HVAC Fan: Should You Keep It Running on Auto or On?

Have you ever felt like you have stepped out on the sands of Sahara from a cool breezy beach while moving from one corner of your house to the other? If the answer is yes, you need to get your HVAC fan running to eliminate this temperature discrepancy.

Your heating, ventilation, and air conditioning systems come equipped with a fan that you can control with your thermostat. HVAC blower fans are used to circulate air in a room and remove hot and cold spots until the temperature set on your thermostat is achieved.

These fans have two working modes, Auto and On, and there is always this huge debate about which one works best. However, both these modes have their advantages and disadvantages, and there is no exact answer to whether you should keep your AC fan On or Auto. Moreover, the latest smart thermostats also allow for custom fan settings!

Read on to learn which HVAC fan setting fits your needs best.

HVAC Fan Modes — Auto & On

HVAC fans provide ventilation, help maintain indoor air quality and increase thermal comfort. Let’s dig into the details of Auto and On mode, how each of them works, and which one you should choose.

What Is Meant by the ‘On’ Mode?

The “On” mode means your HVAC fan will keep running 24/7. This setting implies that your HVAC system’s blower will constantly work even when the AC is not heating or cooling.

There are a few upsides and downsides to running an HVAC fan continuously.

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Pros of Using the ‘On’ Feature

1. Better Air Circulation

While your air conditioner heats or cools the air, it cannot circulate this air properly on its own. A fan distributes the conditioned air better around your house and helps to remove any hot and cold spots.

Another problem regarding air circulation is that hot air rises upwards, whereas cold air lies close to the ground. This can cause hot air to accumulate in the upper stories of your home, thus increasing the temperature here. So, keeping your AC fan on continuously will effectively help circulate air on upper floors all the time, not just when your cooling is on.

Keeping an AC fan on means it won’t have to start and repeatedly stop, which will reduce stress from the fan. Believe it or not, this practice can help extend the life of your HVAC blower.

3. Fresh Odorless Air

Temperature levels stay moderate during spring and fall, especially in sealed buildings and spaces with mostly closed windows. In such a situation, the air conditioning may be switched off, resulting in the air being stuffy. Leaving your HVAC fan on can help you keep the air fresh and eliminate any odors.

Keeping an AC fan on all the time means air passes through your AC filters more frequently. This can help remove indoor airborne contaminants like pollen, dust, bacteria, and mold.

However, the benefit you gain from air filtration depends on the type of air filters installed in your HVAC system and how well you keep them maintained. Filters with a high MERV rating can effectively remove most of the tiny particles from the air.

Cons of Using the ‘On’ Feature

Listed below are some downsides of using the “On” mode of your HVAC fan.

1. High Energy Bills

Keeping your air handler fan on all the time will surely rack up your energy bills. Depending upon the size, model, and duration an AC has been in use, an air conditioner can utilize around 500 Watts or more when running an HVAC fan only. This can accumulate to 360 kWh per month.

2. Frequent Need to Change the Air Filter

When air from a room continuously gets circulated through HVAC air filters, the filters get clogged faster. You would need to clean the air filter more often or change them frequently.

3. Hot Air in Summer

Ducts installed near an attic or close to walls can fill up with hot air during summer. This air gets circulated in your house when the fan is constantly running. As a result, your room ends up getting hot, and the AC turns on more frequently to bring down the room temperature.

4. Cold Air in Winter

When you turn on the fan of your air conditioner during winter while the heating is off, you will feel a cold breeze coming out of your vents. Although air temperature remains the same, you still experience a cold sensation.

5. Inefficient Humidity Removal

Moisture is removed from the air during cooling. Air passes over evaporator coils, and moisture condenses on the coils in the form of droplets. When the system stops cooling, the coils warm up and water droplets drip down. This water should be expelled out of your home.

However, running the HVAC fan continuously causes part of this water to evaporate back into the air, thus causing a hindrance to the effective removal of humidity.

What Is Meant by the ‘Auto’ Mode?

Setting your HVAC system fan to “Auto” means running it only when the system is heating or cooling. For example, after your thermostat reaches the required temperature, the system turns off, including your AC’s fan.

Pros of Using an HVAC Fan’s ‘Auto’ Feature

1. More Energy Efficiency

Running your AC fan on the Auto setting means it will only run when the system is cooling or heating. So, the fan runs for the minimum period possible. It is thus more energy efficient to set your fan on Auto than continuously running the fan. As a result, you get lower energy bills.

2. Better Dehumidification

Since the HVAC fan shuts off in Auto mode as soon as cooling stops, moisture droplets on condensation coils can easily drip down into the drain pan located beneath these coils. From there, moisture is effectively discarded outside the house. This helps you achieve perfect humidity levels in your home.

Cons of Using the ‘Auto’ Feature

Although this mode provides better humidity control and saves money, a few things might cause a problem for you.

