Using Manifold-system and PEX piping for Central Heating and Domestic Water supply

[ZenMad]

Hi experts,

 

I'm new here, and want to start of saying that I'm not an expert in plumbing at all.

 

We're doing a full home renovation. As we are stripping the entire house and changing the layout we are also planning on getting the entire central heating system and domestic hot water supply removed. Being from Belgium, where manifold-systems with PEX pipes are the norm, I want to get a similar setup in my house. What can I say: I like the control they provide. 

 

I've spoken to a few plumbers already, but to my surprise copper pipes and branch-systems are still widely popular and most plumbers I spoke to are unfamiliar or inexperienced with what I'm enquiring after.

 

Here's a bit about the house:

- 3 floors

- Downstairs 110 sqm (living room / kitchen / hallway / toilet / garage)
- First floor 65 sqm (bathroom / 3 bedrooms)

- Loft 35 sqm (bathroom / 1 bedroom)

 

There are a total of 10 radiators (3 on ground floor, 4 upstairs, 3 in loft) plus under floor heating throughout the entire ground floor.

 

There is a combi boiler in the garage. 

 

Simply put what I'm after is 6 rows of manifolds :

- Row 1: Water supply branches off and goes (a) into boiler and (b) into DCW manifold. This manifold (chain) has 15 outlets (with valves) that go to:

1. Toilet (downstairs)
2. Toilet sink (downstairs)
3. Toilet bathroom (first floor)
4. Bathroom sink (first floor)
5. Bathroom bath (first floor)
6. Toilet bathroom (loft)
7. Bathroom shower (loft)
8. Bathroom sink (loft)
9. Kitchen sink
10. Kitchen dishwasher
11. Kitchen icemachine
12. Dog shower (garage)
13. Washing machine (garage)
14. Garden watering system
15. Outside tap front of house
16. Outside tap back of house

- Row 2: DHW from combi boiler enters DHW manifold. This manifold (chain) has 7 outlets (with valves) that go to:

1. Toilet sink (downstairs)
2. Bathroom bath (first floor)
3. Bathroom sink (first floor)
4. Bathroom shower (loft)
5. Bathroom sink (loft)
6. Kitchen sink
7. Dog shower (grage)

- Row 3: CH flow enter CH flow manifold. This manifold (chain) has 10 outlets (with valves) that go to:

1. Bedroom 1
2. Bedroom 2
3. Bedroom 3
4. Bathroom (first floor)
5. Bathroom (loft)
6. Loft radiator 1 (loft)
7. Loft radiator 2 (loft)
8. Extra radiator 1 living room (to boost UFH)
9. Extra radiator 2 living room (to boost UFH)
10. Extra radiator kitchen (to boost UFH)

- Row 4: Same setup as Row 3 for CH return.

- Rows 5 & 6: UFH manifolds.

 

I'm fine with using copper around the boiler, but for all water (CH & DW) leaving all manifold outlets I want to use PEX piping with press-fit connections.

 

Would love to get thoughts on this? And hear out any concerns that folks might have? Like I said, it's been hard getting good input from plumbers.

 

Thanks in advance for you input.

[sharpener]

There's a lot of relevant discussion on this thread.

[ZenMad]

@sharpener thanks for sharing. That's only partially relevant though. I'm not as much enquiring whether copper or PEX is better. I'm pretty set on using PEX. I was mostly asking for feedback on the setup I had in mind, and if there are any concerns with that one or whether there are any other suggestions from folks (e.g. size of pipes, specific combinations, things to watch out for, limitations, ...). I did hear that @Nickfromwales seems to be the expert on those kind of setups, but I assume others here are experienced on using PEX piping and manifold systems. 

Edited March 9 by ZenMad

[sharpener]

I think it became clear from that thread that ppl on here are much more clued up about the benefits of PEX pipework than the average plumber. Good luck with your project!

[JohnMo]

2 hours ago, ZenMad said:

There is a combi boiler in the garage. 

 

Simply put what I'm after is 6 rows of manifolds :

- Row 1: Water supply branches off and goes (a) into boiler and (b) into DCW manifold. This manifold (chain) has 15 outlets (with valves) that go to:

I did something similar to you, but slightly simpler. All plastic pipe (almost)

 

Cold water entered house, tee one side to cold water manifold the other to the combi. Ran to combi in 22mm and then reduced down. Ran a single cold pipe into each wet room then branched inside the wet room in 15mm

 

Hot water came from combi in 15mm to manifold and then one hot pipe to each wet room and then branched in the room as per cold. Each run from manifold in 15mm. 

 

Keeps number of pipe runs down, simpler, cheaper, same functionality.

 

We are all UFH.

 

 

[SimonD]

I think you'll struggle to find a plumber who knows and understands manifold systems. You might just have to burn out your phone trying!

 

What you're proposing however is not impossible but the manifold manufacturers for cold and hot water distribution manifolds tend to suggest a limit to the number of ports. In some cases this is as low as 7 and in some it goes up to about 10. In my build, I needed 16 cold water ports and 11 hot water, so I built my own and feed the cold water manifold from the centre rather than the end - no problem so far with flow and pressure any where. Heating manifold wise I have one with 9 posts and 1 with 6 ports and all were a dream to balance.

