heat energy source

[CyberWizard2261]

I'm trying to make a "salt evaporation pond" powered by my heat solar panels and for this, I used a furnace with heat energy source and it works! As soon as the temperature rises above 15C it starts working.

Problem: I wanted it to start working at 40C, does anyone know if heat energy source has any kind of "target temperature" like boilers?

Thanks in advance