16 mm or 20 mm MLCP for combined bath/shower fill?

[markocosic]

I have a run of 8-10 m from an UVC to a bath filler / shower mixer. No fittings en route as planned. Given free choice would you use 16 mm or 20 mm MLCP?

 

 

We are thinking this unit for BOTH bath fill and shower:

https://www.hansgrohe.com/articledetail-ecostat-bath-thermostat-1001-cl-for-exposed-installation-13201000

https://online.depo-diy.lt/product/181956

 

(easy to service / swap)

 

 

I have a choice of 16 mm or 20 mm MLCP (the brackets come equipped for either / or)

https://online.depo-diy.lt/product/23810

https://online.depo-diy.lt/product/23812

 

 

Notional flowrate of fixture 20L/min @ 3 bar bath filling or 16L/minute showering. (presumably that's the valve not the handset though)

 

 

Will 16 mm be an appreciable restriction / will it make an appreciable noise at those flowrates?

 

Or asked another way is there any reason not to use the 20 mm? 

 

Where it's running through studs / battens would you sleeve it / wrap it / foam it to reduce noise or just pop it through a hole slightly larger than the pipe itself?

 

 

Supply pressure is fine. (borehole pump maintains 3 bar up to 40L/minute on a 32 mm MDPE incomer)

 

 

[JohnMo]

You don't need any bigger than 16mm. The bigger the pipe the more volume of hot water you need flow through before you get hot out the end you want it.

 

 

[markocosic]

Thanks @JohnMo

 

MLCP book of words suggests pressure drop is ~0.3 bar for 20/min at 10m; say 0.4 bar allowing for fittings that make the effective length more like 13m

 

You don't think the flow will be audible then?

 

I have 15 mm PEX (similar ID to 16 mm MLCP) to a bath filler in the other house l, which is both noisy and annoyingly low flow rate; so wanted to sanity check.

 

It's also going through a combi and what is probably a lower flow fixture with naff mains pressure (incoming main 1/2" copper with a meter cut into it) 

 

The volume difference is meh for a shower IMO. Warming the pipe/valve/shower head takes the time; not purging the pipework.

 

More critical for the handbasin/kitchen tap though.

[Nickfromwales]

9 minutes ago, markocosic said:

I have 15 mm PEX (similar ID to 16 mm MLCP) to a bath filler in the other house l, which is both noisy and annoyingly low flow rate; so wanted to sanity check.

That will be zero to do with the pipe IMHO, and everything to do with poor internals of the valve itself. A full-bore isolation vs a horrid Ballofix valve is chalk and cheese.

 

16mm pipe is plenty if off a combi. I'd only go 22mm if off an UVC etc.

[markocosic]

Would you sleeve through joists at all?

[Dan F]

What shower flow rate did you want/expect?

[markocosic]

Shower probably 8-10L/min?

 

It's the bath fill that'd be nice to have not take an age. And both to not make a noise.

 

I'll put an ear to some fittings I think.

[Dan F]

8 hours ago, markocosic said:

MLCP book of words suggests pressure drop is ~0.3 bar for 20/min at 10m;

Which book is that?   16mm Geberit MEPLA (which is what we used) has 0.9 bar loss over 10m at 18L/min.  18L/min is the max recommended flow for 16mm, as they recommend keeping velocity at <3m/s (but higher than for copper).

 

In reality though, if your design flow rate 12L/min and your hot water tank is at 48C, then you'll only need 10L/min hot water.  In this case, the loss seems to be more like 0.3 bar, yes.

 

[HughF]

The issue with 16mm is the internal bore of some of the fittings. I use 16mm mlcp wherever I can, but I always try and minimise the fittings count, as they are restrictive.

[Dan F]

17 hours ago, HughF said:

The issue with 16mm is the internal bore of some of the fittings. I use 16mm mlcp wherever I can, but I always try and minimise the fittings count, as they are restrictive.

Tell me about it!  Our plumber hadn't used MLCP before (or at least it seemed that way) as he installed shower runs as if they were copper with fittings everywhere, rather than bending the pipe.  This was with the MEPLA fittings, which are even narrower than some of the other brands, so, with a 12m 16mm run and 5->6 of the 90-degree fittings, we'd had got minimal flow rate from the shower.  Had to take some photos and send them to Geberit technical who confirmed that it wasn't going to work and not designed to be used like that, to convince the plumber (with the help of the main contractor) to redo things.   I've still got the photos somewhere, which were quite assuming..

Edited July 13, 2023 by Dan F

[HughF]

2 minutes ago, Dan F said:

Tell me about it!  Our plumber hadn't used MLCP before (or at least it seemed that way) as he installed shower runs as if they were copper with fittings everywhere, rather than bending the pipe.  This was with the MEPLA fittings, which are even narrower than some of the other brands, so, with a 12m 16mm run and 5->6 of the 90-degree fittings, we'd had got minimal flow rate from the shower.  Had to take some photos and send them to Geberit technical who confirmed that it wasn't going to work and not designed to be used like that, to convince the plumber (with the help of the main contractor) to redo things.   I've still got the photos somewhere, which were quite assuming..

I've got a 16mm bender, I always try and bend as much as possible.

