Get up to $2000 tax credit on select AC systems! Call now to learn more.

Get up to $2000 tax credit on select AC systems! Call now to learn more.

Get up to $2000 tax credit on select AC systems! Call now to learn more.

Hate Humidity? Don’t Set Your Thermostat Like This

In Florida, we know and dread the thick blanket of warm air that hits us when we open our front door.

And we also know that humidity should NOT be something we feel in our own homes.

But you might be inviting humidity into your home without even knowing it.


By setting your AC thermostat fan to ON instead of AUTO.

Let’s take a closer look so that you know how and why to avoid this common mistake.

On vs AUTO: What’s the difference?

ON and AUTO are the two settings for your AC fan.

The difference between ON and AUTO boils down to when the fan blows:

  • In the AUTO position the fan only blows during an AC cooling cycle.
  • In the ON position the fan blows constantly, even when the AC isn’t cooling (which also means it uses more energy and costs more).

So, what does that have to do with humidity?

To better understand how a fan affects indoor humidity, let’s first look at what the AC fan does and where it’s located.

If you have a split system AC, you actually have two fans in your AC unit: one fan for your outdoor unit and one fan for your indoor unit.

But for the sake of this article, we’ll only be looking at the fan on the indoor unit (we’ve pointed it out in the picture above).

Your fan sits directly behind the cooling coils and is responsible for pushing air through the ducts and into your home.

So, what does the ON setting have to do with humidity?

Basically, the ON setting is not allowing your AC to properly dehumidify your home.

That’s right, your AC actually has 2 jobs:

  • To cool your home and
  • To dehumidify your home

Here’s how your AC normally dehumidifies your home: When warm air from inside your home is pulled into your indoor unit, it passes over very cold refrigerant coils.

Those cooling coils absorb the warmth and moisture from the air. Then that cold, dry air is pushed back into your home.

What happens to the moisture? Where does it go?

Well that completely depends on the setting of your fan:

If the fan is set to AUTO, that moisture collects and sits on the refrigerant coils. And once the fan shuts off in between cooling cycles, that moisture has time to slide off the coils and drain away outdoors.

But if the fan is set to ON, the moisture on the refrigerant coils does not get the chance to drain away. Because the fan blows constantly, most of the moistures evaporates and gets blown right back into your house!

So, quick recap:

  • The AUTO setting lets your AC properly dehumidify your home by stripping the air of moisture and pushing that moisture outdoors.
  • The ON setting prevents your AC from properly dehumidifying your home because the moisture that is stripped from your air is eventually pushed right back into your house.

So, what’s the purpose of the ON setting?

Yes, the ON setting should never be used if you want to prevent high indoor humidity.

But there are still some situations in which the ON setting comes in handy.

Here are a few ways the ON setting can be helpful:

  • It improves your air quality. Because the fan runs constantly, air is constantly being pulled into your air handler through the AC filter. This means much cleaner air, especially when you invest in advanced air cleaners.
  • It helps you keep your home cleaner. When you’re dusting or vacuuming, you’re kicking up a lot of dust. Keeping your AC fan on while you’re doing this helps suck up the dust before it settles back into the carpet or other surfaces. Related: “Thermostat Hack: When Vacuuming, Turn Your Thermostat to This Setting”

Need help from a professional AC contractor?

Cool Today serves customers across Florida and has locations in Tampa, Dunedin, Orlando, Sarasota, & Naples.

Posted in: Tips

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