How to increase Incoming mains flow

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Hi there,

New to this forum so apologies if I ask any stupid questions! My question is about my mains cold water supply, which is shared with the flat below. I am having a loft conversion with shower room (which will be at the opposite end of the flat from current mains supply & boiler etc.)

Currently my mains flow is meaauring 14-18 litres per minute, depending on whether downstairs are using water at the same time. (I'm unsure of the pressure) I have a Worcester Bosch Greenstar 29cdi combi boiler serving one bathroom (with electric shower) to the rear of the flat.

My concern is whether the flow rate and pressure will be enough to run to the loft at the front of the flat for the new shower.

The mains supply to the lower flat is via 25mm blue poly pipe which then reduces straight to 15mm copper supply up to my flat, branching off to the lower flat supply about half way up. My question is, if this 15mm supply pipe was replaced with 22mm from the poly, would this then increase the potential flow to the upstairs flat and still have enough pressure to continue up to the loft and along to the conversion at the front? Would it also help with the water 'stealing' I currently experience when more than one outlet is being used at the same time?

Thanks for your patience!
 
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It'll partially depend on the pressure as well as the flow rate, but changing to 22mm would be the first step, and you'd want to continue it as far as possible into your property. But is it possible to continue the 25mm blue poly to the point that you then spilt for the 2 flats, and then take them in at 22mm.
 
Your boiler won't be able to run two showers at the same time - are you aware of this?
 
Think you would be better off with an independent mains water service,you dont (i hope) want your water alterations to reduce your neighbours water flow rate.

You may even have to get written permission from your neighbour depends on tenure and other agreements.

An experienced plumber on site (access to both flats req) would be able to work out if your alterations will reduce your neighbours flow rates if favourable results get this on paper,if negative consider an independent service.

Have seen this done, after alterations there was not enough shared flow rate to activate the neighbours combi boiler during times of demand from both flats,previously there was no water flow problems. The neighbour doing the alterations did not consult his ground floor neighbour It ended up in court and cost the offending neighbour a lot more £££ than installing an independent supply. Also they had to split the supplies to form independent supplies. Well thats London for you.
 
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Thanks all so much for you quick responses. Much appreciated. I'll try to answer your questions in turn....

It'll partially depend on the pressure as well as the flow rate, but changing to 22mm would be the first step, and you'd want to continue it as far as possible into your property. But is it possible to continue the 25mm blue poly to the point that you then spilt for the 2 flats, and then take them in at 22mm.

This might be possible- the poly cound continue for an extra 4 feet or so vertically before splitting, which I'm guessing could help flow to both flats?

Your boiler won't be able to run two showers at the same time - are you aware of this?

My current shower is electric and feeds directly off the cold mains supply. Would this still affect the hot water feed to a new shower in the loft, assuming we were somehow able to improve the incoming flow?

Think you would be better off with an independent mains water service,you dont (i hope) want your water alterations to reduce your neighbours water flow rate.

You may even have to get written permission from your neighbour depends on tenure and other agreements.

An experienced plumber on site (access to both flats req) would be able to work out if your alterations will reduce your neighbours flow rates if favourable results get this on paper,if negative consider an independent service.

Have seen this done, after alterations there was not enough shared flow rate to activate the neighbours combi boiler during times of demand from both flats,previously there was no water flow problems. The neighbour doing the alterations did not consult his ground floor neighbour It ended up in court and cost the offending neighbour a lot more £££ than installing an independent supply. Also they had to split the supplies to form independent supplies. Well thats London for you.

This was another concern of mine. I'll definitely consult a plumber (and the neighbours!) before deciding on any alterations. Thanks for the advice. Unfortunately I can't imagine how on earth a separate supply could be routed through to our flat without digging up the entire building (!) but I'll look into it.
 
An electric shower is only about 5-6 li/min which greatly reduces the demand on the incoming supply.

If you had another electric shower for your loft then that would greatly help the water supply problem. But then the electricity supply may not be adequate.

But you should read about flow rates. The open pipe flow rate that you have measured is not the same as the dynamic flow rate that you need to run showers.

Tony
 
This might be possible- the poly cound continue for an extra 4 feet or so vertically before splitting, which I'm guessing could help flow to both flats?

If you're getting 14-18l/min, then obviously you're also affecting the neighbours water supply, so R&Rs comments are pertinent, but as you are trying to resolve the issue for both parties, you're not going to (hopefully) get into the same problems. You haven't mentioned how many people are in the property, nor if the new shower would be usied at the same time as you're current set up, but it had to be a numpty that wetn from 25mm polly to 15mm copper, and then teed off of that for the downstairs property, so as you'd only need tio add 4ft of polly, then best to go to 22mm from the polly, and then put both supplies into that.
 
