What the fan "Circulate" setting does
Circulate runs the blower fan for part of every hour even when nothing is heating or cooling, to keep air moving through the house. It sits between Auto and On. Brands differ on how much the fan runs and on whether heating and cooling time counts toward that share, so the same name can mean different amounts of fan time.
What does Circulate actually do?
It gives the blower a minimum share of each hour. With the fan on Auto, air only moves while the system is heating or cooling, so on a mild day the ducts can sit still for hours. With the fan on On, it never stops. Circulate is the middle ground: the thermostat starts the fan on its own for part of every hour, then lets it rest.
Sensi describes the purpose plainly: the feature lets the fan circulate air when the system is not running. Nothing is heated or cooled during those extra minutes. The fan only moves the air that is already in the house through the ducts and the filter. If you are deciding between the three choices, the side-by-side on fan "On" vs "Auto" lists the share each model uses.
Does heating and cooling time count toward the circulate share?
This is where brands part ways, and it changes how much extra fan time you get.
Sensi counts it. Its support page gives a worked example: set the circulating fan to 50% and the target is 30 minutes in the hour. If the furnace runs for 15 minutes during that hour, the fan only runs on its own for the other 15 minutes, at the end of the hour. On a hot or cold day, when the system is already running a lot, Circulate adds little.
Honeywell's VisionPRO TH8000 does the opposite. Its manual says Circ runs the fan "randomly, about 35% of the time, not counting any run time with the heating or cooling system." Heating and cooling time comes on top of the circulate time, not out of it.
The T6 Pro manual only says Circ runs the fan "randomly about 33% of the time," and Honeywell's T5, T5+ and T6 Pro Wi-Fi page says Circulate runs it 30% of the time every hour. Neither says whether heating or cooling runtime counts.
How do the brands set and show it?
| Thermostat | Where you set it | What the screen shows |
|---|---|---|
| Honeywell Home T6 Pro | Fan button, cycle to Circ | Fan mode Circ |
| Honeywell Home VisionPRO TH8000 | FAN key, choose Circ, press DONE; can also be set per schedule period | Circ, or Auto and Circ together when the schedule calls for it |
| Emerson Sensi smart thermostat | Menu, Next to "Fn Setup", up arrow to pick a percentage | "FAN" where the time or humidity usually appears |
| Emerson Sensi Touch | Menu, Advanced Set Up, Fan Mode Options, Circulating Fan | "Fan Circulate" in the fan mode area |
| Emerson Sensi Touch 2 | Mode icon, Fan Control options, Circulate Fan, then + and minus | Not stated |
| Emerson Sensi Lite | Hold Menu about 4 seconds, then the down arrow past "Au" and "On" | Not stated |
| ecobee (fan minimum runtime) | Varies by model; in the app, Menu, System, Fan | Not stated |
| Google Nest (fan schedule) | Google Home app: Settings, Schedules, Fan | A fan icon while the schedule runs the fan |
On a Sensi, the setting goes in 5% steps. Sensi's manual for the Sensi smart thermostat lists it as "Fn", off by default, with options from 10% to 100%. At the Sensi Lite thermostat the range is 10% to 95%, and Sensi describes that model's fan as running "after each HVAC cycle."
On a Nest, the fan schedule works in minutes, not percentages. You pick a daily window with "From" and "To" and then 15, 30, 45 or 60 minutes per hour within it. Google notes that on the Nest Learning Thermostat (3rd gen) and Nest Thermostat E, the same fan schedule applies to every day.
On an ecobee, the equivalent is the fan minimum runtime, in minutes per hour. ecobee says a runtime over 5 minutes is split evenly across the hour, and that if a hold is active you have to cancel it before a new runtime value takes effect.
Does every thermostat have Circulate?
No. Nest and ecobee have no setting called Circulate; their fan schedule and fan minimum runtime do the same job under other names. On a Nest, the fan can only run by itself if a wire is connected to the thermostat's G terminal. Without one, Google says fan options do not appear at all. The Honeywell T4 Pro offers only Auto and On.
How is Circulate different from running the fan after a cycle?
Circulate is about the whole hour. A few thermostats also have a narrower setting that keeps the fan going for a short time after heating or cooling stops:
- ecobee. "Heat Dissipation Time" and "Cool Dissipation Time" in the Thresholds menu adjust the fan runtime after a heating or cooling cycle, to circulate the remaining heated or cooled air.
- Honeywell Home T6 Pro Smart. Installer options 390 and 391 keep the fan on after a cooling or heating call ends, for 30, 60 or 90 seconds or 2 to 15 minutes. Both are off from the factory. For cooling, Honeywell warns it "may reintroduce humidity into the living space."
When does Circulate make sense?
When rooms feel uneven or stuffy between cycles and you do not want the fan running all the time. Google says longer fan use may help even out temperatures between rooms, but it also says the fan can use a lot of energy and that the extra runtime may mean replacing the air filter sooner. A part-time setting keeps some of the benefit with fewer fan hours than On.
If the fan now seems to run when you did not expect it, including with the system off, see fan runs when the system is off and Off mode.
Frequently asked questions
- Does Circulate run the fan at random times?
- On some Honeywell Home models, yes. The T6 Pro and VisionPRO TH8000 manuals both say the fan runs randomly for its share of the time. ecobee instead spreads a runtime over 5 minutes evenly across the hour, and Sensi says that when heating or cooling has run, the remaining fan time comes at the end of the hour.
- Why does my thermostat show Auto and Circ at the same time?
- On a Honeywell VisionPRO TH8000 that is normal. Honeywell says Auto means the thermostat is following a programmed fan setting, and Auto with Circ means the schedule calls for Circ during the current period.
- Will Circulate run when the thermostat is off?
- It depends on the brand. ecobee says its fan minimum runtime runs regardless of the System Mode, while a Nest fan schedule will not start while the thermostat is set to Off. The Honeywell and Sensi pages cited here do not say either way.
- Is there a setting that runs the fan only after a cycle ends?
- Some thermostats have one. On ecobee it is Heat Dissipation Time and Cool Dissipation Time, in the Thresholds menu. On the Honeywell Home T6 Pro Smart it is installer options 390 and 391, which are off from the factory.