Should I Set my HVAC System’s Fan Setting to Auto or On?

The fan setting on your thermostat controls your HVAC’s system blower. The blower helps circulate hot or cold air throughout your home until the temperature on the thermostat is reached. There are two settings on your thermostat to control the fan – auto or on.

AUTO means that the fan turns on automatically only when your system is heating or cooling air. Once the thermostat reaches the desired temperature, the entire system shuts off until the next cycle.
ON means that the fan is constantly on and blowing air when your HVAC system is not heating or cooling air.

Running your fan on AUTO or ON is a personal preference. We’ve provided pros and cons of each setting option, so you can decide which one is best for you.

Pros to setting your thermostat fan setting to AUTO
  1. Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously.
  2. 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. If your fan runs continuously, moisture does not have a chance to drip outside. It blows back into your home and your AC works hard to remove extra moisture from the air.
  3. You’ll need to replace your furnace filter more frequently. Air is continually being cleaned causing filters to get dirty more quickly. A clogged filter also makes your blower work hard and use more energy.
Cons to setting your thermostat fan setting to AUTO
  1. You may notice that there is less even distribution of hot or cool air. Once the air temperature reaches the temperature on your thermostat, the fan stops moving air throughout your home.
  2. The blower motor fan may wear out faster due to more frequent starts and stops.
Pros to setting your thermostat to ON
  1. Allowing the fan to run uninterrupted, there is a more even distribution of warm or cool air circulating through your home. This will help reduce hot or cold spots within your home.
  2. There could be reduced stress on the fan from less frequent starts and stops, which could potentially help extend its lifespan.
  3. The air could be cleaner in your home if it is pulled through a filtration or UV light system.
Cons to setting your thermostat to ON
  1. It may cost your more money to run your fan nonstop. Some systems have blower motors that are designed to run in the ON mode, while others are not rated for continuous use.
  2. In the winter, you may notice cool air coming out of your vents. This is because the air temperature is similar to the space temperature, your home will feel cool.
  3. You’ll need to replace your furnace filter more often as air is constantly being blown through it.
  4. During the summer, any ducts that run in your attic or close to your outside walls can fill with warm air, blowing hot air into your home. Your HVAC system many now need to run more to offset the additional heat.
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