Water main upgrade but with small 15mm section inline?

[mk2phil]

Hi all,

I'm hoping to upgrade my incoming lead water main with 32mm MDPE in an effort to increase the water flow. However, there would be a small section, 1 metre perhaps, where I need to drop it down to 15mm copper before it splits to service cold water outlets around the house, including combi boiler. My bath and shower (shower is a tap fed combi job) isn't great, and recently got worse do to what I suspect is a fault flow restrictor in the combi, which i'll check and fix accordingly.

My thought is that this will introduce a pinch point which will pretty much reduce the flow to what it already is now, and therefore largely pointless. I'd still be on 15mm into the combi for the last 1 metre, so assuming this is a somewhat pointless exercise?

Am I right in thinking that unless the entire run can be in the larger 32mm bore, it's a waste of time? I think 25mm is the standard upgrade size, but I'll gladly oversize to 32mm for the sake a few quid (assuming 32mm MDPR > 15mm copper is possible).

I'm also thinking about introducing a water softener, so if the upgrade WAS still worthwhile despite my reservations about the 15mm pinch point, I hope that 32mm would help to mitigate any flow/pressure drop as a result of having to pass through the softener en-route.

I am assuming that I can continue to run the MDPE under the floorboards into the house until the point I want to drop to 15mm. I'm wondering if I have to drop into 15mm at the point it enters the household?

EDIT: Main Combi 30HE rated at 14.1L/min @ 30C (12.1 @35C). I'm actually getting 8L/min from bath hot tap, and 12L/min from outside tap. Could one crudely assume that by upgrading from 15mm incoming to 32mm incoming, I could expect 24L/min? Double the pipe size, double the flow rate?

Any help is much appreciated gents.

 

[Taptom]

First rule of plumbing, as taught by my old Master Plumber gaffer - don't restrict your flow rates. The 15mm section will restrict all services downstream to whatever that section can supply for your supply pressure.

Find a way to size up to 22mm.

It's fine to run the water main under floor, but insulate the pipe and clip it to bottom of joists - stops the mice nibbling. Don't use any fittings before the internal stop valve. Use a full bore lever valve and I advise a pressure reducing valve with pressure guage. Put a t in just after the stop valve 22-22-15, a short section of 15 with stop valve acting as a drain off blanking the end just in case.

 

[Agile]

You are missing the point of pipe sizes!

You can get the same flow rate from a 15 mm as a 32 mm!

But the water has to move faster in the 15 mm and so there is more resistance to flow and that requires a higher pressure to overcome that resistance.

I don't understand why you think you must have a 15 mm section.

You can use 22 mm and have outlets of 15 mm connected to this.

Hardly worth a 22 mm connection to the boiler inlet. But it is usually worth having a dedicated 15 mm coming from just after the stopcock valve so that other water use in the house does not interfere with the pressure.

Much as I hate plastic pipe, it does have a lower flow resistance because it can mostly be fitted without elbows or fittings.

Tony

 

[JohnD]

Am I right in thinking that unless the entire run can be in the larger 32mm bore, it's a waste of time?

No.

Renewing most of the run will make a substantial improvement. But it will of course be better to replace the lot.

Are you perhaps thinking of the bit under the pavement? As you have got lead pipe, ask your water co for a Lead Content test TODAY and get it done before you start work. There may be a subsidy, or they may replace the first bit or they may do the connection at a reduced or even free price. They will have a leaflet or web page about their Lead Replacement scheme, though they may not widely publicise it.

 

[mk2phil]

Am I right in thinking that unless the entire run can be in the larger 32mm bore, it's a waste of time?

No.

Renewing most of the run will make a substantial improvement. But it will of course be better to replace the lot.

Are you perhaps thinking of the bit under the pavement? As you have got lead pipe, ask your water co for a Lead Content test TODAY and get it done before you start work. There may be a subsidy, or they may replace the first bit or they may do the connection at a reduced or even free price. They will have a leaflet or web page about their Lead Replacement scheme, though they may not widely publicise it.

Thanks for the response John.

I realised that I missed out some detail regarding the 1 metre 15mm section. I'm not referring to the water company run to my meter (bit under pavement), I fully intend on having them replace this section too, as you say using the lead replacement incentive.

What I was actually referring to was how my cold water main surfaces in my house. It's been extended with the kitchen and boiler placed in the extension. Original 15mm supply has been drilled through the original external wall into the extension, screeded over and then tiled, with a 15mm tail exiting upwards. From here it spurs as required, including a feed into combi, in 15mm.

So whilst I can in theory upgrade the pipe from my meter all the way into the house (would I go 32mm MDPE into house, connect to 28mm copper to run underneath floorbaords then down into 15mm, or possibly 32>28>22>15?), I cannot replace or re-route the last 1 metre. That would be the smallest diameter section, I would endeavour to keep the biggest supply pipe up until that point.

Thanks again, Phil

 

[mk2phil]

First rule of plumbing, as taught by my old Master Plumber gaffer - don't restrict your flow rates. The 15mm section will restrict all services downstream to whatever that section can supply for your supply pressure.

Find a way to size up to 22mm.

It's fine to run the water main under floor, but insulate the pipe and clip it to bottom of joists - stops the mice nibbling. Don't use any fittings before the internal stop valve. Use a full bore lever valve and I advise a pressure reducing valve with pressure guage. Put a t in just after the stop valve 22-22-15, a short section of 15 with stop valve acting as a drain off blanking the end just in case.

