Hey everyone I have recently had a combi boiler installed (Potterton heatmax HE 28). It replaced a back boiler that was with a tank in the loft. The new boiler is situated in a bedroom cupboard on the first floor. I want to install a stand alone thermostatic shower (not chosen one yet but max £200) in the bathroom (next door to the bedroom). There is a 22 mm hot water pipe and a 15 mm cold water pipe servicing the bath and hand basin. I've read about water volume and water pressure and most shower manuals I have read specify that there has to be equal water pressure to the valve. The nearest point I can tee off the incoming pipes is about 6 feet away from the valve and the furthest point is about 12 feet away from the new shower valve. Do i tee off the 22 mm hot water pipe with a reducer at the nearest point or furthest point OR do I tee off and continue with 22 mm until just before the valve where i then reduce the pipe to 15 mm. Though I've said I have read about volume and pressure it still does my head in. Cheers
Your boiler will deliver about 12-15 ltrs/min of hot water depending on supply, cold varies depending on various elements, having a 22 hot from a combi isn't great but that's what was there when Gravity was as play, check your flow rates with a weir gauge for suitability with the min flow rates of shower, you have equal pressure unless you have a pressure reducing valve fitted somewhere between the cold to house & cold to combi
Thanks for that G&W. It's an old Victorian house that has needed a lot of renovation - most plaster has been hacked off and replastered, extra sockets added and rads moved or changed ( sometimes i wish i had never brought it). I have had a lot of the floorboards up and have not noticed any valves - where would a pressure reducing valve likely to be placed and would it be beneficial to install a pressure equalising valve
When they say equal pressure for mains fed they are referring to combi, unvented or boosted water. A combi installation is equal pressure as both hot & cold are equally balanced, eg if the pressure drops at the shower because of an opened cold kitchen tap, the pressure will drop on the cold to the shower and to boiler resulting in balanced pressure. If you have very high mains pressure then a PRV would be fitted on the incoming main after the Double check valve normally under sink. Do you have 2 or more showers?
You can't have 2 or more showers off a combi unless 1 is electric, This is due to exceeding the hot water flow rate of a combi, If you have 2 showers at 10 ltrs/min that's 20 needed, your boiler will do 15 max, result is a shower that dribbles out. Unvented will do around 26, You can fit flow restrictors to other outlets e.g basin 4 ltrs, sink 5 etc, this will allow flow rate needed for shower & minimise fluctuations, you must fit thermostatic showers, you can modify the cold main from 22mm to the split for the boiler supply too
You can have as many showers as you want from a combi. But only use one at a time... All new pipes to your new shower, run them in 15mm. I wouldn't bother with any pressure reducing/balancing valves as the chances are they won't be needed - and they can be fitted afterwards if they are. Tee-off wherever is more convenient, and use 15mm pipe. Check the specs of the thermostatic showers you are considering - make sure they are suitable for combi ('high-pressure') use, and also that the hot doesn't have to be at a certain temp for the thermostat to work properly (I fitted a nifty Victorian shower to my combi, only to read afterwards that the hot should be delivered at a minimum temp of 60oC - which it simply ain't. Needless to say, adjusting the shower temp has next to sodall effect...
Thanks DA. As you say I can fit any valves after if needed. Most manuals I've read so far are quite informative. Cheers
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