 

I've yet to install a manifold system for a customer so @Nickfromwales is the man for long term experience in a variety of projects.

 

Here are mine (although a bit messy at the time as the water distribution manifolds were in experimental mode to see if they worked ok with the number of ports!).

 

 

[Kelvin]

I used the Rehau smart manifold system largely because it’s much more compact and lent itself to a neater install. I also felt it was a more robust system. This covers an island, a utility room, and two bathrooms. Each manifold has hot and cold that can be individually isolated  

 

Edited March 9 by Kelvin

[Nick Laslett]

Hello @SimonD, @JohnMo, what are your thoughts on the need for an inlet control group valve to balance the cold supply. 
 

https://www.unventedcomponentseurope.com/22mm-inlet-control-multibloc-valve-group-3-bar-6-bar.html/

 

In a lot of the threads about the manifold approach for distributing supply, there are lots of great pictures of the manifold, but not so much talk about inlet control group valve. Is this because it is a part of the UVC install?

 

I currently have my hot and cold manifolds, but have not got to the UVC bit as I will need to bring someone in for this. In my rental the UVC does not have an inlet control group valve and none of the thermostatic valves appear to work correctly, it is either hot or cold, there is no gradual change in the temp as I have experienced in the past. 
 

Does the inlet control group valve have any downsides?

[JohnMo]

Mine started with a combi boiler, same as the original poster. If starting from scratch with an unvented cylinder you really should take the cold water from the UVC inlet group as a balance supply.

 

If retrofitting as I did, I have a house inlet pressure control valve, as well as inlet control group on the UVC with the cold balance feed closed off. You also need a check valve on the UVC hot outlet to stop any reverse flow.

 

Ideally you would feed cold to the cylinder inlet group, and balanced cold water from inlet control group to the cold water manifold. Hot water direct from cylinder to manifold.

[sharpener]

1 hour ago, Nick Laslett said:

Does the inlet control group valve have any downsides?

 

Not really. It will have a filter screen in it which needs to be looked at occasionally but mine gets very little debris so once a year is enough. You need a balanced cold feed to all things like shower mixers. It is useful to have mains pressure at the kitchen sink and any outside taps so in practice it may be sufficient to pipe it to the upper floors. Unlike bath/basin fittings kitchen mixers do not actually mix within the tap body (Water Regs) so this is not a problem.

[Nick Laslett]

Thanks @JohnMo, I actually found your original thread about inlet control groups and balanced cold. 
 

Thanks @sharpener for the clarifications, where I was getting confused, is my cold manifold includes toilets, showers and basins. @PeterW covers this point where I was getting confused in this thread:

 

Quote

I feed WCs off the same branch as the outside taps but that is preference - they don’t need to have soft water or be reduced pressure.  

 

 

As I have already plumbed and tested my cold manifold, I’m not going to break it all apart. But the design nuance I missed, is that not all cold feeds need to be balanced like to a toilet cistern or kitchen tap.  

So for the benefit of others attempting to follow the plumbing manifold approach popular on BuildHub, you need to consider if you need a non-balanced cold manifold that comes before the inlet control group, this could also be hardwater if appropriate. All mixer outlets should/must* be fed from the balanced cold outlet on the control group. (*There are exceptions to this rule)

 

See Here:

 

[SimonD]

15 hours ago, Nick Laslett said:

Hello @SimonD, @JohnMo, what are your thoughts on the need for an inlet control group valve to balance the cold supply. 

 

1 hour ago, Nick Laslett said:

As I have already plumbed and tested my cold manifold, I’m not going to break it all apart. But the design nuance I missed, is that not all cold feeds need to be balanced like to a toilet cistern or kitchen tap.  

 

You've done your research well to dig out the older threads relevant to this question. I don't have a UVC but a Thermal store in my house - for multiple reasons it was the pragmatic choice at the time and still is as a dump for future excess of solar. So my feeds to the manifolds are not balance through a control group but simply balanced at a manifold that splits the supply to cylinder coil/cold manifold - pressure is reduced as needed at the rising main. On a UVC installation, I would just ensure, like others have said that all mixed outlets are supplied by the balanced supply through control group. In some retrofit installs it's just the only practical solution to feed everything through the control group due to existing plumbing.

[ZenMad]

Thanks everyone for the great input. I've asked 2 questions on this forum so far, and I've learned so much from everyone here already. So I tried to combine all my learnings, and put this together in a diagram. 

 

Here's what I'm doing:
- Use HWC + System Boiler instead of Combi Boiler

- Use Priority Domestic Hot Water set up

- Use PEX pipes for CH and DW water supply, but use copper for connections between boiler and HWC as I've read that with PDHW boiler can heat water up to 80 degrees for the HWC which is about the max PEX can take safely.

- Use multiple zones (1 for upstair radiators, 1 downstairs radiator, 1 of downstairs UFH) -- I want to split upstairs and downstairs as downstairs temperature should be lower than upstairs.

- Use manifolds for CH.

- Use manifolds for DW with an outlet for every wet room. In the wet room put another manifold where needed. Mostly doing this to save space in the boiler area. 

 

Just to call out once again that I have no plumbing experience what so ever, nor do even know if this is even possible or right! I just wanted to draw something out and get input from the professionals here before I'm sitting together with my heating engineer / plumber again to ensure the understand what I'm after.