I have a concrete floor downstairs, so my plumbers took the hot feed into the utility room from the garage-wall-mounted boiler, into the ceiling-space;-- pump out in the garage, and diverter valve in the flat-roofed utility-room. A small radiator was teed-off prior to the 22 mm feeds going thro' into the main house, below the upstairs floor-boards, where they end at manifolds. Smaller-bore pipes take hot feed from one manifold to all the radiators, unseen mostly, making use of the hollow stud-partition plaster-board walls, and the returns come back via the other multi-branch manifold. Unfortunately, 10 years ago, when my installation was done, plastic plumbing did not have the respect in the industry as copper enjoys. I have indeed had brown sludge problems, clogging downstairs radiators. I am informed that the pipes in my house can breath air in thro' the wall of the pipe, even without leaking water out. Plumber firms in my area are ripping out these old pipes and pulling thro' "hep2o" piping, made by a firm called "Hepworth", and currently quotes a 50 year guarantee. It is double-wall barrier-pipe, and comes in 10 mm, 15 mm, 22 mm, and 28 mm, with the choice of push-fit plastic/rubber finger-tight couplings, or copper compression couplings, with a reinforcing sleeve of copper bracing the o-ring zone from inside. I have an example of re-piping costs being about Â£1000. Most plumbers in the UK still would only fit copper in their own homes. The USA is shifting faster towards the modern material.