Arrange the system so that the boilers output is combined with the heat
banks and a greater flowrate with a smaller cylinder

It is an indirect coil, so it won't have this ability. It needed to be
indirect, because I needed a pressurised sealed CH circuit, which obviously
isn't possible with a direct cylinder with atmospheric pressure water.

It is sized so I don't need to rely on recovery for it to work. The sizes
only affect the height of the cylinder, so there is no space implication in
going for a 180L instead of a 150L or a 120L. It's going in the loft.

Christian.