I am a diy'er replacing my pressure tank. I understand from the research that I have been doing that the pressure tank should be sized so the pump runs for at least 1 min for up to 3/4 hp, 2 min for 1 to 2 hp, etc. I do not know the hp of my pump. How can I determine this? I know that the pump puts out about 10 gpm (based upon drawdown on the current tank) and is powered by a 15 amp 240 volt circuit. How crucial is it to determine hp rating of pump? Can I go with an average of 1.5 minutes for minimum runtime?