I am struggling to get my head around the calculation for kw output of an oil boiler by using nozzle size and pump pressure information. if anyone has info regarding the calculation formula or a chart or an app or something enabling a quick on site calculation I would be grateful. the riello and nuway helpline just reel them off and I am sure it is just about regular use means it is second nature just like when calculating gas kw but I thought I would ask if someone has devised a simple idiot type guide.