Higher energy costs
Since the fan is always running, you’re using more energy than when the fan only runs when your system is heating or cooling.
More frequent repairs
When set to ON, the fan runs more. This can increase wear and tear on your blower and lead to costly blower repairs.
Increases humidity
Your AC won’t dehumidify your home as well as it should, when the fan is set to ON.
Worsens air duct leakage
Most homes leak about 10% of the supply air and 12% of the return air through their duct system. So if the fan is blowing all the time, you’re always losing conditioned air thus running up energy bills.
Moral of the Story: Use the AUTO setting not ON.
More Ways to Save Energy
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