I want to swap some old rads for nice new ones. The old are from back in the '70s when the house was built so are all imperial. One is simple enough, it's 3' so I should be able to get a 900mm in (15mm difference which I'm sure I can get away with with the play in the pipes). The awkward one is 5' (1525mm). Looks like my best bet would be 1400. This gives me 125mm to find. Unfortunately I doubt if the water will jump from the valves to the rad so I was thinking of using two extension pieces to fill the gap, one each side obviously . Would Screwfix extension piece (cat no 4972R) do the job? Also the rads are on outside walls. Is it worth pasting the reflective foil/foam to the wall first to stop some heat escaping through the wall ?