If putting a heating system in the system only has 23btus on it. But after picking up 3 rads. I have 3 more rads to pick up. That require 12000 btus of heat between them. Lounge a bedroom and the hall. I knew it says 15mm pipe will do 15,000 btus. But I am tempted to keep the run in 22mm till get to these rads which are all close together. And around 3 meter from were the over rads are. Any thoughts? Thanks