The UAA2016 from Motorola lends itself admirably to making a proportional mains-operated temperature control. A resistor with negative temperature control (NTC), R3, which must have a value of about 100 (12 at 25 °C, serves as a sensor. In the diagram, the heating element is a 100 W light bulb, which generates enough heat for a greenhouse or a climatic chamber (for testing electronic equipment). The triac can switch up to 3 A if it is fitted with a heat sink.
The properties of the regulator arc determined by the resistors at pins 1-4. Resistors R1 and R2 establish over -which range the temperature may be set to P1. With values shown, the range is 0-70 °C.
Closing S1 causes the temperature to drop by about 2 °C. The degree to which the temperature drops is determined by R4: a value of 100 K Ω results in a reduction of about 5°C.
Resistor R5 determines the hysteresis of the regulator: here, it is about 150 mV. How much that is in °C depends on the type of NTC and the temperature: an NTC has a non-linear temperature characteristic.
Do bear in mind that the entire circuit is connected to the mains and that, therefore, the regulators must be constructed with due care to safety regulations. It should be installed in a well-insulated, earthed if the metal case.