I'm planning a new CH installation and I have one ground floor room that has a solid floor, and all its walls are traditional brick & plaster. I don't want to run surface mounted pipes to the radiator if I can help it, but I was wondering whether I could fit a radiator on an internal wall, back to back with another in the adjacent room (suspended timber floor). If I put a tee in the pipes rising from under the floor to the radiator valves, could I pass a short length of pipe horizontally through the wall, and then fit an elbow to bring the pipes up to the second radiator? The combined capacity of both radiators is 2.3kW and I'm using 15mm pipes to the individual radiators from 22mm main pipework.