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Your heating bills are climbing, and you’re wondering if that little fan switch on your thermostat could be the answer. It’s a simple toggle between “Auto” and “On,” but the difference in your monthly costs could be anywhere from $10 to over $50.

At Tuck & Howell Plumbing, Heating & Air, we’ve been helping families in Upstate South Carolina and Western North Carolina stay comfortable since 1969. One of the most common questions we hear each winter is about furnace fan settings. The answer isn’t always straightforward because it depends on your specific system, home, and needs.

Here’s what you need to know to make the right choice for your home.

What’s Actually Happening When You Switch Between Auto and On?

Your furnace has a blower motor (the fan) that pushes heated air through your home’s ductwork. The setting you choose controls when this fan runs.

Auto mode: The fan only kicks on when your furnace is actively heating your home. Once the heating cycle completes, the fan shuts off. This is the default setting on most thermostats.

Continuous (On) mode: The fan runs 24/7, moving air through your home even when the furnace isn’t producing heat.

Think of it like this: Auto is like turning on your ceiling fan only when you’re in the room. Continuous is like leaving that fan running all day and night, whether you’re there or not.

The Real Cost Difference: What You’ll Actually Pay

Let’s talk numbers, because this is where things get interesting. If you’re running an older system, switching from Auto to Continuous could seriously impact your wallet.

For older furnaces with PSC motors (permanent split capacitor): A typical older furnace fan uses 300 to 500 watts, and running it continuously can add $15 to $50+ per month to your energy bill. Over a year, that’s potentially $600 in additional costs just for constant air circulation.

For newer systems with ECM motors (electronically commutated motors): Modern variable-speed or ECM motors use about 100 watts, costing roughly $7 to $10 per month to run continuously. That’s a dramatic difference.

Here’s what matters for homeowners in our service areas: Electricity rates in South Carolina and North Carolina average around 14 to 15 cents per kilowatt-hour. These rates keep costs moderate, but the type of motor in your furnace makes the biggest difference in what you’ll actually pay.

Want to know which motor type you have? Check your furnace’s age. The U.S. Department of Energy mandated that furnace manufacturers use efficient ECM motors over PSC motors in new units starting in July 2019. If your furnace was installed before 2019, you likely have a less efficient PSC motor.

When Auto Mode Makes the Most Sense

For most homes, Auto is the winner. Here’s why:

You’ll save money on electricity. The fan only runs when needed, which means less power consumption. Running your fan in Auto mode can save about $300 per year compared to continuous operation.

Your air filters last longer. Since air isn’t constantly flowing through the filter, you won’t need to replace it as frequently. Instead of changing it every two to three weeks, monthly replacements might be sufficient.

Better humidity control in winter. When the fan runs continuously, it can make your home feel drier because it’s constantly circulating air, which can evaporate moisture from your skin and make the indoor environment less comfortable.

At Tuck & Howell, we typically recommend Auto mode for customers with older furnace systems or those primarily concerned about keeping their energy costs down. It’s the most energy-efficient option for the majority of homes we service across Anderson County, Greenville County, Spartanburg County, and our other service areas.

When Continuous Mode Might Work Better for You

Continuous mode isn’t always the wrong choice. Some situations actually benefit from 24/7 fan operation.

If you have a newer furnace with an ECM motor: The energy penalty drops significantly. You might only spend an extra $8 to $18 monthly, which could be worth it for the benefits.

If you have rooms that are always too hot or too cold: Multi-level homes (common in the Upstate and Western North Carolina) often have temperature inconsistencies. Keeping the fan running helps even out these hot and cold spots by constantly mixing the air.

If someone in your home has allergies or respiratory issues: Continuous air circulation means your air is constantly passing through the filter, capturing more dust, pollen, and other particles. This can genuinely improve indoor air quality.

If your home has poor insulation: Constant air movement can help compensate for drafts and temperature variations by keeping air circulating to all areas of your home.

However, there’s an important consideration many homeowners miss: if you set your fan to continuous mode in winter and notice cool drafts, that’s a red flag. The fan is circulating unheated air, and this can make cold-sensitive individuals uncomfortable since air particles moving around lose heat in the process.

What About Your Ductwork? This Changes Everything

Here’s something that often gets overlooked: even well-sealed HVAC systems experience minor leakage, primarily in the ductwork where tiny holes and gaps allow air to escape. When your fan runs continuously, it’s constantly pushing air through these small leaks, which increases energy loss.

If you’re considering continuous fan operation, it’s worth seeking ductwork services to ensure your system isn’t wasting energy through preventable leaks. We’ve seen situations where homeowners paid for constant air circulation but lost much of that air through poorly sealed ducts.

The Filter Factor: Hidden Costs You Need to Know

Whichever setting you choose affects how often you’ll buy and change filters. It’s a smaller expense than your electricity bill, but it adds up.

With Auto mode: Plan on monthly filter changes in most homes.

With Continuous mode: You might need to replace filters every two to three weeks, especially if you live in an area with high pollen counts or have pets. That’s potentially 18 to 24 filters per year instead of 12.

Dirty filters don’t just cost money. They make your blower motor work harder, which uses more electricity and puts extra strain on the system. If you notice your energy bills climbing or your furnace making unusual noises, a clogged filter is often the culprit.

