Increasing dhw pressure to attic room

Hi everyone. Merry Christmas

I have a 6 bed house (rented) on 3 floors plus a cellar with a vaillant 937 combi boiler. All the hot and cold pipes are in 15mm and the middle and attic rooms get zero water, not a drop if somebody has a shower on middle floor. It started off as one shared bathroom and 6 kitchenettes when I did it 15 years ago but now there are 3 bathrooms and same kitchenettes So it’s quite a problem.

I know in due course this will get upgraded to a system boiler and 300 ltr indirect invented tank but for now the 300 tank yet to be installed will run off the combi. For this new tank pipe work will need to be upgraded so I’m addressing this problem anyway.

im about to put 28mm pipe for dhw and cold from boiler/mains and then get to first floor and reduce it to 22 then 15 right up to taps. All the way to 3rd floor bathroom.

The question I have is this. The old circuit of 15mm that will now be redundant shall I just cap it off or should I Tee the new 22mm pipe into it to have constant hot water circulating around. I’m worried about backflow and drop of pressure so reluctant to do it but then I’m also aware the top floor shower will have to wait about 5 min for hot water to run through. Thank you for your help.

Anybody got any ideas?

Are you currently running the cylinder off the combi bit of the boiler? Bit tricky if the cylinder goes cold, you'd waste a lot of water. And when you say no water on the top floor is that cold as well as hot or just hot?
Have you done a proper pressure/flow test where your water main comes into the building- if the supply pressure is low then bigger pipes aren't going to help much. If you're running off a cylinder to that large a property then yes keep the circulating loop, it'll reduce your legionella risks (if you have blend valves at every bathroom/kitchenette so the pipe temperature stays at 65 or above)

oldbutnotdead said:

Are you currently running the cylinder off the combi bit of the boiler? Bit tricky if the cylinder goes cold, you'd waste a lot of water. And when you say no water on the top floor is that cold as well as hot or just hot?
Have you done a proper pressure/flow test where your water main comes into the building- if the supply pressure is low then bigger pipes aren't going to help much. If you're running off a cylinder to that large a property then yes keep the circulating loop, it'll reduce your legionella risks (if you have blend valves at every bathroom/kitchenette so the pipe temperature stays at 65 or above)

Click to expand...

actually the tank isn’t ready yet. As in not installed but it will be soon. I’m just upgrading pipes first.

No hot water at all on top floor when a shower being taken at middle floor.
I’ve not done a pressure test outside. Is that something I should do first?

Circulating loop is that the old pipes that I should tee into. Won’t that reduce pressure??

Yes you should definitely check pressure and flow rate at the point where the service pipes enter the house (or as near as possible)- there's no point shelling out for this new cylinder etc if the mains water pressure isn't up to the job. Do consider that if your water supply is showing 1 bar in the basement and your 3 storey house is 12 metres from basement to top of 2nd floor shower (I've assumed here you have English 3 storeys- ground, 1st, 2nd) then you will have zero cold water pressure at the top of the 2nd floor shower.

I assumed from your original post that you currently had a circulation loop on the hot water- if you don't then yes it would be worth linking the original 15mm pipe run to the new DHW pipe run at the top of the house. Not sure exactly how it would work on a pressurised cylinder (I'm not G3 so not qualified to work on them), on trad vented systems with a header tank you'd have a small pump on the 15mm return line driving into the bottom of the cylinder (and a non-return valve between that return and the feed from the header tank). All this pump will do is circulate the water from the tank up the new pipe run and back down the 15mm, for a small domestic setup it is well worth using a pump designed for the job (low speed low noise 'learns' hot water use). When someone opens a tap the volume of water in the system decreases allowing the non-return valve to open & header tank to drive hot water up the main run to the tap. You've just given me a thought- I wonder if one of these pumps is clever enough to sit in the feed rather than the return, tick over gently when there's no system demand but crack on the revs when someone opens a tap. Hmmmmmm.....but that won't help you. Or maybe it would- though I think water suppliers frown on pumped extraction directly from their supplies

Presumably the cylinder will be going in the cellar with the boiler? If so then yes the volume of water between cylinder and shower may give a significant delay for hot water (and use a significant amount of water). Doubt it would be as much as 5 minutes though. Consider- a metre of 15mm contains 1.5 litres, a metre of 22mm contains 3.5 litres, a metre of 28mm contains 5.7 litres. A good shower flow rate is 15 litres per minute (0.25 litres/second). Let us assume that your run from cylinder to top floor is 4 metres of 28mm (basement-ground), 4 metres 22mm (ground-1st) and 12 metres of 15mm (1st-2nd plus run from service void to shower). So you have a volume of 23+14+18= 55 litres to shift- which is about a bit shy of 4 minutes, I stand corrected.

Options.
Loads, depends very much on how much space you've got. I'm not going to get into pressure drop calcs this time of night but there might be some advantages to having a manifold from your cylinder and separate pipe runs from that manifold to the bathrooms. 15mm to the 3rd floor only might be iffy, 22mm would almost certainly work but you'd need to do some sums to check. 22mm from cylinder to 2nd floor then 15mm to shower would give you 28+18 = 46 litres- 3 minutes. Still not good enough (and that's ignoring flow losses in the pipes which to be fair the base plan does as well).

Is there any scope to put the cylinder in the middle of the house (1st or 2nd floor). Or (this might not be cost effective with pressurised cylinders) is there any scope to install 3 smaller (150l) cylinders local to each bathroom?

Since this unvented system is going to have to be installed by someone qualified, I'd suggest you get a few companies in to have a look at the job and advise- a good design will achieve far more comfort that just chucking something in. Interesting project though, do keep us informed

Wow. Thank you you’ve given me lots to think about. Thank you. Ok first thing I’m gonna do is start digging up the outside path and see the lead pipe coming in. Just at the entrance of house it’s lead then changes to 22mm copper. I was thinking of upgrading at this point to 28 and then running 28 as far as I can (at least 10meters) before reducing to 22 to go upstairs)

but now it seems you’re recommending that I upgrade or at least check the pressure outside the house with Yorkshire water. I’ll do that. Thank you

If you're thinking about redoing your cold water supply you could get the water company to replace the lead supply to your property (for free). That might (just a guess) get you a better supply at the same time.

https://contact.yorkshirewater.comh...-supply/what-is-your-lead-replacement-policy/

If you've still got lead supply pipe then replace it - most water companies will connect your replacement pipe from your boundary to the street main FOC (but the replacement pipe has to be buried to their specs). While you're at it, best to replace the buried copper so there's one single run of MDPE from street stoptap to your internal stoptap. For your uses i'd put 32mm in as a minimum, maybe go to 50mm (pipe is cheap).

Thank you everybody for your replies. I didn’t touch the pipe Coming from outside. It seemed big enough and water pressure downstairs in kitchen was great so seemed little point in starting there. I ran 22mm pipe all the way up to attic for hot and cold. The kitchen went from 22 to 15 into the cellar so where I could I upgraded from 15-28 mm horizontally until I reached the point (across two rooms) to connect into the 22mm vertical run. Along the way I noticed the old 15mm had too many unnecessary and kinked 90 degree bend where the previous plumber wasn’t bothered and neat cornering. well the water pressure is like a fireman’s hose now so all good. Thanks for your comments