Your thermostat has two settings that control the HVAC fan that circulates heated and/or air conditioned air throughout your space. You can set it to AUTO, which automatically turns the fan on when your AC or furnace is running. Or, you can set it to ON, which tells the system to keep the fan running all the time.
Which should you choose? Let’s take a look at the pros and cons of running the HVAC fan 24 hours a day, versus only when your heating or cooling system is operating.
Benefits of keeping the HVAC fan ON
More consistent temperatures with the HVAC fan on
When the HVAC fan runs constantly, it has a chance to keep moving heated and cooled air evenly throughout every area of your home or commercial space. That can help to eliminate hot or cold spots and improve comfort.
Running the HVAC fan can eliminate stuffy air & control odors
During spring and fall when temperatures are moderate, your heat or air conditioning may not be running very often, if at all. Especially in city buildings that are well sealed and may not have windows that open, the indoor air can get stuffy with a lack of air circulation. Running the HVAC fan can help keep the air feeling fresh, and also help to dissipate odors.
Improved air quality with constant filtration
When the HVAC fan runs all the time, more air is circulated through your HVAC filters (and air purification systems if you have them), which can help to reduce airborne contaminants. That can mean less allergens like pollen and dust, VOCs, pollution, and even mold and bacteria that cause illness.
One caveat to be aware of: the benefit you gain from filters depends a great deal on the type of filter your HVAC system has. Standard HVAC filters aren’t meant to trap particles as tiny as viruses, for example, or even some types of pollen. They are primarily meant to keep dust and debris out of your HVAC system. However, filters with a higher MERV rating can remove more types of particles, as long as your system can accommodate them.
If you have an air purification system installed in your HVAC ducts, you will benefit much more from keeping your HVAC fan running.
Learn more:
Facts About Air Filters and Allergies
IAQ Alert: Is Your HVAC System Contaminated?
Less stress on the HVAC fan motor
It may surprise you to learn that running the HVAC fan all the time can actually extend the life of the fan. That can be true because it eliminates the stress of the motor frequently turning on and off every time your furnace or AC starts up or shuts down.
Downsides of using your HVAC fan all the time
Higher electricity costs
Running the HVAC fan 24/7 may use quite a bit more electricity than running it only when your HVAC system is operating. Depending on your space and your system, that could cause a noticeable jump in your electric bill.
More frequent filter changes needed
With air circulating through your space, your ducts and your HVAC filters, those filters are going to get clogged faster. You’ll need to check and change or clean your filters more frequently.
Here’s some help with how to do that:
Fall Furnace Maintenance: How to Change Your Furnace’s Air Filter
Why and How to Change an AC Filter
Air temp from the registers when the HVAC system’s not running
When your furnace/air conditioner fan is running but the heating/cooling system is not, the temperature of the air coming from your registers may be warmer than you’d like in summer or cooler than you’d like in winter. That might not be a big problem unless you’re sitting right next to the register, but it’s something to keep in mind.
Less humidity control in summer
Not to get into the technical details, but suffice to say that the air conditioning fan blowing all the time can actually impede your air conditioner’s ability to control humidity in summer. If you notice that happening, you can decide to turn the fan back to AUTO until the problem is resolved.
So which HVAC fan control option should you choose? It depends on your situation and your priorities.
Also, be aware that no matter which way you set your fan, there’s something else you can do to optimize your comfort and keep your system performing efficiently and effectively: get regular maintenance.
HVAC maintenance helps keep your systems performing well
Have your heating and cooling systems inspected, cleaned, and tuned up at least every year, and possibly more often depending on your system and its usage. The most cost-effective way to do that is with a yearly maintenance agreement that’s customized to your specific needs. It’s a small investment that pays off in big ways:
- Your system stays in good condition, so you can prolong the life of your equipment.
- Your equipment runs more efficiently, which reduces energy consumption.
- Minor issues get fixed proactively, so they don’t turn into bigger, more expensive problems.
- Maintenance helps to prevent system downtime that disrupts your home or business.
If you’re in the NYC metro area, get a quote today for expert HVAC maintenance services.
