How to map PID output to actuator control? I'm building a control system for the heating of a house. A sensor reads the temperature inside and is then used as the input in the PID control. The temperature is then controlled by a servo which opens and closes a shunt were water runs to the radiators. I understand all the inner workings of the PID library for Arduino and PID in general, but the thing I don't understand is what I'm exactly supposed to do with the output signal I receive. In what way should the output signal correspond to how open or closed the shunt is?

I understand I can simply map the output signal to the servo signal, but is this the correct way? And with what angle coefficient should I map it with, cause that is basically set with the P parameter, isn't it? Is there some standard way to map the output signal to the actuator "signal", so that that tuning parameters are somewhat "standard". 

Hope someone understands anything of what I tried to explain :)
I don't think you would need to use a PID library (or any control loop for that matter) to control a radiator. You could use a simple threshold code, like this:

Pseudocode:

Check temperature
If radiator is off and temperature &gt; (ideal temp - threshold)
  turn radiator on
If radiator is on and temperature &gt; (ideal temp + threshold)
  turn radiator off