Evening, Currently I have an old Combi boiler system. I'd like to fit a new bathroom with a thermostatic shower. I have 7 rads, one bathroom. Question.. Is an unvented system more or less efficient than a good, new combi boiler. I have room to install a cylinder next to the boiler, in the cellar. I've also thought about having solar panels to heat the water. I know I need a cylinder for this.