When I first started in the pool business in 1976 most pools had 1/2 horse power or 3/4 hp pumps. Today most pools have a 1-1/2 hp or 2 hp pumps. Arrr Arrr Arr as Tim Taylor says, but is a larger hp pool pump always better? The pump manufacturer can manipulate the pump horse power by changing the service factor rating of the motor. You can actually have the exact same motor on a 1-1/2 hp pump as on a 2 hp pump.
Pool pumps should really be rated by the gallons per minute of water flow instead of the motor’s hp. You need a pump that will be able to pump all the water in the pool through the filter in 8-10 hours. Which is 40 gpm for smaller pools and 80 gpm for larger pools. When replacing a pool pump you should check the flow rate of the existing pool filter. The gpm of the pump will go down the farther away from the pool the pump is located. Valves and PVC turns will also restricts the pumps gpm.
Today in our green energy efficient world it is even more valuable to get the most gallons per minute from your pool pump with the least horse power motor. Increasing the PVC pipe size from 1-1/2″ to 2″ will increase any pumps gpm. Other options to make your pool pump more efficient include a pump timer, 2-speed motor and the newer variable speed pumps.