As per my explanation above, the 1 metre 15mm section is going through a wall and then screeded and tiled on the other side. I reason this is not a problem becuase my boiler can only accept 15mm incoming anyway, I couldn't run 22m into it for example.

When you say it's fine to run the water main under the floor, did you mean MDPE? I can't tell if there is a reg that says you must terminate into copper at the earliest convenience when it enters the property.

My alternative thought was to run vertical MDPE into a copper 28mm elbow, then horizontal 28mm run under floorboards to underneath stairs > 28>22mm stopcock, then 22mm all the way to the last 1 metre section where I reduce 22>15mm > boiler and spurs. Or 28mm all the way to 15mm, 28>15mm if it exists.

 

[mk2phil]

You are missing the point of pipe sizes!

You can get the same flow rate from a 15 mm as a 32 mm!

But the water has to move faster in the 15 mm and so there is more resistance to flow and that requires a higher pressure to overcome that resistance.

I don't understand why you think you must have a 15 mm section.

You can use 22 mm and have outlets of 15 mm connected to this.

Hardly worth a 22 mm connection to the boiler inlet. But it is usually worth having a dedicated 15 mm coming from just after the stopcock valve so that other water use in the house does not interfere with the pressure.

Much as I hate plastic pipe, it does have a lower flow resistance because it can mostly be fitted without elbows or fittings.

Tony

Hi Tony, sorry my mistake in not clarifying why I have the 1 metre in 15mm. I've described this now in my previous replies here; it's goes through an external wall into extension where it has been screeded and tiled. Tail comes out of the floor into stop tap, from there it spurs as necessary to taps and boiler.

So I can in theory replace everything up until this last 1 metre of 15mm. I'm not choosing to do it, rather working around it and asking whether I should even bother considering i'll have a pinch point on the run that is 15mm which I mistakenly thought would cancel out any benefit of having the pipe until that point run in 32mm MDPE (or possibly 32mm MDPE > 28mm copper > stopcock > 15mm).

Seems as though I would still see a large benefit, but not the maximum benefit due to the 1 metre 15mm section. Fine, I can live with that, don't have a choice really.

Although now I do need to understand the best way to pipe it up when it enters the house.

I could try and continue the 32mm run all the way through the house - with stopcock in between or at the end as necessary - up until I physically have to drop to 15mm, OR

Run 32mm MDPE into house, then elbow onto 28mm copper, then run the 28mm copper as far as I can before I have to drop to 15mm.

I suppose I could even 32mm MDPE > elbow > 28mm copper > 28/22mm stopcock > 22mm run > 15mm reducer > 15mm 1 metre run to boiler (with spurs AFTER the direct boiler feed is taken)

 

[Taptom]

Unless you live in a mansion which you don't since you've got a combi,or the supply pressure is really **** poor, there really shouldn't be any need for any 28mm piping for water. We use 28mm copper in domestic houses principally to supply sufficient gas for the ever more powerful combis now available. 22 pipe will be enough for water.

 

[mk2phil]

Unless you live in a mansion which you don't since you've got a combi,or the supply pressure is really **** poor, there really shouldn't be any need for any 28mm piping for water. We use 28mm copper in domestic houses principally to supply sufficient gas for the ever more powerful combis now available. 22 pipe will be enough for water.

So 32 > 22 > 15 is the best way to go.

If 22mm is enough for water, then I would in theory be perfectly fine only using 25mm MDPE on incoming main (even though I will use 32mm regardless)?

 

[JohnD]

the new pipe does not have to go in the screed. In a kitchen, you can probably clip it to a wall behind units. In a utility room, it doesn't matter if it's visible.

I don't know what the pro's will say, but I thought it better to run the new polypipe all the way to the kitchen stopcock, as it is reasonably flexible when going under floors and through walls and needs no bends, joins or elbows.

If you tee off the big pipe for your bathroom, boiler, utility, kitchen, garden tap, there will be less loss of flow in one outlet when you turn on another. If you neck it down to 15mm before you tee off, and especially if you fit the small stopcock, there will be more interference. Each pipe size has about double the capacity of the next smaller size.

Because of the wall thickness, external diameter of each size of blue pipe is bigger than the copper pipe of (just about) the same internal diameter. So 20mm blue matches 15mm copper; 25mm matches 22mm, 32mm matches 28mm

 

[mk2phil]

the new pipe does not have to go in the screed. In a kitchen, you can probably clip it to a wall behind units. In a utility room, it doesn't matter if it's visible.

It's not that, it's all open plan between the lounge and kitchen. I cant physically get to the corner of the room in 22mm unless I go via the first floor then drop down into the corner. In fact, can't do that either because the toilet is above, and that's tiled too.

Pretty sure it doesn't matter because my combi can only accept 15mm, so the only benefit would be the last metre where the flow would have benefitted from also being 22mm. Can live with that, not much choice.

 

[JohnD]

is there scope to trench the new pipe in a different route, for example in the garden?

 

[mk2phil]

Not really, would have to dig up concrete in a shared driveway to do that.

 

[Agile]

You should do your best to keep the pipe size as large as possible so that it contributes negligible flow resistance.

Your 15 mm is a very high resistance.

If you possibly can you should try to replace it.

Just why can you not cut a channel along the floor?

Tony