If underground it may be cheaper to first reduce the 32mm MDPE to 25mm and then insert the necessary stop cock and tee off all in 25mm. Then convert the 25mm MDPE to 22mm copper further down the line above ground with straight couplers. 32 mm underground fittings can be expensive e.g. 32mm stopcock £86.98: 25mm stopcock £50.01 all plus VAT.

Posted By: owlmanIf underground it may be cheaper to first reduce the 32mm MDPE to 25mm and then insert the necessary stop cock and tee off all in 25mm.

Why does it matter if it's underground or not owlman?

Won't the water co want a say in where the meter goes?

This is the problem with having lots of different threads on closely related subjects: I'm fairly sure Shevek said something about his lot wanting their own meter for monitoring purposes separate from the water company's one but maybe it was somebody else and I, for one, can't be bothered to search.

It's a balance; from experience I know when I hit a subject with an all encompassing thread I often lose half of what I'm after, potential commentators switch off and I start being very military again with numbered lists and unfriendly looking re-direction. I think it is important to realise that this is a Forum for discussions not just Q&A and it's success is that is a source of info for watchers as well as participators. Accordingly, having most of the important info in one thread (a well named thread) is the first priority. I think, Shevek, that it would be more useful for all if your threads were more generic and that in future I will be quicker to start another, more specific, thread, if the generic one has drifted or lost interest. Just my tupeneth worth in a small thread where most won't see it

Posted By: barneyPersonally, I would bring the MDPE through totally unbroken to an internal location and then change to copper at that point and then fit the IV and meter (in that order unless you want the meter at the boundary for leak detection purposes of course)

Sounds like a plan.

I quite like focussed threads because the forum then becomes an easily searchable database. While long threads of broad subject matter are also good they can be very difficult to refer back to and search through. I'll try and tone it down though.

The meter is for our own monitoring purposes.

I've assumed we'll reduce from 32 mm to 22 mm but Barney mentions 28 mm pipe here:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=10826&page=1#Item_7

Given that we're planning to run two showers off a combi I guess we should probably reduce to 28 mm instead of 22 mm, run that to the 1st floor bathroom and then reduce to 22 mm for the en suite on 2nd floor?

It does look, however, like 28 mm water meters are harder to come by: http://www.jetrange.co.uk/technical-data/&id=107 http://www.elstermetering.co.uk/downloads/V100_Specification_Sheet_200411.pdf (mind you there's no 22 mm option either).

Sorry, after the original post, I've moved this to the "Plumbing: how to calculate appropriate sized pipes for dead legs" thread, where its more directly relevant...

Are non-return valves still needed at the point of entry to the property? I know that there are now a load of reg for non-return valves near things like showers over baths (or more-so if near toilets), but I was under the impression that the requirement had been dropped for NR valves next to the stop tap (except in the case of a shared main - like in flats for example).

I had my new water supply pipe inspected on friday prior to connection in the next two weeks. No NRV fitted. Just stock tap with drain off on a T above that. Fully insulated and ducted below garage floor...

Posted By: Shevek

Posted By: borpinI went from 32mm to 22 but wish I had gone to 28mm before splitting to H&C of 22mm.

Why is that? Not as much flow rate as you'd hoped?

Yes.

It may be the NRV is a Scottish thing.

Ask your 'Gas safe' installer :)
The boiler requires a minimum gas pressure at the gas valve inlet to satisfy the boiler when its on full power
, say 28kW , so as to create a safe burn , as with all pipework , you get a reduction in pressure relative to friction, resistance . So length of runs , number of bends etc. from gas supply point to boiler need to be calculated and pipes sized accordingly.
It does seem a little strange to go all the way to the boiler in 28mm (or 22mm) only to reduce it on the boiler input to 15mm. but this is common .I presume this last restriction is not considered to have that much effect as long as the main run is sized correctly

Posted By: ShevekWhat's the point of using 28 mm copper pipe if a gas boiler on takes 15 mm?

Isn't the discussion about the cold main? It supplies other things as well as the boiler.

I haven't done calcs yet but Barney mentions the possibility of running 28 mm from the HWS generator to first floor and then on in 22 mm to the second floor (we're running two showers off the boiler):
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=10826&page=1#Item_7

So I assume he's talking about running both hot and cold in (potentially) 28 mm here. So, question is, why would you do that if boiler inlet/outlet is smaller.

Most combis have 15mm pipework for DHW, because at the flow rates they support (they have a flow rate limited built-in usually something like 8 to 13 litres per minute - depending on size), the pipe losses for 15mm copper are usually negligible (and as has already been said, smaller pipes between the hot water source and the points of demand gives less wasted hot water).

It is worth running large pipes to supply the combi with cold water, since that doesn't contribute to wasted hot water, and also other things such as the kitchen cold tap, toilets etc. will take water from that pipe, so if you have a large cold supply pipe, then the dynamic pressure drop at the combi input will be minimised when you're drawing off cold water to other things (e.g. if someone flushes the toilet, you don't want the DHW flow rate to suddenly drop).

So I have a 24kW combi, with a 22mm supply pipe from the road (length 10 metres or so), until up close to the boiler. Pipes from the combi to points of use are mainly in 10mm PEX or 10mm copper.

But for all of this, you need to know your static and dynamic mains pressures, demand sizes, and do some pressure loss calcs, otherwise you're shooting in the dark (and may make your life difficult + waste money by over-sizing stuff).

If you can do analogue DC circuit design, then it's exactly the same principles:

pressure ~ voltage
flow rate ~ current
pipe friction ~ resistance
flow limiter ~ current limiter
pressure regulator ~ voltage regulator
accumulator ~ capacitor
static pressure ~ voltage at zero current
dynamic pressure ~ voltage at non-zero current (i.e. under the effects of "upstream" supply resistance).

The main difference is that the resistance of pipes goes up with flow rate (so somewhat more similar to an incandescent light bulb than a wire).