1. Uneven Temperature

Lack of circulation after the system shuts down means hot air will continue to rise, and cold air will stay in the lower part of the room, causing uneven temperature.

2. Quicker Wear Out

Setting your HVAC blower to Auto mode will cause the fan motor to turn on and off frequently. This will cause the fan motor to wear out soon and cut its life short.

Verdict on AC Fan Mode: ‘On’ or ‘Auto’?

There is no definite answer to questions like “how long should my HVAC fan run per hour?” or “Should my fan be on “Auto” or “On”?”.

Running the fan frequently or setting the AC fan to “On” or “Auto” is a personal choice as both these modes have some advantages and disadvantages.

However, the only factor that matters here is the humidity levels of the area you live in. If you live in an area where humidity levels are high, setting your HVAC fan to “On” can lead to inefficient humidity removal and cause mold growth. In such regions running the AC fan on “Auto” is safe.

However, some options can help you eliminate the disadvantages while you make the most of the advantages!

• Smart Thermostat: Using smart thermostats, you can also set custom timers to run your fan only at required settings. You can choose how long your AC fan will run every hour irrespective of the heating or cooling cycles.
• Variable Speed Technology: Incorporating variable-speed fan motor technology into your HVAC is another great option. A variable-speed fan motor operates at different speeds to regularize your home’s airflow in the best possible way.

With variable speed technology, the AC fan runs continuously to circulate the air, but because your system has the ability to run at lower capacities, it is energy efficient. It means your energy bills won’t be skyrocketing because of your AC fan, and the system won’t have to turn on and off repeatedly. This system thus provides better humidity control, long fan motor life, even temperature, and continuous filtration.

Frequently Asked HVAC Fan Questions

All air conditioner components are subject to wear and tear over time, and several issues can occur when switch on your AC fan. There might be questions you have in mind about how long or when the fan should be running. Here are the answers to the most asked questions.

Why Your HVAC Fan is Not Working?

If your air conditioner is on, but your fan is not working, the reason behind it could be:

A capacitor is a cylinder-shaped small component of an air conditioner that stores electrical energy and provides it to the system when required. There are several capacitors in an air conditioner. If the capacitor responsible for sending energy to the fan motor is dead, the HVAC fan does not turn on. Therefore, you would need to get it replaced.

Sometimes, because of overheating, the circuit breaker can get tripped. This results in your HVAC fan not working. Simply flipping the switch at the circuit breaker will fix this issue.

Fan motors can get overworked, and when paired with a lack of maintenance, the motors wear out and stop working. These are expensive to repair and should be replaced by a professional.

If not cleaned and replaced periodically, the air filters can get blocked. The blockage puts more stress on the fan, causing it to shut down. Keeping the filters clean can solve this problem.

This part of an HVAC unit controls the electricity flow throughout the air conditioning unit. Sometimes these contractors wear out with time and eventually burn out. This can result in your HVAC fan not working. Proper maintenance is required to keep contractors in good working condition, but getting it repaired by an HVAC professional is your only option if it is worn out.

Do HVAC Fan’s Bring in Outside Air?

No, the AC blower fan does not bring in fresh outside air generally. It circulates the air already present in a room to improve the airflow and remove hot and cold spots.

Does the Fan Always Run When the Heat Is On?

If you have set your fan on Auto mode, it will turn on when the system turns on for heating or cooling. On the other hand, if the fan is set to On mode, the HVAC fan won’t turn off even when your AC is not cooling or heating.

Is It OK to Run the HVAC Fan Continuously?

Yes, It is completely safe and possible to leave your HVAC fan on continuously. It will help circulate the air and keep the air clean as the air frequently passes through the air filters of the AC unit.

How Much Does It Cost to Run an HVAC Fan?

An average fan motor is 500 watts, and if it is run 24/7 for a month, it uses 360,000 watts hours or 360-kilowatt hours (kWh). One kWh costs around $0.12 in the US. So, it will add up to $43.2 per month and about $518 per year.

HVAC Fan Speed Too High: What Should You Do?

If your HVAC fan speed seems too high, it can cause issues with the system. In this case, here’s what you need to do:

• Turn off the power of the system.
• Next, use your unit’s manual to locate the pulley, blower motor, and set screw of the system.
• First, you need to loosen the screw, move the pully in the anti-clockwise direction, and set the screws back.

Take Away

HVAC fans are essential for adequate ventilation and air circulation in your home. You can choose to set your HVAC blower fan to On mode if you want to get rid of hot spots and stale air effectively. On the other hand, if saving money and efficient humidity removal from your space is essential, Auto mode is more suitable for you. Irrespective of the fan mode you choose, do not forget to do proper maintenance of your HVAC system for it to work properly.

Originally published at https://cielowigle.com on June 15, 2022.