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On vs. Auto: One of These Thermostat Settings Costs You Big Time

Have you ever looked at your thermostat and thought, “What the heck is the difference between the ‘On’ and ‘Auto’ fan setting anyway? And which one should I keep the thermostat set to?”

If you haven't, you should.

Because one of these fan settings can increase your electrical bill every month and lower the lifespan of your heating/cooling system.

Let us explain.

On vs. Auto: Here’s the difference

The two settings tell your central cooling/heating system how to use the blower. The blower is the part in your system’s inside unit (usually in your attic) that circulates cooled/heated air in your home.

AC Diagram

Diagram of a blower pulling in warm return air, cooling the air and blowing the cold air out the supply vents.

When set to “On” the blower works continuously—24/7. Meaning that it’s always circulating air regardless of whether the air is being cooled or heated.

When set to “Auto” the blower runs only (or “automatically”) when you need to cool or heat air. As soon as your thermostat reaches the desired temperature, the blower turns off alongside the rest of your heating/cooling system.

So now this question comes: Which fan setting should you leave your thermostat on?

While “On” has its uses, it’s best to leave your thermostat to “Auto”. Here’s why.

Why the “On” setting can cost you

It’s a no-brainer: If “On” causes the blower to run continuously, it can increase your electrical bill by about $8 a month (almost $100 a year), depending on the size of your system.

But the continuous use also wears down the blower, shortening its lifespan and increasing the chances it will break down and need repairing.

Of course, we can help you if that ever happens. But we’re sure you would want that to happen later rather than sooner.

When in doubt, leave your thermostat to “Auto”!

George Brazil has been keeping Phoenix-area homes comfortable and energy-efficient since 1955. Contact us online for more information about any of our services.