I changed the fan to AUTO and expected silence between heating cycles. It kept starting periodically. Before assuming the thermostat was ignoring me, I looked for another setting that might be asking it to circulate air.
There it was: a minimum fan runtime per hour. The simple choice on the home screen had not told the whole story.
AUTO can include additional circulation
On supported ecobee controls, minimum fan runtime can operate alongside AUTO. ON requests continuous fan operation, while AUTO normally coordinates with heating and cooling calls plus any configured circulation.
Other thermostats use different names and options. The equipment may also run the fan briefly after a heating or cooling call. The model's instructions matter more than the assumption that AUTO always means completely off between cycles.
I recorded the original settings before making a change. I also checked whether a temporary hold was affecting the fan along with the temperature.
What do you want circulation to improve?
We wanted to know whether modest circulation helped the temperature difference between two occupied rooms. We tried the supported setting and watched the rooms under similar conditions.
Continuous fan use has operating costs and can affect comfort and humidity differently across systems. It is worth discussing the whole setup with the contractor, especially during cooling season, rather than assuming more fan time is always better.
A circulation setting also does not guarantee fresh outdoor air. That depends on the home's ventilation arrangement.
If the fan runs unexpectedly with every relevant control checked, or the system is not heating or cooling properly, that deserves service. A menu setting is only one possible explanation.
Our final choice was written beside the schedule. We knew what it was intended to do, which made it easier to judge whether it helped.
