Your HVAC system includes a blower fan that can be controlled with your thermostat. These fans are used to send the conditioned air in the home, circulate air throughout the home, and achieve even temperatures. The fan has two working modes: Auto and On. Both modes have their pros and cons, which can help lead you to a decision on which to use.
Auto Mode
What is Auto mode?
Setting your HVAC fan to Auto means that it will only run when the system is heating or cooling. Once the desired temperature is reached, the fan will shut off along with the rest of the system.
Advantages of Auto mode
One advantage using Auto mode is better dehumidification. The job of the condenser fan is to pull outdoor air through the condenser coil, allowing the air to absorb heat energy from the home and release it outside. By having the fan shut off when the cooling stops, moisture droplets on the condensation coils can easily drip down into the drain pan. From there, moisture is effectively discarded outside of the house, helping your home reach ideal humidity levels.
Another benefit is higher energy efficiency. Running the fan on Auto means it'll only run when the system is cooling or heating, so the fan runs for the minimum amount of time possible. As a result, you get lower energy bills. Running the fan on Auto could actually save you around $300 per year.
Disadvantages of Auto mode
One con of using Auto mode is uneven temperature across your home. Lack of circulation after the system shuts off means that hot air will continue to rise and cold air will stay in the lower parts of the house, causing a temperature imbalance.
By having the fan turn on and off more frequently, you also run the risk of more wear-and-tear. Constant stops and starts will cause the fan motor to wear out sooner and cut its life short.
On Mode
What is On mode?
Setting your HVAC system to On mode means that it will constantly run, even when the system is not heating or cooling.
Advantages of On mode
A big advantage of using On mode is better air circulation. While your HVAC system heats or cools, the fan works to distribute the tempered air around your house and remove any hot or cold spots. Keeping the fan on even when the rest of the system is off will continue this air circulation, even though the air is not conditioned. Additionally, keeping the fan on will help circulate air on upper floors where hot air might get stuck while the AC isn't on.
While air is continuously circulating and passing over your AC filters, you will also have improved air quality. A healthy indoor air quality level helps remove indoor airborne contaminants such as dust, bacteria, mold, and pollen. This will also ensure that the air is fresh and odorless.
A third benefit of keeping the fan on is increased life span of the unit. Without having to repeatedly start and stop, there will be less stress on the fan which can help extend the life of the blower.
Disadvantages of On mode
While keeping the fan on will reduce wear-and-tear, it will also give you higher energy bills. Like any machine or electricity-powered item in your home, running it often will cost more money.
Next, because air is always passing through the filter, you will need to clean or change the air filter more often.
Another disadvantage of On mode is inefficient humidity removal, as moisture is typically removed during cooling. As air passes over the evaporator coils, moisture condenses on the coils in the form of droplets. When the system stops cooling, the coils warm up and the water drips down and is expelled out of the home. By always running the fan, the water will continuously evaporate back into the air, thus affecting the removal of humidity.
Finally, you may feel more hot air in the summer and cold air in the winter. 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. (This would also cause higher energy bills). On the other hand, you will feel a cold breeze coming out of the vents when the fan is on without the heat during winter.
Takeaways
One factor to consider when deciding between Auto or On mode is the humidity level of the area you live in. For example, if you live in an area with high humidity levels -- like Philadelphia -- setting the fan to Auto might be a better option. On mode can lead to inefficient humidity removal and cause mold growth.
Overall, setting your HVAC system to On or Auto is a personal choice dependent on the factors listed above. If you are more concerned with higher efficiency and lower bills, you should probably opt for Auto mode. If better air circulation and indoor air quality is important to you, then On mode is a good option.
If you live in the Delaware Valley/Greater Philadelphia area and would like to find comfort within your home, visit our website or give us a call at 215 - 245 - 3200 to learn more.
