Name: Prairie Heating and Air
Address: Post Falls, ID, USA, Post Falls, Idaho, 83854, US
Telephone: 208-619-6480
Price range: $$

“ON” vs. “AUTO” Explained for North Idaho Homeowners

If you’ve ever stood in front of your thermostat and wondered, “Should my fan switch be set to ON or AUTO?” you are not alone. It’s one of the most common questions we get from our neighbors here in Coeur d’Alene, Post Falls, and Spokane.

At Prairie Heating and Air, we believe you shouldn’t need a degree in thermodynamics to keep your home comfortable and you definitely shouldn’t be paying more on your Avista or Kootenai Electric bill than you need to.

While national home blogs might give you cookie-cutter advice, the right answer actually depends a lot on our unique Inland Northwest climate. Let’s settle the “ON vs. AUTO” debate once and for all, look at how much energy that little switch actually uses, and figure out the best choice for your home.

What Do “ON” and “AUTO” Actually Mean?

First, let’s clear up exactly what that switch controls. This setting only controls your indoor blower fan. The fan responsible for pushing air through your ductwork and vents. It does not turn your actual furnace or air conditioning unit on and off.

AUTO: The fan only runs when your system is actively heating or cooling the air. Once the house reaches your target temperature, the whole system (fan included) shuts off.
ON: The blower fan runs continuously, 24 hours a day, 7 days a week, regardless of whether your system is actively heating or cooling the air.

How Much Energy Does the “ON” Setting Use?

Let’s talk dollars and cents. A standard HVAC blower fan uses anywhere from 400 to 800 watts of electricity per hour depending on the age and size of your system.

If you leave your fan set to ON 24/7/365, it will run for 8,760 hours a year.

Even at the Inland Northwest’s relatively affordable electricity rates, running a standard fan motor non-stop can add $30 to $50 a month to your energy bill.

Over a year, you’re looking at an extra $360 to $600 just to keep the air moving!

The Pros and Cons of Setting Your Fan to “ON”

While paying extra on your electric bill doesn’t sound appealing, there are a few very specific reasons you might want to run your fan continuously.

The Pros:

Better Air Filtration which is a big deal in North Idaho: Your HVAC system only filters the air when the fan is running. During late summer when wildfire smoke rolls into North Idaho and Eastern Washington, switching your fan to ON (coupled with a high-quality filter) acts as a whole-home air purifier, constantly scrubbing smoke and allergens from your air.
Even Temperatures: If you have a multi-story home in Hayden or Rathdrum that struggles with a hot upstairs and a freezing basement, running the fan constantly mixes the air and helps eliminate hot and cold spots.

The Cons:

Higher Energy Bills: As mentioned, it costs hundreds of dollars a year.
Winter Drafts: When it’s 15 degrees outside in January, your furnace isn’t constantly burning gas. If the fan is set to ON, it will blow unheated, room-temperature air through your vents between heating cycles. To your skin, this can feel like a chilly draft.
Faster Wear and Tear: Blower motors are tough, but running them 24/7 puts extra miles on the system, potentially leading to premature repairs.

The Pros and Cons of Setting Your Fan to “AUTO”

For the vast majority of homeowners, AUTO is the recommended setting. Here is why:

The Pros:

Maximum Energy Savings: You aren’t paying for electricity you don’t need. The fan only runs when it’s supposed to.
Better Dehumidification: During our hot summer stretches, your AC pulls humidity out of the air. When the AC cycles off, the moisture stays on the indoor coils and eventually drains away. If your fan is set to ON, it blows that moisture right back into your house before it can drain, making your home feel muggy.
Longer Lifespan: Giving your blower motor a chance to rest means it will likely last longer.

The Cons:

Less Filtration: The air is only being filtered during active heating or cooling cycles.
Stagnant Air: Once the desired temperature is reached, the air stops moving, which can sometimes lead to stuffy rooms.

Is There a Compromise?

Yes, if you have a newer, smart thermostat (like an Ecobee or Nest), you might notice a third option: CIRCULATE.

This is the ultimate sweet spot. The circulate setting tells your fan to run for a specific amount of time every hour (usually 15-20 minutes) even if the heating or cooling doesn’t kick on. This gives you the best of both worlds: it keeps the air filtered and mixed, but saves you from the massive energy bill of running it 24/7.

Prairie Heating & Air Expert Tip: If your system has a variable-speed blower motor (an ECM motor), leaving it “ON” uses significantly less energy than an older system, costing only a few dollars a month. If you aren’t sure what kind of motor you have, ask us during your next tune-up!

Which Should You Choose?

As a general rule of thumb for our North Idaho and Eastern Washington neighbors, keep your thermostat set to AUTO to save money and extend the life of your equipment.

The only time you should switch it to ON is:

During heavy wildfire smoke days to keep your indoor air clean.
If you are doing a dusty home renovation or intense spring cleaning.
If you have a lot of guests over and the air feels stagnant.

Need a Little Extra Help With Your Comfort?

At Prairie Heating and Air, we were raised in crawlspaces, not boardrooms. We know what works for homes in our specific climate, and we’re dedicated to giving you honest, transparent advice.

If your home is struggling with hot and cold spots, your indoor air quality feels poor, or you think your blower motor might be drawing too much power, we’ve got your back.