Question: I want to use an attic temperature switch that can turn the power to the PCS3 on and off when the attic reaches the set temperature. Is this possible?

Yes, it should be a switch that turns on when the attic temperature rises and turns off when it goes down below your set point. You can wire the 115 vac hot side to the switch terminals. The PCS3 only uses 4.5 amps max and standard attic switches usually handle that amount of current.

In order for this semi-automated operation to succeed, the pool pump must be running. Otherwise, the attic will be vented and no heat transfer will take place.

A good strategy would be to set the pool pump to run during 11 am to 9 pm. The operating logic would then be: During this period of time, the attic pool heater will turn on when the attic reaches the set point. The temperature you set.

Most switches are mechanical in nature and have wide tolerances such as + or - 5-10 degrees. Keep this in mind when your create your set point.