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AUTO vs. ON: Choosing the Best Setting

Thermostat Settings - AUTO vs ON

What you don’t know about your air conditioner might be costing you. Especially when it comes to choosing between your thermostat’s AUTO and ON settings. Making an informed decision about these settings will impact your comfort and electric bill.

AUTO and ON Defined

Let’s start with the basics. All single-stage air conditioning systems come with two major operation modes – AUTO and ON. (“Single-stage” means that the air conditioner runs at all or nothing. Either it is cooling or heating your space at full blast, or it is off.)

Every air conditioner is equipped with a blower, or fan, which is a motorized part that circulates the heated or cooled air throughout your space. When your air conditioner is set to AUTO, both the compressor (the part that cools / heats the air) and the fan (the part that moves the conditioned air) cycle on and off simultaneously when the temperature reaches the thermostat’s set point. When your air conditioner is set to ON, the fan runs continuously, even when the cooling / heating cycle is off.

Now that we’ve covered the nuts and bolts, let’s move on to the pros and cons of AUTO and ON. First, let’s look at energy efficiency.


AUTO is More Energy Efficient

The ON setting, because the fan is constantly running, uses more electricity than AUTO. One FPL (Florida Power & Light) Expert estimates in an example of a home where the air conditioner cycles off 30% of the time, using the ON setting would cause the fan to run 200 hours longer per month. This would cost the theoretical homeowner $8 more per month.

AUTO Offers Better Humidity Control

Humidity control is an important function for air conditioners in the Sarasota and Charlotte county area climate. The AUTO and ON settings influence how effectively your air conditioner dehumidifies.

The way your air conditioner removes humidity from the air much like how beads of condensation form on your glass of ice water on a warm day. During the cooling cycle, the cold surface of your air conditioner’s evaporator coil collects moisture from the air circulating across it.

In AUTO mode, when the system cycles off and the coil begins to warm up, these moisture droplets drip into the drain pan. In ON mode, there is no time for these beads of moisture to drain because the fan is constantly running. Instead, some of the moisture evaporates and returns into your home.

Thus, AUTO mode supports proper dehumidification. But it is important to note that the thermostat setting is not the only influencing factor in how well your AC removes humidity. Other factors also weigh in, such as the size of your air conditioner in proportion to your home or building’s square footage.

ON Improves Air Filtration & Circulation

When it comes to air filtration, ON has the upper hand. ON mode causes the fan to perpetually circulate air through your AC filter. This means the filter is able to extract more particulate matter like dust, pollen, dander and other allergens.

The only downside, besides those discussed in above, is that you will need to change or clean your filters more often. But if you suffer from severe allergies, this may be a small price to pay for the added relief provided by increased air filtration.

Additionally, the increased air movement in ON mode can eradicate hot or cold spots in your rooms. You might also stay more comfortable between your air conditioner’s heating or cooling cycles. Of course, you can achieve a similar effect with ceiling fans or portable fans.

If temperature consistency is your primary concern, you might consider an air conditioner with a variable speed blower. This type of system eliminates temperature swings between cooling cycles.

In Summary

  • We recommend setting your thermostat to AUTO for the best balance of energy efficiency and comfort.
  • If you suffer from allergies, the ON setting’s increased air filtration might offer some relief.


Published on July 6, 2017 - Author: Mallory Gross

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Air Filtration DIY Tips Energy Efficiency Indoor Air Quality

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