A pool heater (258) with a fin and tube heat exchanger (210), includes fins (216) shaped along dynamically, empirically determined isothermal lines. The fins (216) preferably have deflectors (248) along a trailing edge thereof to concentrate heat flux into a back row of tubes (212). The deflectors (218) bridge adjacent fins (216) to define baffles. The preferred fin (216) shape may be obtained empirically by trimming fin areas exhibiting excessive temperatures during operation.
