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I have a bit of a mental block understanding the difference between pressure and flow.
I need to replumb the cold water feed into our house.
Currently it comes into the cellar in a chunky lead pipe, adapts to 15mm copper to go through the water meter, then back to lead - after which it disappears into the wall cavity, never to be seen again* (its this bit I want to get rid of).
In my head, having reduced the pipe size down to 15mm, even briefly to go through the meter, there's no point in doing the replumb in 22mm, as the reduction in CSA, even briefly means the flow will have dropped, as the "head" from the street will be constant, and the reduction in orifice size will be just like turning a tap down.
Or am I missing something?
I basically want to end up with the pokiest shower possible. (combi boiler is quite chunkily sized for the house, so I don't see that as a limiting factor)
Would it be worthwhile trying to get the meter upgraded to a fatter one?
As an aside - any downsides to using Speedfit, long term? I've used it before in our old place (but we weren't planning on staying there forever), and I do have easy access to all the new proposed pipes.
Thanks!
*best guess is it goes up to the 1st floor through the wall cavity, to the bathroom at the back of the house (can't get the floor up without destroying it), T's off to the boiler in the spare room adjacent to the bathroom, then down to the kitchen and down to the cellar again, ending up about 30' from where the water meter is. I want to basically run it all backwards, then when we redo the bathroom (next project) disconnect the lead pipe hidden in the wall.
The chunky lead pipe is possibly less than the 15mm copper internally, especially with 100 years of limescale mixed in (YMMV)
Get a plumbers water flow cup (Amazon/Screwfix, etc) and have a play, it needs to be adequate for the boiler
We're in a low limescale area (S. Yorks) so I very much doubt that will be a problem.
The boiler is happy enough currently, and I doubt that anything I do will make it worse - its more about understanding if I can make it any better or if I'm chasing the impossible.
Not seen the flow cups before though - will probably invest...
IANAP however we do have lead incoming. Lead comes in different weights per foot so the external diameter doesn't tell you too much, but you can find conversion tables on pipe fitting manufacturers' websites
A 1/2" nominal lead pipe could have two different external measurements depending on the lead used. A 15mm copper pipe will be internally larger than 1/2" lead
Limescale is a good thing because it provides a protective coating against the lead. Lead in the water will also depend on your water pH
If you can, get rid of the lead supply and go from there
In my head, having reduced the pipe size down to 15mm, even briefly to go through the meter, there’s no point in doing the replumb in 22mm
Wrong, the pressure loss caused by a restriction is accumulative over the length of the restriction. So 22mm internal pipe work would result in less press drop / head loss.
However, in practice 15mm should be sufficient if your incoming pressure is good. The most likely restriction, as mentioned above is the lead incomer.
Talk to your supplier. They may replace the lead for free, many have a lead replacement program. You may also get them to measure the pressure in the street and at your meter (whilst the shower or taps are on) to demonstrate the pressure loss.
combi boiler is quite chunkily sized for the house, so I don’t see that as a limiting factor
Potentially wrong here too. Combis need to be sized to give a good shower. You only need 10kw or less to heat a house, but you need 30kw or more for a good shower.
Wrong, the pressure loss caused by a restriction is accumulative over the length of the restriction. So 22mm internal pipe work would result in less press drop / head loss.
Ah. Useful. And given that I'll be disconnecting 12-15m of 1/2" lead and replacing it with 10m of 22mm copper/plastic, that'll be a win then.
You only need 10kw or less to heat a house, but you need 30kw or more for a good shower.
Boiler is 42kW
The lead incomer is 24.3mm OD, so I'm guessing it's 1/2" ID at that point. Replacing the feed into the house itself isn't massively up the list of priorities, as it would involve digging up 15m of the front yard. I accept that it needs doing at some point though.
Looking (very) closely at the meter, it looks like its actually a 22mm one fitted with reducers on the pipes in and out. Easy to upgrade the outfeed then, but probably not worth doing the supply side as its probably already bigger than the lead pipe.
Starting to get a plan together.
Thanks!
as it would involve digging up 15m of the front yard
Not necessarily, you may be able to have it done using directional drilling / moling. You'll be responsible for the pipe from the edge of your property, your water supplier should replace any lead pipe before that. There may be grants available. Cost should be around £1000.
My father in law had it done purely to get better water pressure. Pipe came in under a stone wall (converted mill) and a concrete floor so trenching would have been horrendous. Directional drilling made it simple and increased pressure dramatically.
Not necessarily, you may be able to have it done using directional drilling / moling
Was just about to mention the same. We had ours done as an insurance job (old pipe was leaking) and it cost about a grand.
We had our water supply replaced using a mole about 15 years ago. the guys who did it were great and no digging except for a couple of very small check pits as it had a long way to go.
My father in law had it done purely to get better water pressure.
He'll have been disappointed then because the pressure won't increase but the flow will. Basically thee water will be at the same pressure but if the new pipe cross section is greater more water will come through at that same pressure.
He’ll have been disappointed then because the pressure won’t increase but the flow will
The pressure at the house end of the pipe will be closer to the pressure at the street i.e. higher, when a tap is open, because;
more water will come through at that same pressure
To replace the water that’s leaving the tap.
It’s by no means easy to get your head round it!
He’ll have been disappointed then because the pressure won’t increase but the flow will
No he wasn't, the old pipe was almost blocked, the pressure readings before and after vastly different. Think of it like a throttle - a small opening will have a big pressure drop across it, a large opening a small pressure drop.
In previous house that we gutted and renovated it had lead incoming / 15mm copper and stopcock / 15mm JG pushfit throughout house / 28kw Worcester combi condenser / 8" (or possibly 10") large Victorian style Rose shower head.
Full flow at full temperature was possible - no worries about flowrates.
Or
Fit a transition coupler on the lead riser as near to the point it leaves the ground.
Then plumb forwards from that in 15mm, either copper or jg speedfit.
If you are worried about flow then go 22mm, use swept bends amd then reduce to 15mm on the tap feed legs.
righto just replaced our original lead feed. you don't need to dig up your whole garden. just the bit right next to the main and the bit where you want to reconnect to your house. the rest can remain buried. ours diverted off somewhere under the law, no idea where, but we just cut in and reconnected. Still have some internal lead work I'm planning to remove as part of the next phase of work. I didn't notice any changes to water pressure from the change
Out of interest, if you're plumbing in a shower with 15mm inlets, is there a benefit in leaving it in 22mm right up until it needs to be reduced to fit?
Out of interest, if you’re plumbing in a shower with 15mm inlets, is there a benefit in leaving it in 22mm right up until it needs to be reduced to fit?
In theory yes, pressure will be improved, but in practice it may be marginal. On the flip slide, the time for hot water to arrive at the shower will be considerably increased due to the increased volume (just over 2x) of water standing in the pipe. My shower is fed by a pump from a vented cylinder and I actually wish I had plumbed it in 15mm for this reason.
Thanks!