Warm days and cold nights call for thermostat settings for spring and fall that leave room between the heating and cooling setpoints. Auto heat/cool mode can switch between systems as needed; for background, see [thermostat basics](https://www.energy.gov/energysaver/thermostats) and [programmable thermostats](https://www.energy.gov/energysaver/programmable-thermostats).
Essential Concepts
Set heat below cool. Use Auto heat/cool, not Auto fan.