Got an old system with a few weeping 10mm joints and a real mismash of 10, 15 and 22mm pipe. I have access to all the pipework due to renovating house and plan to renew the rads and pipework (plastic sorry). Lounge is a 4.5 x 4.5 x 2.5 high with a stone exterior wall. Online calculators give 1.5Kw so I've upped this to 2Kw to allow cooler output from the boiler. As I've got the chance now would two spaced apart smaller rads be a better solution than one large.