Thanks for the great input. Since I have a seperate pump for the spa and no solar I’m going with a two speed pump. Slow in the winter and high during high use summer. On slow mode it should flow at just above the rate needed for the heater.

If I were to consider adding a solar, I would get the Intellaflow as you can dial down the rpms lower than a two speed. Ok for solar but not for a gas heater which needs a higher flow rate.

After I get it in I’m looking at constructing a simple controller/timer that will run the pump at high speed during the peak use times and slow the rest.

I do like that the water is being circulated rather than shutting off the pumps completely. Algae can be a pesky nuisance.