What makes you think you need a 28kW or 30kW boiler?210l Santon Premier Plus Systemfit Indirect Unvented hot water cylinder and a Valiant ecoTec plus 630 system boiler.
The truth is I don't really know, I just wanted to make sure I got enough power. I always think it's better to look at it than look for it.
Let me give you some more info.
Full renovation of a mid terrace with 10' high ceilings. All ground floors have been lifted and insulated with celotex. Both front and back external walls have been insulated. There is 150mm of rockwool below all upstairs floors. Loft has been insulated with 125mm of clelotex. Biggest heatloss currently is the original sash windows. We plan to restore those and add secondary glazing before winter kicks in. There will be a full bathroom with power shower and 2 ensuites with power showers.