The Pros and Cons of Running Your AC Fan Continuously vs. Auto Mode

If you’ve ever played around with your HVAC thermostat settings, you may have noticed a small toggle called “Fan Mode” with two options: “Auto” and “On” (or “Continuous”). While it may seem minor, this setting can actually have a big impact on energy efficiency, indoor comfort, and even air quality. Not sure which one is better for your home in Southern California? Let’s break it down.

What Does “Fan Auto” Do?

In auto mode, your HVAC system’s fan only runs when the air conditioner or heater is actively cooling or heating your home. Once the desired temperature is reached, both the compressor and fan turn off.

This is the default setting for most homes and is designed for energy efficiency.

What About “Fan On” or “Continuous” Mode?

In continuous mode, the system’s blower fan runs 24/7 regardless of whether heating or cooling is active. This setting circulates air at all times, even when the system isn’t conditioning the air.

While that may sound like overkill, there are several reasons why some homeowners prefer this setting, especially during allergy season or in homes with uneven temperatures.

Pros of Running the Fan Continuously

• Better Air Circulation: Running the fan non-stop can help eliminate hot and cold spots in the home and keep air moving through rooms that are further from the vents.
• Improved Air Quality: If your system has a high-quality air filter or purifier, keeping the fan running can help trap more dust, allergens, and pollutants.
• Even Humidity Levels: Especially in larger homes, continuous airflow can help maintain consistent humidity throughout the space.
• Less Wear on the Compressor: Some argue that frequent short cycling (as in auto mode) wears out the compressor more than running the fan consistently.

Cons of Continuous Fan Mode

• Higher Energy Bills: Since the fan is always running, it uses more electricity even when no heating or cooling is needed. This can add up quickly in Southern California homes.
• Increased Filter Maintenance: Your filters will clog faster, especially during fire season or dusty weather. That means more frequent replacements.
• Unwanted Air Movement: During colder months, continuous airflow might create drafts that feel uncomfortable.

When Is Auto Mode a Better Choice?

In most cases, auto mode is more energy-efficient and puts less strain on your HVAC system. It’s a smart choice if:

• You’re looking to reduce your electric bill
• Your indoor air quality is already good
• Your home has fairly even temperatures in all rooms

If you're already doing regular maintenance, auto mode is usually sufficient for most Southern California households. Here’s why HVAC maintenance is crucial if you haven’t checked your system lately.

When to Use Fan “On” Mode

Fan “On” mode may be a good idea if:

• You or a family member has allergies or asthma
• You have a whole-home air purifier or HEPA filter
• Certain rooms feel too warm or cold compared to others

Just make sure to clean or replace your air filter more frequently. Learn more about the importance of clean HVAC filters.

There’s no one-size-fits-all answer. For most homes, auto mode is the ideal balance of comfort and efficiency. But during certain seasons — or with the right indoor air quality setup fan “on” mode might offer benefits worth the extra cost.

Still not sure which mode is right for your HVAC setup? Contact Smartchoice Service at (714) 465 1135 or schedule a quick HVAC evaluation with our team of experts.