Passive house plumbing first fix - any tips

[Nickfromwales]

47 minutes ago, markharro said:

My better half has her heart set on what will be a shower capable of a very high flow rate. More than I think 15mm will service. If she persists with this would this need its own radial supply or higher bore than 15mm with another 10mm for the basin?

Defo 2x radials, but 15mm to the shower will be fine. I fitted a crica £2k Hans Grohe shower in a clients build and the water flow from it was just silly (huge amounts). I did install a 300L cold mains accumulator there though, so you may want to consider space to retro-fit this if the shower dips when a tap is opened elsewhere in the house simultaneously. 

[markharro]

11 hours ago, Iceverge said:

Our shower at 10l/min is more than adequate for Mrs and she has very thick hair. 15mm for the shower. 

 

I would keep all basin hots as dedicated 10mm runs

Thanks for further advice. Still not clear what to do if you need a 10mm feed to a basin and 15mm (or larger) to shower in same room? Looks to me that you really need two separate pipes feeding that room to provide for this?

Ah since writing this I have just read @Nickfromwales answer to this very question. Ok so this accumulator tank - this would need to be located in the shower-room would it? Don't fully understand the need for it...why just cold for example? would there not also be an issue if someone used a hot tap at the same time?

Also would running 22mm hot and cold to the shower - its not a long pipe run for us - avoid the need for a tank like this?

Edited August 6, 2023 by markharro

[markharro]

Another point - someone else has mentioned that for microbore radial you need sufficient mains water pressure. What is sufficient and how do I measure our water pressure?

[Thorfun]

2 hours ago, markharro said:

Still not clear what to do if you need a 10mm feed to a basin and 15mm (or larger) to shower in same room? Looks to me that you really need two separate pipes feeding that room to provide for this?

sounds like you're after a form of hybrid radial system with one big pipe to a room and then tees off from that to each tap. I have run a 15mm pipe from our plant room to every single tap for hot and cold. that's why my manifolds are so big and I have so many pipe runs. I did consider the hybrid approach but I really didn't want all those joints behind the walls and also wanted to be able to isolate from a central location an individual tap/outlet if required rather than scrabbling about behind/under units to try and turn an outlet off with a local isolation valve.

[Nickfromwales]

4 hours ago, markharro said:

Another point - someone else has mentioned that for microbore radial you need sufficient mains water pressure. What is sufficient and how do I measure our water pressure?

https://www.screwfix.com/p/monument-tools-mains-water-pressure-test-gauge-11bar/82412?kpid=82412&cm_mmc=Google-_-Datafeed-_-Tools?kpid=KINASEKPID&cm_mmc=Google-_-TOKEN1-_-TOKEN2&ds_rl=1244066&gclid=Cj0KCQjwib2mBhDWARIsAPZUn_nCdrUSQHC88zTNOQI8V5NfpgJIhXydzHSQnpCFQWeV3Y66aEvcMT0aAks0EALw_wcB&gclsrc=aw.ds

 

Whack that on the outside tap / washing machine feed etc. It's 3/4" so you'll need an adaptor to get onto 15mm pipe or a 1/2" thread. You'll need to put a double-check non return valve on this and leave it overnight. The non return allows you to capture the highest 'peak' pressure available ( usually around 2-4AM ) to survey this correctly for an accumulator. Accumulators live in the plant room, or garage, utility space etc as these are nominally 200-300L, so quite big.

[markharro]

On 06/08/2023 at 15:33, Nickfromwales said:

https://www.screwfix.com/p/monument-tools-mains-water-pressure-test-gauge-11bar/82412?kpid=82412&cm_mmc=Google-_-Datafeed-_-Tools?kpid=KINASEKPID&cm_mmc=Google-_-TOKEN1-_-TOKEN2&ds_rl=1244066&gclid=Cj0KCQjwib2mBhDWARIsAPZUn_nCdrUSQHC88zTNOQI8V5NfpgJIhXydzHSQnpCFQWeV3Y66aEvcMT0aAks0EALw_wcB&gclsrc=aw.ds

 

Whack that on the outside tap / washing machine feed etc. It's 3/4" so you'll need an adaptor to get onto 15mm pipe or a 1/2" thread. You'll need to put a double-check non return valve on this and leave it overnight. The non return allows you to capture the highest 'peak' pressure available ( usually around 2-4AM ) to survey this correctly for an accumulator. Accumulators live in the plant room, or garage, utility space etc as these are nominally 200-300L, so quite big.

 thanks @Nickfromwales so you are saying fit https://www.screwfix.com/p/double-check-valve-15mm/96336?tc=RT5&ds_rl=1249404&gclid=Cj0KCQjwz8emBhDrARIsANNJjS786F2p-nDwkca2mK19l9MeyD-BzcY6oaRzmxrcnsNSY_TP4tId0hMaApbpEALw_wcB&gclsrc=aw.ds this type of thing between the tap and the pressure gauge?

 

What do you mean survey for an accumulator? 

[Iceverge]

On insulating the pipes. 

 

We had massively over dimensioned pipes installed originally by the plumber. 

 

This resulted in huge amounts of water sitting in the pipes that had to drained out of the tap before any hot water arrived. I initially tried to insulate my way out of this. Adding up to 30mm of pipe insulation in places. Tightly fitted and taped. It made almost zero difference. If you ran a tap and did the same 20 minutes later the water in the pipe had cooled to near room temp resulting in equally long hot water wait times. 

 

Far more important I think is to have minimal water in the pipes in the first place as that heat is lost anyway in a few minutes . The cylinder itself and closely connecting pipework(especially copper) looses heat all day, every day. 

 

I would take lots of care to insulate any tank fittings, especially copper and make sure nothing can heat via convention other than your hot water manifold. 

 

 

Looking at ours the hottest spots are a Brass blanking plug in the centre. A T+P valve on the right of the tank and a hot water pipe (uninsulated) for the shower in use at the top of shot. 

 

This is worst case for the pipe and will only be for 20mins per day. The brass blaming plug and T+P valve will be like this all day.

 

 

[Nickfromwales]

11 hours ago, markharro said:

What do you mean survey for an accumulator? 

An accumulator is like a battery, and it’ll charge up to the max “power” that it has available. Cold mains enters your house at higher static pressure at certain times of the day (usually higher overnight at 2-4AM) so those are the peaks that you’d want to harvest in the accumulated volume of stored energy (water pressure) for use when you wake up with the rest of the world and they use the water ergo you’ll otherwise suffer lower pressure at peak times. 
To maximise stored volume in the accumulator you need to adjust the back-pressure in the vessel to allow the water in, so you need to know max pressure so you can set the pre-charge accordingly.