Your HVAC thermostat should have an “ON” mode and an “AUTO” mode setting. Florida homeowners should always use the AUTO mode. Following is an explanation for how the ON and AUTO settings work.

AUTO means the fan runs “automatically” ONLY when your system is operating and is the most energy efficient option for removing humidity from the air. The AUTO setting allows better dehumidification in your home. When you’re in the AUTO mode setting, moisture from the cooling coils is removed from the air and drained to the outside of your home via a drip line.

If left in the ON mode your fan runs continuously. When your AC is working properly the indoor coil becomes cold.  Water vapor from the air passing over the coil condenses; when the condenser shuts off the coil warms up.  In the meantime, the water on the coil will remain on the coil until the AC cycles again and a minimal amount of the water will evaporate back into the home.  When the fan mode is ON and the fan runs continuously the air passing over the coil warms up causing that water to evaporate more quickly putting that humidity back into the home.

Another issue with leaving the fan in the ON position is that when the desired room temperature is met the HVAC system stops running but the fan continues to operate, using more energy, resulting in higher energy costs.  More air flow means dirtier air filters, requiring more frequent changing of the filters.  And a continuously running fan puts more wear and tear on the system which may result in more frequent repairs.  Simply stated, leaving the fan in the ON mode will cost you more money and it will not remove the required amount of humidity to keep your home healthy.

The ideal relative humidity in your home should be maintained between 45% and 55%.  Anything above 55% puts your home at risk for developing mildew odors and microbial growth (mold).  This optimum range is best achieved by leaving your thermostat fan in the AUTO mode.

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