Designing a central heating system is not a simple task, and requires a reasonable amount of knowledge. However for a domestic installation, there are many books available which will point you in the right direction. In very general terms, microbore is easier to install, as it is fairly flexible. 15 or 22 mm copper is not flexible, however it can be bent using springs or a tube bender. On the down side, microbore is far more susceptible to blockages from sediment in the system, and may be noiser as pumps need to work harder to overcome the additional pressure drop in microbore pipe. Higher fluid velocity also contributes to noise. I know many installers who would not touch microbore, but it is down to personal preference. In both cases, a well designed system, properly installed, should give years of reliable service.
