This model simulates a thermostat - a device that responds to the temperature of a room in order to maintain the temperature at some desired level. The user can adjust the desired temperature, insulation of the room and strength of the heater to observe how the thermostat will perform under varying conditions. Thermostats are often used as examples of feedback control, where a system will adjust its behavior in response the effects of its prior behavior.
For detailed instructions on using the program, take a look at the info window from the Thermostat model.
Click on one of the pictures to see a quicktime movie of the model: