Some homeowners naturally worry about the risks of a breakdown if they run the fan all the time, but this will not be a concern for you if your HVAC system was properly installed and maintained. The only possible exception here is a very old fan system, which should generally be replaced in the near future anyways.
They should not be left on all the time. Some of the more advanced thermostats might use the fan to better circulate the air post-AC or heat running or pre-cool the home a little by running the fan. But in normal operation, it only runs with the furnace or AC does.
Since the AUTO setting means the fan is only engaged when the system is on, rather than constantly blowing, AUTO is the most energy-efficient option between the two settings.
If we assume an average of 10 hours on and 14 hours off per day, energy costs are reduced by 60% to about $18 per month or $215 per year. Bottom line – If you run the fan in AUTO mode, you'll save about $300 per year.
This approach can reduce wear and tear on the air conditioning equipment because the fan doesn't have to start and stop as often. Running the fan on the AC all the time also helps maintain a more consistent and even temperature throughout your home because air is constantly circulating, eliminating hot and cold spots.
Cons to Keeping Fan Continuously Running:
It could cost you hundreds of dollars a year. The average unit has a 500 watt fan, which uses almost as much energy over the course of the year as a refrigerator, resulting in a $50/month bill.
Generally, running the fan for 15-20 minutes per hour is sufficient for adequate air circulation. However, longer fan run times may be necessary for specific conditions like hot and humid weather or improved air filtration.
Which Thermostat Setting Is Best: On, Auto, or Circulate? Given the amount of money it costs in increased utility bills and filter purchases to keep your AC fan running constantly, most of the time, you'll want to keep the fan in the “auto” position.
Constantly running your fan will move a lot more air through your filter. It'll need to be changed more often. The upside is that the air your family breathes will be cleaner and healthier, and so will your home.
Fans that are left on constantly can use more electricity than they should, and their blades will become dull quickly, even without being used. – Clean it regularly. The one major risk that you have when running an electric fan all day long is dust and debris building upon its surface.
Therefore, always running your HVAC fan helps you feel cooler in the summer, even if you don't have air conditioning. But you can also turn the thermostat up a few degrees and still achieve a sufficient comfort level.
A fan's housing will get warm after prolonged use due to the fan's motor generating heat when converting electricity into movement. This heat is why many people think it is unsafe to leave fans running; however, it is normal and will dissipate from the fan's housing and not exceed a safe limit.
Unfortunately, operating the fan continuously during the summer can lead to comfort, health, and property damage risks – mainly because of high indoor humidity.
On a normal summer day, you can expect your air conditioner to run somewhere around 15 minutes during every cooling cycle. But if your cooling cycles are lasting 30 minutes, an hour, or all day long, there's a good chance that something is amiss with your system.
Running the HVAC fan by itself usually does not bring in outside air. The fan's job is to move air around your home. When you set your HVAC to “fan” mode, it circulates the air that's already inside your house. However, some systems have a fresh air intake that can bring in outside air when the fan is running.
Pros of Continuous Fan
In addition, this practice holds significant benefits for homes containing people with allergies, asthma or any other respiratory conditions. This is because more air circulation means a greater number of passes through your filtration system, leading to higher air quality in the process.
"AUTO" is the more energy-efficient option, as it runs the fan only when heating or cooling is actively needed. "ON" keeps the fan running continuously, which can help with air circulation and filtration but may consume more energy.
Pros for “Auto”: If you set your furnace fan to “auto,” the fan will only run when the system tells it to in order to keep your home as warm as you want it based on your thermostat settings. This means it's consuming less energy than when it runs non-stop, which means lower furnace bills.
A common misconception about furnaces is that running your HVAC fan nonstop will cause it to give out early. However, this isn't the case, especially with newer units designed to run 24/7. Consistent fan operation should not be an issue if your HVAC system was installed by experienced professionals.
Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously. There is better dehumidification in your home during the summer months. When your fan is set to AUTO, moisture from cold cooling coils can drip and be drained outside.
For example, a standard central air conditioner, like the one you probably have in your house, consumes between 3,000 and 3,500 watts of electricity per hour. That same AC when only the fan is running consumes 500 watts of electricity per hour. That's an enormous difference!
You can run the fan independently of the AC by switching the fan to “Fan On,” which will keep the blower fan running whether there's a demand for cooling or not. The AC can still come on, but you'll have continuous air circulation when it's not. You can also shut the AC off completely so only the fan runs.
A constantly running fan will increase your utility bills and produce more humidity in your home because it will just blow warm air around without the AC absorbing moisture and heat.
Most homeowners don't realize that your air conditioner actually has two responsibilities: to cool and dehumidify your home. But if you're leaving your thermostat fan setting to “ON”, you prevent your AC from removing as much moisture from your home.