I've read various threads and views and back and forth and done some calculations based on information I have found here and of course from the very helpful spreadsheets provided by our friend @Jeremy Harris.  I had pretty much decided ages ago I would get an 8.5kW Ecodan, which might go up to an 11.2kW ecodan unit.  However I have not really advanced it beyond basic assumptions, what others done and some quick back of the fag packet calcs. I'm about to start foundations shortly hence, need to f