If you're getting 14-18l/min, then obviously you're also affecting the neighbours water supply, so R&Rs comments are pertinent, but as you are trying to resolve the issue for both parties, you're not going to (hopefully) get into the same problems. You haven't mentioned how many people are in the property, nor if the new shower would be usied at the same time as you're current set up, but it had to be a numpty that wetn from 25mm polly to 15mm copper, and then teed off of that for the downstairs property, so as you'd only need tio add 4ft of polly, then best to go to 22mm from the polly, and then put both supplies into that.

Thanks for the reply. The two showers will not necessarily be used at the same time but I would like it to be possible. (2 adults plus one 9yr old girl here so we'll need that option before too long...!) Downstairs is just one couple and we're on friendly terms with them so liaising shouldn't be an issue, and I've already mentioned the idea of replacing the 15mm with 22 from the poly in their flat.

Although I'd obviously rather not I'm wondering whether I'll need to upgrade the heating system to run a really good, powerful shower in the new loft bathroom with minimum difference to the rest of the flat, but am running round in circles researching all the options. As my current combi has only recently been installed I don't want to have to replace this so soon, and so would possibly be looking for a system that could run alongside it, bearing in mind that my flow isn't adequate for an unvented cylinder, apparently. Any suggestions gratefully received.

Thanks again.
 
Your boiler will provide 12.3Ltrs/minute of hot water, but that means that you may not get 6ltrs/minute for 2 showers as Muggles suggest, as that'll be ideal conditions; in the winter, when the incoming water is colder, then you may find both showers struggle. But if you have an electric shower in the current bathroom, and the combi just feeds the loft bathroom, then I think you should be fine, but check the water flow rates after the pipe changes, and that'll help you decide. But the pipe upgrade should also alow you to run an unvented cylinder, although you might have to juggle the hot water pipes so that the unvented cylinder feeds the showers, and the combi does the hand basins and sink etc.

But a lot of the more experienced guys here may have a better answer for you.
 
Your boiler will provide 12.3Ltrs/minute of hot water, but that means that you may not get 6ltrs/minute for 2 showers as Muggles suggest, as that'll be ideal conditions; in the winter, when the incoming water is colder, then you may find both showers struggle. But if you have an electric shower in the current bathroom, and the combi just feeds the loft bathroom, then I think you should be fine, but check the water flow rates after the pipe changes, and that'll help you decide. But the pipe upgrade should also alow you to run an unvented cylinder, although you might have to juggle the hot water pipes so that the unvented cylinder feeds the showers, and the combi does the hand basins and sink etc.

But a lot of the more experienced guys here may have a better answer for you.
Thanks for the suggestions, much appreciated. Will probably keep downstairs shower as electric and see how things look with new 22mm pipe from mains before deciding on the loft. I think my whole plumbing set up here is completely back to front anyway so may need a rethink (i.e. mains comes in to the bathroom so the elec shower and bathroom taps are first to T off, followed by dishwasher, washing machine, combi then kitchen tap) but at least the loft shower would be first T off the combi hot feed (before bathroom taps) although it would be a very long pipe run!
 
Actually, there's a lot to be said for your current setup in light of the dodgy mains flow. You'd want the best flow for the shower, and the other bits wouldn't matter how long they take to fill, but the 22mm feed should solve the problems, and you can leave the current setup as is. Consider a combi mate if you have a long run from the boiler though.
 
Actually, there's a lot to be said for your current setup in light of the dodgy mains flow. You'd want the best flow for the shower, and the other bits wouldn't matter how long they take to fill, but the 22mm feed should solve the problems, and you can leave the current setup as is. Consider a combi mate if you have a long run from the boiler though.
Great, cheers for the quick reply. Just a couple more questions for you if you don't mind? (sorry..!) Should I try and run the 22mm along the whole mains run, T'ing off to 15 where needed, or just run it in as far as the existing bathroom stop tap and leave the existing pipe work as is? (Much easier obviously! I'd continue the 22 up to the loft in either case)- Secondly, the combisave valve you mentioned, it looks like a great idea for a long pipe run, but does it reduce overall flow to all hot water outlets?
 
The further you go with the 22mm, the better cold flow all of the items will have. This'll mean you can fill the sink at the same time that the showers on, and not have any adverse effects, but the same won't apply to the hot taps. The combi save goes by the boiler, so will reduce the flow of water to anything hot, whilst the water is heating up, then it lets the water run freely.
 

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