I want to add a radiator to my system. Looking at other posts I think I have a 1 pipe system (combi) all inputs Therm valve sides connected to one pipe (flow) and other side to another (return)? does this sound right.Can I just 't' off from these pipes, through floor through 4" wall to new rad. I will put a 22mm copper tube in hole first for 15mm to sit through. Obviously drain down first.Just really appreciate a nod from the experts here.