DHW/CW Manifold location & configuration

[SelfBuildSmurf]

Evening all,

I'm trying to finalise a plan for re-plumbing our renovation but excessive procrastination on my part has me here seeking guidance from BuildHub members,

In short, we are renovating the entire house which necessitates a re-plumb and re-wire,

We are moving from gas fired Warm Air Heating (Brink B-23D) and Immersion hot water to an ASHP with Unvented Cylinder (finally hot water at decent pressure!).

We have a HeatGeek proposal from a local installer, but I have decided to take on the UFH downstairs and UFH overlay upstairs to reduce the quote, and owing to build timescales I have run a length of pre-insulated pipe below ground from the proposed heat pump location to the utility room shown on the drawings (approx 20m).

 

House heat loss has been calculated at 13.42 kW and the design done to -3.0 C (Cambs)

- Vaillant aroTHERM plus 12Kw Heat Pump

- Vaillant uniSTOR 300L HWC

 

We would like to install a Water Softener too, as we are in a hard water area.

 

I had initially intended to put the UVC and plumbing manifolds in the plant room but it would result in a pipe run from plant room to the kitchen sink of approx. 22m which strikes me as being less than ideal.

As the insulated pipe for the ASHP comes up in the utility room, I am now considering putting the UVC in there as well as the plumbing manifolds, I am yet to run a new 32mm mdpe mains supply, which will be either into the utility or plant room once I've bitten the bullet!

 

I've come up with the following manifold configuration for outlets,

Redacted Drawings.pdf

 

Being more familiar with a branch and tee system, could I ask your opinion please on the proposed manifold configurations for DHW and CW please?

- Given the length of the runs would you instead opt for one run to each room and split within i.e. a 22mm run to a manifold in the bathroom and then 15mm feed to each outlet?

- Is there a general rule of thumb on pipe size to certain outlets? (i.e. 22mm to bath, 15mm to sink etc....)

- Any other general pointers?

 

I've attached the floor plan below

[JohnMo]

I just have 15mm from UVC to manifold and then 15mm for each wet room, then branch from there.

 

Flow is more adequate. Wouldn't do 22mm for any hot water, you will waiting too long for hot to come out of the tap.

 

Did similar for cold water.

[SelfBuildSmurf]

Thanks @JohnMo,

Are your manifolds serving multiple showers as well? Do you notice any drop in water pressure etc. or noise issues if two showers are in use?

Edited yesterday at 07:22 by SelfBuildSmurf

[JohnMo]

Flow rate goes down with multiple showers on at same time, but you are only delivering what the water main will flow at a max anyway. Two showers is fine, 3 usable but unlikely 3 people would shower at same time. Never noticed any noise ever.

[SimonD]

On 05/09/2025 at 09:53, SelfBuildSmurf said:

Evening all,

I'm trying to finalise a plan for re-plumbing our renovation but excessive procrastination on my part has me here seeking guidance from BuildHub members,

In short, we are renovating the entire house which necessitates a re-plumb and re-wire,

We are moving from gas fired Warm Air Heating (Brink B-23D) and Immersion hot water to an ASHP with Unvented Cylinder (finally hot water at decent pressure!).

We have a HeatGeek proposal from a local installer, but I have decided to take on the UFH downstairs and UFH overlay upstairs to reduce the quote, and owing to build timescales I have run a length of pre-insulated pipe below ground from the proposed heat pump location to the utility room shown on the drawings (approx 20m).

 

House heat loss has been calculated at 13.42 kW and the design done to -3.0 C (Cambs)

- Vaillant aroTHERM plus 12Kw Heat Pump

- Vaillant uniSTOR 300L HWC

 

We would like to install a Water Softener too, as we are in a hard water area.

 

I had initially intended to put the UVC and plumbing manifolds in the plant room but it would result in a pipe run from plant room to the kitchen sink of approx. 22m which strikes me as being less than ideal.

