As part of my efforts to get the living room warm enough to actually be habitable over the winter I've done a quick heat-loss calculation and realised that the "professional" who did some work on the heating system a few years back undersized the rads so that the room only has around 60% of the heat going into it that it should have. That could explain a few things.
Anyway, a nice new rad turned up today to go under one of the windows to beef things up. The easiest way to plumb this in is to T off from the flow and return to a nearby rad. If I do this there will be a total of around 8.5kw all coming off one spur of 15mm pipes. Can 15mm pipes carry this much heat, I'm wondering? I could go back and T off from the main 22mm pipes, but frankly that will be a pain in the arse and require a lot of floorboard-lifting and joist-notching (not to mention extortionate copper-tube-buying) and I really don't want to.