Adding single radiator to existing gas combi CH system

[GRC]

Boiler in garage, which is only 'room' on ground floor apart from entryway and stairs. Flow and return pipes disappear into brickwork next to boiler, with half a dozen rads at first floor, and five at second floor with two rad-style towel rails. No sign of a manifold anywhere. The radiator pipework is "microbore", if I have my terminology correct, with the visible pipework leaving the boiler in 10mm copper.

We want to get a heater in the entryway, which has none at the moment, and reasoned between ourselves that without access to the manifold, we could not do this (prev thread in electrics - https://www.diynot.com/diy/threads/...-for-oil-filled-radiator.623750/#post-5653793)

Is it a realistic possibility to take tees off the 10mm to hook up a rad directly off the flow and return adjacent to the boiler, or does it really need to be done at the manifold? Is there likely to be expansion capability at the manifold, with perhaps our dozen or so rads fitted to a 15-way or 20-way manifold?

Also, where would the manifold be, most likely, since it's not visible in any utility cupboard? Under floor? Between the cavity wall brickwork? Would it routinely be between the two floor levels which have the existing radiators?

 

[Madrab]

with the visible pipework leaving the boiler in 10mm copper

Should be 22mm for at least the first meter?

You can take a 10mm flow and return straight from the main backbone yes, just need to balance properly. If adding rads then that just needs to be considered as part of the whole system requirement and the capacity of the boiler of course. Don't go too large with the rad either.

Manifolds - If the system has taken proper design into consideration, they should be towards the centre of the property to make the runs to the rads as similar as possible. Coming back to the main pipework from the boiler, the 22mm backbone would normally run up to the manifolds to maximise flow.