Hi. I'm refurbishing an Edwardian terrace and would like a little advice from you lovely people on my plumbing scenario please. I have found some info by searching but not a definitive answer as yet. I have a kitchen (with combi boiler) and two bathrooms to plumb CW supplies from scratch. The bathrooms occupy the same footprint on the first floor as the kitchen below. The rising main under the stairs is lead - approx 22mm external diameter. This goes to 15mm copper before and after stop cock. I did a flow test off the 15mm rising main at first floor level and it is 16 litres per min. I have no plans to replace the lead supply pipe. I'm not moving into the property and I have a huge list of stuff to do without adding more to it if possible! My two big questions are: 1) Given that the inner bore of that lead supply pipe is probably no bigger than the 15mm copper it's attached to, is it pointless using 22mm anywhere in plan below? Can I just use 15mm throughout? 2) Does my plumbing plan below sound ok, given my theory on prioritising the supplies so they don't starve each other too much? My plan is to split the rising main below the stairs into two 22mm supply pipes - one for bathrooms, one for kitchen. DOWNSTAIRS - take 22mm direct to boiler (6m run), teeing 15mm off just before boiler to supply sink, washing machine and dishwasher. These would be throttled back in an attempt to keep the boiler best supplied. UPSTAIRS - take 22mm up and through bathroom area, teeing off in 15mm along the way for all supply reqs. 1st tee will supply small bathroom - basin, toilet and electric shower (toilet and basin throttled back). Theory here is in small bathroom you wouldn't be using the shower AND toilet AND basin at the same time. 2nd tee will supply bar mixer shower in large bathroom. 3rd tee will supply basin and toilet in large bathroom. Final tee/end will supply bath in large bathroom. Any help much appreciated!
For best results you would be better off installing an accumulator. A lot will depend on the demand with regards to your idea,how good do you want the system to run?
thanks for the reply plumberboy. Working adequately enough to put the property on the market would be the bottom line. If I were living there I would expect there to be some pressure fluctuation as different takeoffs are opened, but to be able to have the electric shower and the shower off the combi working simultaneously. I'd also expect there to be a few combinations of combined tap openings, appliance usage, shower usage etc. where supply is starved somewhere. I'm pretty much describing what happens in my current house on the combi system. It's not perfect in plumbing terms, but in real living terms day to day it is more than adequate. Would like to avoid the accumulator install if possible!
That's fair enough! If you're saying I won't see any noticeable difference between using 15mm instead of 22mm for the feeder pipes then I'll use 15mm throughout. If you're saying just whack whatever in and walk away then I can also see where you're coming from!
Hi Lube I think plumberboy has given you the answer you wanted and for what my opinion is worth I agree with him if you are selling the prop, for subtly different reasons. Its not the total number of outlets that determine the flow but the number of outlets used in one go vs the available head of water. For a given head of water available at the inlet of the property (and that varies depending on many factors) a pipe of a given diameter flows an amount of water and at the same time the flow causes friction that reduces the available pressure as it moves down the pipe. The faster the water tries to flow the greater the resistance to flow and its resistance to flow rises as a square. To simplify, for a given pressure and pipe diameter the pipe will only be able to deliver a certain finite amount of water before it slows to a trickle If the demand (open outlets) exceeds this quantity each outlet only get a percentage of the total. For a 15mm supply pipe (and most household supplies have a 15mm supply) it can deliver enough water to satisfy demand for 3/4 & 5 bed houses. Its only when those houses are occupied with people all wanting to use the available services at the same time that slower flow will be encountered. A double riser will help the situation as will running in 22mm but in both those instances you will still encounter high resistance in the common supply pipe and this may still limit the total volume of water available Keep it simple I think Hope this helps explain Russ
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