Should Your Thermostat Fan Be Set to AUTO or ON in Arizona?
The temperature outside may still feel like summer in September, but Arizona homes begin spending more time between long cooling cycles. That is when homeowners often notice the other switch on the thermostat: FAN AUTO or ON.
The two settings do very different jobs. Understanding them can help you avoid unnecessary blower operation and may also reveal an airflow problem that has been hidden during peak summer.
What AUTO Actually Does
With the fan set to AUTO, the indoor blower normally runs when the heating or cooling system is operating. When the thermostat finishes the heating or cooling call, the fan shuts off according to the system’s normal controls.
That is the standard operating mode on many residential thermostats. Resideo, which manufactures Honeywell Home controls, describes AUTO as running the fan with the heating or cooling system, while ON keeps the fan operating continuously.
For many Arizona homes, AUTO is a sensible everyday setting because the blower does not have to run around the clock simply to move untreated air through the ducts.
What Happens When You Select ON
ON tells the blower to continue circulating air even when the air conditioner or furnace is not actively cooling or heating.
That can sometimes make temperatures feel more even between rooms. It can also increase the amount of air passing through the filter. A homeowner may therefore use continuous fan operation temporarily when trying to reduce stagnant air in a particular part of the house.
The tradeoff is that the blower consumes electricity while it operates. It also does not correct the underlying reason one room is uncomfortable. If continuous circulation is the only way to make a bedroom tolerable, the duct layout, return path, insulation or airflow balance may deserve inspection.
Some Thermostats Offer CIRCULATE
Newer thermostats may provide a third option called CIRC, CIRCULATE or a programmable fan schedule. Instead of running continuously, the thermostat operates the blower for part of each hour.
For example, some Resideo thermostats use a circulate mode that runs the fan periodically rather than all day. Smart thermostat systems may also allow fan operation to be programmed by comfort setting.
This can be useful when a homeowner wants occasional air movement between cooling cycles without choosing continuous operation.
Do Not Confuse Fan AUTO With System AUTO
There may be two different AUTO settings on the thermostat.
Fan AUTO controls the indoor blower. System AUTO allows the thermostat to choose between heating and cooling when indoor temperature moves outside the programmed range.
That difference matters during Arizona transition months. A thermostat can have the system set to COOL while the fan remains on AUTO, or the system can be on automatic changeover while the fan is independently set to ON.
Check the display carefully before assuming that AUTO refers to the entire HVAC system.
Constant Fan Use Can Hide Another Problem
If one part of the house becomes uncomfortable whenever the blower shuts off, lowering the thermostat or running the fan continuously may only mask the issue.
Tru Comfort already notes that loose, damaged or poorly insulated ductwork can contribute to uneven room temperatures. The United States Department of Energy likewise advises homeowners to check for crushed or disconnected ducts when conditioned air is not reaching the intended room.
A technician can compare airflow, inspect accessible ducts and determine whether the problem lies with the equipment or the distribution system.
Check the Filter Before Changing Settings
Any fan setting depends on free airflow through the system. A dirty filter increases resistance and can reduce the amount of air reaching the rooms.
Follow the filter manufacturer’s replacement instructions and check it more frequently during dusty periods. Do not substitute a highly restrictive filter simply because it looks more substantial. The equipment and duct system must be able to handle the filter being used.
Get the Thermostat and Airflow Working Together
Tru Comfort Heating and Cooling provides HVAC diagnostics, thermostat checks, air conditioning service and air duct solutions for homeowners in New River, Anthem, Phoenix and nearby communities. If your system only feels comfortable with the fan running constantly, call 602 499 7855. Tru Comfort’s NATE certified, noncommissioned technicians can inspect the airflow and controls and explain what the system actually needs.
Live References
Tru Comfort Heating and Cooling
Resideo T6 Pro Thermostat Fan Modes
United States Department of Energy Consumer Guide to Home Heating and Cooling