On vs. Auto: Which Thermostat Setting Is Better?

Jul 13, 2020

On vs. Auto:  Which Thermostat Setting Is Better?

Summer is here and you’re preparing to leave for a much-anticipated vacation. Everything is packed, but what about your HVAC system?  As usual, it’s hot in the Tri-Cities and you want to regulate the temperature in your home and have it cool and comfortable when you return. 

So while your house is empty, is it better to keep your thermostat in the “ON” setting or “AUTO”, also keeping in mind cost-effectiveness?

The general wisdom tends to be to keep the thermostat set to AUTO instead of ON. But is there really a difference?

Absolutely! Keeping your thermostat set to “ON” can actually cost you more money, compromise the air quality in your home, and cause more maintenance issues. 

What AUTO and ON Mean

The fan setting is what controls your AC blower. The fan that is inside your system helps to distribute air throughout your home. 

When your central air conditioning is set to the AUTO setting, your fan turns on automatically ONLY when your system is heating or cooling the air in your home. When the thermostat reaches your temperature setting, the system including the blower fan shuts off. This is the most energy-efficient option. 

When set to the ON position, the fan is CONSTANTLY blowing, even when your system is not heating or cooling the air. It is recommended to AVOID the ON setting for several reasons. They include: 

1. Higher Energy Costs

Because the fan is always running, your HVAC system is consuming more energy than when the fan just runs when your system is heating or cooling.  When you keep the thermostat set to AUTO, your system uses less energy. 

2. More Frequent Repairs 

If your AC unit is set to ON, the fan runs more often and for longer periods of time. This could increase wear and tear on your blower and lead to costly blower repairs. 

3. Increases Humidity

Your central air conditioning will not dehumidify your home as well as it should when the fan is set to ON.  When your air conditioning is set to the ON position, the relative humidity goes up, as does the dew point.  This can make for a very uncomfortable home! 

When the AC unit is constantly running, the indoor coil becomes cold. Water vapor from the air passing over it condenses in the coil. When the compressor turns off, the coil warms up. In the meantime, the water remaining on the coil will just sit there until the next cycle, with some of it evaporating and sitting in the air inside the coil housing.  So with the fan running continuously, the air passing over the coil as it warms up will evaporate that water and put it right back into the house. 

Having relative humidity at 70 percent or more in you is not a good idea. That is when mold can really get out of control. When you have the thermostat set to the fan-ON position for long stretches of time, you could potentially experience a lot of mold. 

4. Worsens Air Duct Leakage

The majority of homes leak approximately 10 percent of the air supply and 12 percent of the return air through their duct system, according to Energy Vanguard. If the fan is blowing continuously for an extended period of time, you are always losing your conditioned air, while running up your energy bills. 

5. Quickly Clogs Your Air Filter

The fan will continually pull in air through your return vents, right where your air filter is. This means it is going to grab more dust over a shorter period of time. As a result, you are likely going to have to change your air filter more frequently. 

Look to Apollo Heating and Air Conditioning for Other HVAC Setting Tips!

Would you like to know other ways you can save money with the use of your HVAC system? Maybe you want to know more general tips on how to optimize your central air settings. 

Customers like you have trusted the award-winning residential and commercial service that Apollo offers throughout the Tri-Cities. Whether it is for your home, your place of business, or an investment property, Apollo delivers a world-class HVAC system that gives you an ideally comfortable environment.

We invite you to contact Apollo Heating and Air Conditioning by calling (509) 396-COLD (2653).