Radiator circuits with multiple push fit manifolds

[MoDo]

Would really appreciate some help with finessing my radiator plan before I start drilling holes… Hopefully some clarity here will help others in similar situations.

 

Heating will be provided by a heat pump supplied and installed by British Gas. However, they do not do first fix apparently, so that’s down to me. They have sized the radiators (almost all small type 11 – mostly 400mm or 500mm wide though the widest is 800mm). We have 10 in total including 3x towel rads. All radiators are for upstairs only.

We have UFH in the ground floor slab with a few spare ways in the manifold (installers decided to leave out a few circuits – but it is what it is). So, I could potentially run a few rads off the spare ways in the UFH manifold – not sure if that is a good idea or not?

I know many on here have used the UFH type manifolds with separate runs to each radiator. However, this isn't ideal as we have I-Joists and MVHR so I have to be careful to keep the necessary distance from existing holes drilled in the joists. Coupled with a number of impassable glulam beams, it isn’t really an option to run pipes from each individual radiator back to a central manifold. So as a compromise I’m planning on around 3 pairs of flow/return coming off separate push fit manifolds. I would locate each manifold in the area below the stairs (centrally located in the house - see blue/red rectangles on diagram) on the side closest to the rooms they are feeding. These would be linked with 22mm plastic and reduce to 15mm at the ports. (This central area under the stairs is where the heat pump primaries would enter the house and where the UVC will go.) I’d then run a maximum four radiators off each 15mm flow/return pair. ChatGPT has helped with calculating flow rates and losses over different lengths of pipe. It claims that by adding additional flow/return branches, flow rates will be improved – rather than running say all 10 rads off one 15mm flow return circuit – which of course makes sense. I’d tee off these flow/return pairs in the void between the joists or in the stud partitions for each radiator.

Does this sound reasonable?! Thank you.

 

Planned manifold type 2/3/4 port depending on how many flow/return feeds (pipe to be pert-al-pert 15mm):