Thanks for the education. My question shows how very little I know about pool pumps. I did learn a whole lot today though. Hayward has a nice PDF out there to help calculate pump size and AO Smith has a lot of good info as well.

The clean pressure of my filter is approximately 18 psi on high speed. Because the gauge we have on it goes to 60 psi I can't really say what clean pressure at low speed is, somewhere between 5 and 8 psi, I think. Next season I want to get a gauge that goes only to 30 psi so I can get better accuracy.

Anyway, we've decided to get a Pentair Dynamo 1HP Dual Speed - 11.0/2.9A 115V - model 340204.

The seller is PoolSupplyWorld.com. Have any of you ever dealt with them? If so, what has been your experience?