How to Decide What’s Right for Your Home

Start by answering these questions:

How old is your furnace? If it was installed in 2019 or later, you likely have an ECM motor, making continuous operation more affordable. Older systems will cost significantly more to run continuously.

Do you notice uneven heating? If your bedroom is always freezing while the living room is toasty, continuous fan operation might solve this problem.

What’s your budget? If you’re watching every dollar on your utility bills, Auto mode will almost always be the more economical choice.

Does anyone in your home have allergies or asthma? Better air filtration from continuous operation might be worth the extra cost for improved health and comfort.

Have you noticed cool drafts when the fan runs? This suggests air leakage in your ductwork and means continuous operation is wasting energy you’re paying for.

We at Tuck & Howell recommend starting with Auto mode and switching to Continuous for a billing cycle to compare the actual cost difference on your specific system. Your real-world results will tell you if the comfort benefits justify the added expense.

What About the Latest HVAC Changes? Do They Affect Your Fan Settings?

You might have heard about refrigerant changes happening in 2025. Here’s the good news: the ongoing refrigerant transition from R-410A to newer A2L refrigerants like R-454B affects air conditioning units but does not change furnace blower fan operation or recommendations. Your existing furnace and your choice between Auto and Continuous remain unaffected by these industry updates.

Signs Your Furnace Fan Needs Professional Attention

Sometimes the Auto vs. Continuous question becomes irrelevant because something’s wrong with your system. Watch for these warning signs:

• Unusually high energy bills when you haven’t changed your thermostat settings
• Strange noises when the fan runs, like grinding, squealing, or rattling
• Inconsistent heating that doesn’t improve even with continuous fan operation
• The fan doesn’t turn off even when set to Auto
• Weak airflow from your vents compared to what you normally experience

These issues often point to problems like motor wear, duct leaks, dirty coils, or failing components that need expert diagnosis. At Tuck & Howell, our technicians can identify whether your system needs repair, maintenance, or if it’s time to consider replacement options.

Making the Switch: How to Change Your Furnace Fan Setting

Changing your fan setting is simple. Look at your thermostat and find the “Fan” section. You’ll see two options:

• Auto (sometimes shown as a clock icon)
• On (sometimes shown as a fan icon)

Select your preferred option. The change takes effect immediately. Try running your system on Continuous for one complete billing cycle, then compare that bill to a month when you used Auto. This gives you real data about what the setting costs in your specific home.

Your Furnace Deserves Regular Care Regardless of Fan Settings

Whether you choose Auto or Continuous, your furnace needs annual maintenance to run efficiently. We’ve been serving families in Greer, SC, and the surrounding communities since 1969, treating every home with the same care we’d give our own.

Our preventative maintenance includes checking your blower motor, inspecting ductwork for leaks, testing airflow, examining electrical connections, and replacing filters. These services help ensure your system runs efficiently no matter which fan setting you prefer.

Frequently Asked Questions

Will running my furnace fan continuously wear it out faster? Not necessarily. Modern ECM motors are designed for extended operation and may actually experience less wear because they avoid frequent start-stop cycles. However, older PSC motors weren’t built for continuous use and may wear out faster.

Can I run my furnace fan on Continuous in winter but Auto in summer? Absolutely. Many homeowners find continuous operation more beneficial during the cooling season for humidity control and switch to Auto for winter heating. Adjust your settings seasonally based on your comfort needs.

How do I know if I have an ECM motor or a PSC motor? Check when your furnace was installed. Systems installed after July 2019 typically have ECM motors. For older systems, look at the motor label inside your furnace’s access panel, or contact us at Tuck & Howell for a professional assessment.

Will continuous fan operation help with my allergies? It can help. Continuous air circulation means more frequent filtering, which can reduce airborne allergens. However, this only works if you’re changing your filter regularly. A dirty filter with continuous fan operation can actually make air quality worse.

Does the outside temperature affect which setting I should use? Cold temperatures don’t directly affect the setting choice, but if you’re experiencing very cold weather and notice cool air coming from your vents on Continuous mode, switch to Auto. The fan is circulating unheated air, which wastes energy and reduces comfort.

What if my energy bill spikes after switching to Continuous? This is normal if you have an older PSC motor. Calculate the actual cost increase and decide if the comfort benefits justify the expense. If the spike seems excessive (more than $50 for a PSC system or more than $20 for an ECM system), contact a professional to check for underlying issues like duct leaks or motor problems.

Find Your Perfect Balance Between Comfort and Cost

There’s no universal answer to the Auto vs. Continuous debate. Your best choice depends on your furnace type, home layout, health considerations, and budget priorities.

What we can tell you from our 50+ years of experience at Tuck & Howell Plumbing, Heating & Air: most homeowners benefit from Auto mode for cost savings, while those with newer ECM motors and specific comfort or air quality needs might find the modest extra cost of Continuous mode worthwhile.

The most important thing? Regular maintenance of your heating system. A well-maintained furnace runs more efficiently regardless of fan settings, saving you money and preventing unexpected breakdowns during the coldest days.

Ready to optimize your home’s heating system? Contact Tuck & Howell Plumbing, Heating & Air today. Our expert technicians serve homeowners throughout Anderson County, Buncombe County, Spartanburg County, Pickens County, Greenville County, Laurens County, Polk County, Henderson County, Greenwood County, Wayne County, and Oconee County. We’ll help you understand your specific system and find the right balance between comfort and efficiency for your home. Call us today to see “Howell” we’re different.