Temperature Stability of PTC Heater

[Chance92]

There are PTC heaters out there designed to produce a constant temperature. I wonder if anyone has any experience with their stability? For example, if the environment temperature rises from 15C to 25C, how much will the heater temperature change?

[MK]

A lot depends upon the insulation you put around it.

[Birb]

Probably also depends on the steepness of the resistance-temperature curve? But too steep might result in oscillation

[EC8010]

If you need a reasonably constant (and adjustable) temperature, there are Chinese PID controllers. Five years ago, I bought two for £25. They were mains powered and included 10A solid state relay and Type K thermocouple. I grafted one into a tabletop oven to make a cheap temperature cabinet accurate to 2C (confirmed by separate measurement), stable to 1C. I later added a computer fan blowing downwards to stir the air up and keep temperature constant throughout the oven space.

SWMBO bought an air fryer yesterday. It uses a small induction motor to drive its fan and there looks to be enough room in the upper housing to fit a PID controller...

[Birb]

The problem is the pid controller is a bit bulky and may be a bit larger when an enclosed system is designed. Also, variable temperature may not be needed. I believe the original intention was to have it act as a an all in one solution for heating at a near constant temperature?