I doubt you would get enough money in reduced costs for the pool pump by dropping to a 3/4 HP. I suggest waiting till the motor dies and then changing the seal set and impeller too.

The booster needs to be a 3/4 for the amount of pressure it creates, not for the volume of water it moves.

Scott

Thanks for the quick response and cost-saving suggestion. I'll wait until the present pump or motor dies before considering replacement. However, when that time comes, would a 2-speed be cheaper to run than a single speed?

garyduse...yes, a 2 speed will offer considerable savings over a 1 speed.

When operating at low speed, the power draw goes down exponentially with speed.

Examples, a typical 2 HP 2 speed pump uses .33 HP at low speed which is half speed.

A 1.5 HP 2 speed pump uses about .25 HP at half speed.

A .75 HP 2 speed pump uses about .1 HP at half speed.

Running the pump for longer periods of time during the day will save significant power and lower your monthly energy bill accordingly.

The return on investment will be quick as a 2 speed replacement motor is not much more than a 1 speed. The return on investment will depend on your electricity rate.

That being said, when you convert to a 2 speed, you will also have to get a timer or pool control system that will switch the pump from low speed to high speed when needed.

Hope this helps.

trhought--
Thanks for the input.
After trying to digest all the various constraints on pump sizing (line size, pool turnover, filter size, etc.), I'm coming around to thinking that:
1) It would be better to size the pump for 1 turnover in 24 hours. In my case (32000 gal) this would mean a minimum flowrate of 22 gpm.
2) The objective of a higher flowrate would be to occasionally stir up the pool water and perhaps improve filtration (my American Products High Rate Sand Filter manual says that it is designed to operate "at flow rates of from 15 to 25 gpm per sq ft of filter area". In my case (24" dia), this would mean a flowrate of 47 to 78 gpm).

If this is correct, it would seem that a 2-speed pump that would provide this range of flowrates would be ideal. I could run the pump for, say, 22 hours on low flow and then a couple on high flow.

Are there pumps out there that would work for me in this way?

garyduse...a 2 speed 1HP at high speed will provide about the same flow as your existing 1HP pump.

When the speed is cut in half, the flow is also cut in half, so you should expect about 25 gpm or so at low speed.

Hope this helps.

trhought----
Thanks. That's probably the way I'll go when I go for a replacement.