Hi Glyn, thanks for posting this spreadsheet. I note that the Sontex Superstatic 440 has the highest pressure drop of 0.6 M head at flow of 1.21 m3/h. I have a Sontex Superstatic 449 and if I have read the manual correctly, this has a staggering 1.45 M head pressure loss at 1.21 m3/h. This may partially explain why my flow rate for DHW is limited to 1.2 m3/h despite a 8 M head Grundfos pump. Have I got this right and should I be thinking about a different heat meter?
https://www.dmsltd.com/upload/pdfs/71aff5cf11d94e98b23c027a130ce161.pdf