Hi guys, I am first fixing a new central heating system in my house, I have run 22mm plastic around the ceiling void which tees down to 15mm pipe for the rads. The pipes feeding the downstairs are chased into the exterior walls but aren't ideal as they don't flex enough to make radiator connection easy. I asked a plumber to look at it and he said they shouldn't be in exterior walls due to heat loss. The ground floor is concrete floors. A new gas main needs to be installed, can this be buried in concrete floor? Can I fit 15mm to 10mm reducers to radiator feeds and run more flexible 10mm pipe to boxes behind rads? Any advice welcome.