Your Raypak heater has a minimum flow rate as shown in the chart below.
If you have no automation to increase the pump speed when the heater turns on then you need to run the pump fast enough so the required heater flow is always there.
If there is a time period when the heater does not run then you can schedule the pump to run at a lower speed.
The IF3 will give you the flow rate for a set RPM. So set your flow rate fast enough for your heater.
At times you know the heater will not run you can schedule the pump for 1200 - 1500 rpm to gently circulate the pool.
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