What’s the Difference Between On and Auto Thermostat Settings?

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Temperatures have been mild enough recently in Des Moines that you may be enjoying not running your air conditioner or furnace yet. But winter is just around the corner, and when you do decide to run the furnace, what should the fan be set at? What’s the difference between the on and auto setting on your thermostat? Before delving into the pros and cons of each setting, let’s establish some quick definitions.

The on setting means your fan will continuously run 24/7, even if the unit isn’t heating or cooling the air.

The auto setting means the fan will run only when your unit is heating or cooling the air.

Now that on and auto have been defined, which setting is best for your home?

Why You Should Set Your Thermostat to On

Setting the thermostat to on keeps your home more comfortable by continuing to distribute uniform heating or cooling throughout the space. You shouldn’t experience “cold spots” in your house with the on setting, even when when your unit isn’t running through a cycle. In addition to comfort, air quality dramatically improves when the thermostat is set to on. Air is continuously pulled through the filter, clearing it of dust and allergens, which may make on the ideal function for people with asthma or allergies. Finally, you can make your unit last longer by keeping the fan on all the time. It may seem counterintuitive, but running the fan constantly actually reduces wear and tear by eliminating frequent starts and stops, similar to the way your car gets more efficient gas mileage driving on the highway versus driving in town.

The Potential Setbacks

With the fan running continuously, you may need to change the furnace filter more frequently as it will collect more dust and debris in a shorter period of time. You may also notice cold air coming from the vents during the winter. While the air temperature will be the same as the temperature in the room, it will feel cold compared to your body temperature. Lastly, running the fan all the time could potentially increase your energy bill up to $50 a month. Some HVAC professionals argue, however, that depending on the unit, you could actually save money by keeping the thermostat set to on. They say that most of the energy is used to start the motor, but very little energy is required to keep the motor running. You may want to experiment for yourself to see if on or auto saves more money on heating and cooling bills.

Why You Should Set Your Thermostat to Auto

If you have a unit that is more expensive to run the fan continuously, then cost savings are the biggest benefit for setting your thermostat to auto because it could use less energy. The furnace filter will also last longer since the air isn’t constantly being pulled through the filter for purification.

The Potential Setbacks

Your furnace filter will last longer only because it isn’t doing as much work, and the air quality of your home will diminish. The auto function doesn’t allow for even distribution of hot or cold air, meaning areas of your home probably won’t feel as comfortable. Finally, the frequent starting and stopping of the fan motor could cause it to wear out more quickly, leading to inconvenient repairs.

Ultimately, whether you should set your thermostat to on or auto largely depends on your priorities. Do you value comfort over cost or vice versa? Would you rather improve air quality or replace the filter less often? Again, depending on your unit, you may need to experiment with the thermostat settings. Choose two months of the year that have similar weather patterns and test out each setting. Try to document your comfort level throughout each month and compare your notes against your energy bills to determine if you value comfort more than cost. As always, the professionals at Lenz Heating & Cooling are happy to make recommendations based on your specific needs, so give us a call any time!