent flow rate to the shower all pipework feeding the pump must be 22mm... hence this question:

Now that we've removed the bath I've been able to determine that the feeds to the taps are both 22mm runs - one from the cwt in the loft and the other from the hot cylinder. The basin & WC supplies were then teed off these feeds via 22m to 15m conversion fittings and 15mm pipe.

Rather than installing new dedicated feeds & another take-off from the cylinder, can anyone see a problem with using the original feeds to feed a shower? The shower room would effectively be single use so the feeds would to all intents & purposes be dedicated to the shower while it was being used... the WC won't be used at the same time as the shower for example!

We've got good cold pressure thanks to the loft cwt but the hot's not as good - hence expecting to need a twin-end pump. Assuming this is the case, there's nowhere in the bathroom to fit the pump (and if using the existing feeds don't really want to fit it in the airing cupboard) so we're considering installing it in the loft.

If we fit a negative-head pump (on the basis that it will be located above the hot water cylinder and on much the same level as the cwt), would there be any issues with taking the 22mm feed through 90 degrees to run it up the wall to the loft, into the pump, with the pump outputs running back down the wall to the shower mixer (presumably also in 22mm)?

Thanks in advance for any comments or assistance!

Tim
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Postby chris_on_tour2002 » Tue Jan 19, 2010 8:37 pm

you will need to run a dedicated supply for both hot and cold to maintain equal pressure on both sides of the pump. if, for example, somebody were to flush the toilet whilst somebody is in the shower then the pressure will drop on the cold side - potential risk of scalding.
even modern thermostatic showers can run very hot if only for a brief moment.

also the feed for the bath hot most likely comes from the feed at the top of the cylinder thus on the same circuit as the vent pipe. ergo risk of sucking in air, potentially burning out the pump and causing airlocks.

not the news you wanted but best to do it properly.
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Postby stephensont » Wed Jan 20, 2010 8:42 am

[quote="chris_on_tour2002"]you will need to run a dedicated supply for both hot and cold to maintain equal pressure on both sides of the pump. if, for example, somebody were to flush the toilet whilst somebody is in the shower then the pressure will drop on the cold side - potential risk of scalding.
even modern thermostatic showers can run very hot if only for a brief moment.

also the feed for the bath hot most likely comes from the feed at the top of the cylinder thus on the same circuit as the vent pipe. ergo risk of sucking in air, potentially burning out the pump and causing airlocks.

not the news you wanted but best to do it properly.[/quote]

Thanks for this Chris. Definitely want to do this properly so guess my next task is to fully trace the pipework back from the bathroom to the source to check what else is or isn't attached.

Getting a dedicated cold feed isn't a problem as I can run a new feed & take off from the loft CWT. Assuming the cold is dedicated, and the hot is supplying nothing else and not connected to the vent pipe, presumably I can reuse it for a pump?

While tracing the pipes I'll also try and make some room in the airing cupboard for the pump....

Any thoughts on whether I'd need to run 22mm pipes from the pump to the shower too, or would 15mm generally be Ok? Bathroom's only 3-4m from the airing cupboard and if running 15mm I can probably install the pumped shower pipes under the floor rather than going up into the loft, across, and back down....!

Thanks for your help,
Tim
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Joined: Sun Jan 03, 2010 8:26 pm


Postby chris_on_tour2002 » Wed Jan 20, 2010 5:34 pm

unlikely that the bath is being fed from unvented pipe to be honest. even if it is i'd have my reservations about running a pump from it as the bath and basin taps are potential points for air ingress if the seals aren't tip-top. also means that the bath/basin hot taps cannot be used whilst the shower is running - and if the taps are opened whilst the pump is running air is likely to get sucked in if the pump pulls water away from the taps - physics will always follow the line of least resistance and as air is less dense than water...

with regard to 15/22mm pipe, if the pump has connections intended for 22mm i personally would run 22mm for as far as possible, reducing down to 15mm as close as poss to the shower. this is for two reasons; 1) to give the best possible flow rate to the shower and 2) the 15mm bore of pipe will increase resistance to the flow, therefore put greater strain on the pump which will affect the reliability/longevity.

hope this helps.

chris
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