We always enjoy [FesZ’s] videos, and his latest about FREQ function in LTSpice is no exception. In fact, LTSpice doesn’t document it, but it is part of the underlying Spice system. So ...

A switch model already in LTSpice with built-in hysteresis takes the place of the thermostat. Using temperature data for a single day in January [Oxx] can see how each of his two heating systems ...