Running your fan can cause higher humidity and mold

Many people have been told that changing your thermostat setting for fan from “AUTO” to “ON” will better distribute the cool air in your home. While this might technically be true, that’s not the whole story.

Just so we’re clear, an air conditioner has two components:
a) the part that cools, and
b) the part that moves the air.
You adjust the part the cools by changing the temperature setting on your thermostat. You adjust the air movement by setting the fan to “AUTO” or “ON.”

When the fan is in the “AUTO”┬ámode, the air conditioner moves air only when the cooling part is running. When the thermostat senses that the house has reached the set┬átemperature, it shuts off both the cooling and the fan. When the fan is in the “ON” mode, the fan keeps running continuously, even when the cooling part is turned off. While the cooling part is running, condensation builds up on the coils; the fan blows the air across these coils, pumping cool air into your home. However, when the cooling part is off, the fan simply blows that moisture straight into your home. This can lead to significant moisture build, especially in a place like Jacksonville.

The result of this is that the humidity in your home will increase dramatically when your fan is running and the unit is not cooling. This can cause your humidity levels to increase to the “sweet spot” for mold to start growing. Besides this, the cost for running your fan in the “ON” position will cost you significantly more, while not giving you much of a benefit.

At Hammond Heating and Air, we always counsel our clients to use the “AUTO” setting for the fan. We want you to keep cool, healthy, and as efficient as possible.

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