I have a question regarding something I read on the website for my gas pool heater. The website states "The Pool Sizing Guide shows the maximum pool surface area our Legacy models will heat based on the temperature difference between the air
temperature during the coldest month the pool is used and the desired pool temperature. ".
This weekend our temp is rising to the mid 70s. We're contemplating firing up the heater and I was wondering why the heater sizing guide works off of the difference between air temperature and desired water temperature instead of the difference between actual water temperature and desired temperature.
Lets say air temp is 70F and I want water at 85F (15 degree difference) but actual water temp is 50F (35 degree difference). Why does is the heater sizing guide based on air temp instead of actual water temp? I apologize if its a dumb question...