Whenever your air conditioner is running, so is your HVAC fan. But it’s up to you whether the fan should continue to run after your home reaches its target temperature -- and the choice is generally between cost and comfort.
Auto vs. On
Most HVAC systems only have two fan settings: “auto” and “on”. When your thermostat is set to “auto”, the fan will only run simultaneously with the air conditioner to help distribute the cooled air. When it’s set to “on”, forced air will flow from your vents continuously until you change the setting.
The primary benefits to the “auto” setting are that it helps conserve energy and reduce wear and tear on HVAC parts, particularly the fan motor. It may also help you get a little more use out of each HVAC system filter because air doesn’t pass through it at all times. The downside is that your household air will gradually grow stagnant between cooling cycles. If you don’t open the windows during the mild seasons, things could get pretty stuffy before the air conditioner kicks on again.
By using the “on” setting, you’re dealing with the opposite situation. Air is being replaced continuously, so your indoor air will seem fresher and household odors will be less noticeable. Allergy sufferers may especially benefit from this endless circulation. On the other hand, the 24-hour cycle will show up on your monthly energy bill, and your filters will need more frequent replacement. You should also expect more frequent maintenance, repairs, and replacement of the fan motor.
Another potential downside of using the “on” setting is that it can draw humid outdoor air into your home between cooling cycles. If you live in an arid region, this is unlikely to be a concern. But in humid environments, you might want to counteract this effect with whole-home dehumidification if you need the continuous fan to improve indoor air quality.
Need a Compromise?
If you find that you like the benefits of the “on” setting but wish you could reduce the additional operating cost, that’s something to consider when your air conditioner nears the end of its life. Some models are available with variable speed fans that offer greater customization of airflow during cooling cycles and in-between. You can program these units for high fan speeds while the A/C is on and slower speeds when the system is just circulating the air.
To explore variable fan HVAC system options or assess how close your system is to requiring replacement, reach out to your local HVAC technicians today.