Thanks to a dripping manifold which has spurred me into action, I am finally getting around to replacing my 8mm microbore with some decent sized copper pipe. The manifold is fed by 22mm both flow and return and I was planning on teeing into the flow with more 22mm up the hall towards the radiators (about 3m away) before reducing to 15mm. Will I need to return the same distance with 22mm or will 15mm back to the 22mm be ok?