[Dan F]

5 minutes ago, HughF said:

I've got a 16mm bender, I always try and bend as much as possible.

 

Then, on top of this, there were going to add more 90deg fittings in between the joists:

 

 

Edited July 13, 2023 by Dan F

[HughF]

Blimey...

[markocosic]

"What are you seeking to achieve?" is always a good question.

 

On reflection here are a few data point and decisions to remind my future self. May be of use to others.

 

In short yes; 16 mm is ok; if the run is modest and the fitting count is a total of two. (one off the manifold and one at the bar mixer) 🙂

 

 

I like is this shower:

 

 

Notionally 16L/min @ 3 bar (at the handset)

 

In the apartment it delivers 12L/min after taking the wallbox and pressure drop in the supply (20 mm MLCP) into account. Dunno what supply pressure is other than "decent enough" [to direct feed much taller apartment buildings direct from the mains without booster sets]

 

Writing says Hansgrohe P-IX 28504/IB

https://www.banemo.de/582742/hansgrohe-croma-select-e-handbrause-1jet-weiss/chrom-26814400

 

Current version:

https://www.hansgrohe.com/articledetail-croma-e-hand-shower-110-1jet-26814400

 

 

I'm not astoundingly keen on is this:

 

 

Notionally 9L/min at 0.5 bar (at the handset)

 

https://www.mirashowers.co.uk/showers/mixer-showers/mira-atom-ev/

https://resources.kohler.com/plumbing/mira/pdf/1421588-w4-a-mira-atom-ev-datasheet.pdf

https://resources.kohler.com/plumbing/mira/pdf/1393515-w2-a-mira-ev-thermostatic-bar-valves-v2.pdf

 

Should be ok on paper.

 

I suspect incoming main in 1/2" copper; water meter; combi boiler not set to the "optimal 65C" that the manual suggests; and another 10 metres or so of 15 mm PEX kills it.

 

The bath fill is equally naff. But it's always going to be with a 24 kW combi.

 

 

Took a holiday.

 

6 of us in a cabin with a single bathroom; bar mixer; and an 80 litre tank with 1.5 kW immersion set to only slightly below boiling. It worked out ok; stored water wise. The immersion would just about keep up if folks weren't ridiculous in the shower. And if the shower weren't ridiculous. I should keep that in mind given the intended use of this place (summer house / one bathroom but potential for back to back use for a while)

 

One thing you can do with a cylinder, that you can't with a combi, is start and stop the shower without it being an inconvenience. Much easier to take a short, long, shower if you can start and stop the water inbetween soapings without having to wait 30 seconds with 10C water splashing about and cooling your feet every time you restart.

 

 

 

So.

 

We'll buy the bar mixer.

 

A faster bath fill might be nice but it isn't worth the faff / it's not like folks will be in a rush in this place.

 

https://www.hansgrohe.com/articledetail-ecostat-bath-thermostat-1001-cl-for-exposed-installation-13201000

https://online.depo-diy.lt/product/181956

 

 

Pipe and drops?

 

If hand shower were genuinely 16L/min; off a cylinder at heat pump temperature (50C?) and water at borehole temperature (5C) then:

 

https://www.spiraxsarco.com/resources-and-design-tools/calculators/water-mixing/water-mixing

 

0.2 L/sec gives 1.77 m/sec and 3.5 kPa/metre pressure drop for 16 mm MLCP by this book of words: (0.35 bar for 10 metres)

https://www.multipipe.co.uk/images/MUL056-Multipipe-MLCP-Technical Guide.pdf

 

If hand shower were 12L/min at the handheld after the various pressure drops and the cold feed were 15C (cold probably more like 15-20C given it will have been sat in a de-ironing / softening filter setup for a while) we're at 0.15L/sec; 1.33 m/sec and 2.1 kPa/metre. Fine in 16 mm MLCP.

 

 

Bath fill worst case would be:

 

A straight 20 litres/min hot would indeed be 0.3 L/sec for 2.65 m/sec or 7.2 kPa/metre. (0.7 bar for 10 metres). Too much for 16 mm MLCP. Thanks @Dan F - I'd indeed read 0.2 L/sec = 20 litres/min 😮

 

The cylinder does say that stratification is affected beyond 12L/minute though. If it were actually a 16L/min fill then that's probably about 12L/min at the cylinder; would maintain stratification; and only 0.35 bar per 10 metres on the pipe. So viable. Takes 15 minutes to totally rinse the cylinder @ 12L/min instead of 9 minutes @ 20L/min. Both are as good as forever. So 16 mm it is.

[markocosic]

Kitchen tap.

 

I like / have chosen the IKEA Almaren.

 

If you pull the flow restrictor (vid/link below) it'll do 10L/min on pure hot or pure cold on the same supply that the HansGrohe shower does 12L/min on. 

 

That's 0.167 litres/sec; or expressed another way 6.6 seconds to purge 10 metres of 16 mm MLCP that holds 0.11 litres/metre from cold.

 

If you're happy to whack the tap full hot open then dial it back to something reasonable to wash your hands etc (you have to - mixed flow is about 13L/min and would splash EVERYWHERE) you can be lazy about the hot pipe run / not go out of your way to find 12 mm MLCP etc. (sheds don't sell less than 16 mm MLCP here)