As the insulated pipe for the ASHP comes up in the utility room, I am now considering putting the UVC in there as well as the plumbing manifolds, I am yet to run a new 32mm mdpe mains supply, which will be either into the utility or plant room once I've bitten the bullet!

 

I've come up with the following manifold configuration for outlets,

Redacted Drawings.pdf 322.55 kB · 5 downloads

 

Being more familiar with a branch and tee system, could I ask your opinion please on the proposed manifold configurations for DHW and CW please?

- Given the length of the runs would you instead opt for one run to each room and split within i.e. a 22mm run to a manifold in the bathroom and then 15mm feed to each outlet?

- Is there a general rule of thumb on pipe size to certain outlets? (i.e. 22mm to bath, 15mm to sink etc....)

- Any other general pointers?

 

I've attached the floor plan below

 

I have distribution manifolds as central to the house as possible and from these manifolds I run individual pipes to each outlet. This means I can run small 10mm pipe to basins/wcs ect. and 15mm to showers etc. For maintenance it works great as each outlet can be isolated but the rest of the room can be used - e.g. servicing the basin taps while still being able to have a shower and now of those terrible isolation valves that always leaks after a few years.

 

You really don't need 15mm to go to sinks/wc flush etc. and with decent pressure you don't need 22mm to go to a bath either. We have a couple of long runs and as I've used 10mm pipe, the hot water is there very quickly. If you run 22mm to a bathroom and then split from there, every time you need hot water you have to draw a lot of volume to purge to pipe of cold before you get hot.

 

[SelfBuildSmurf]

Thanks again for the insight @JohnMo,

 

I understand what you mean @SimonD, as a compromise I've seen some run from central manifold in 15mm to a manifold in the bathroom and then split to outlets. With en-suites typically used morning/evening in conjunction with a shower I guess it reduces the time waiting for HW to arrive. I can see from the forum that Hep2o manifolds are well recommended I've seen repeated reminders by @Nickfromwales and others to ensure any garden taps are not connected to the DW manifolds. So I'll start sourcing those material in due course,

 

I'm now back to weighing up whether I do have to sacrifice part of the utility room for ASHP performance and efficiency (i.e. locate the UVC in there and associated plumbing/manifolds) or whether the ASHP could still perform efficiently if I extended the flow and return to the plant room. But looking at the specification tables it appears just the now installed subterranean flow and return (22m pre-insulated pipes with ID of 42mm) may be a little over ambitious.......

 

I'm now thinking a run similar to that outlined below (approx 30m ish) would definitely be a little too ambitious!

As a side note, it's today that I really wish I had concentrated and finished my M&E apprenticeship all those years ago.

 

 

 

[SelfBuildSmurf]

Also, if I may. I'll be running a new 32mm MDPE main along the same trench and I see Plasson couplings are well thought of on the forum.

I will be using at least two tee's to split the new mains feed, one x 'front garden tap', 1 x 'house supply' and 1 x 90 for a 'Rear garden tap'. Would you try to keep the fittings accessible or are they genuinely a fit and forget product? Is there a preference between push-fit / compression? If accessible any recommendations on how? Thanks

[crispy_wafer]

I did similar, kept accessible, because I’ve put stop taps on the two feeds off the main.  Saves me having to go out to the road to kill the individual tails.  I’m in the process(2 years, because not important just yet) of building up a chamber, it’ll be something along the lines of 700*1250 ish so I can get into it should I ever need to.  There’s probably a better way, maybe theres a manifold for mdpe which could simplify matters, haven’t looked tbh.

[SelfBuildSmurf]

Thanks @crispy_wafer, I was looking at the plastic duct chambers and perhaps doing the joints in those, while it means they are accessible they would then have to be a decent size to allow bending the mdpe back out of a connection and in again if they ever needed to be changed,

 

And if they're unlikely to ever need changing, then why bother with the access chamber,

 

Another example of the procrastinating I'm doing!