Is It Bad To Run My Furnace Fan All The Time?


Circulating Air with Furnace Fan

Most thermostats today come with an option to keep the furnace blower fan running continuously. But is it a good option for circulating air in a house and can it help redistribute air and reduce reliance on a furnace or A/C system?

Running a fan for circulation requires looking at multiple factors including the weather, the age of the HVAC system, the home, and the people living in it. If it’s very hot or very cold outside, it doesn’t make sense to run the fan constantly because most newer homes, and almost all homes we install replacement systems in, have a fresh air intake (aka make-up air) that is tied into the ductwork. Whenever the fan runs, some ambient exterior air (hot/humid/cold/dry) will be mixed into the circulating air in your system. This air will need to be conditioned (heated or cooled), so you could be creating more work for your air conditioner or furnace by running the fan continuously in a hot/cold situation.

In some cases, this can result in the system not being able to keep up during the hot/cold extremes. Also, during these extreme temperatures, the furnace and AC are already running more frequently, so air is being regularly circulated.

Mild Temperatures Can Be Optimal For Fan Usage

When the temperatures are more mild outside, a whole home HVAC system might not turn on often enough to keep a balanced temperature in the home. So generally speaking, it makes sense to run the fan constantly, or use the circulate option on a thermostat, if there is minimal heating/cooling taking place and you aren’t opening the windows for ventilation or air movement.

The circulate feature on some thermostats will automatically run the fan for around 20 minutes out of every hour. This helps circulate the air and maintain a more balanced temperature without having to run the fan continuously.

Age of System – The age of an HVAC is important because new furnace systems have make-up air intakes that can cause your system to run more frequently even though you are simply looking to circulate air in the home. Most make-up air comes through a PVC intake pipe routed to the exterior of the home at grade.

Lifestyle – Some people are sensitive to outside air and aren’t able to open windows. A continuous fan can help keep a home comfortable in mild temperatures and reduce the requirement to ventilate with windows.

Home – Each house can have its own particular situation. Maybe your baby’s room is at the end of a long heating run and by running your fan, you are hoping for more air to circulate through their room. There might be other options for correcting uneven heating, but running a fan might solve this in the short term. We often see major differences in temperature balance for 2 or 3 story homes whereas a ranch home is easier to keep a stable temperature. Using a whole house HVAC fan to help balance temperatures can help in these situations.

Circulating Thermostats

Thermostats with a circulating option are becoming more common on the market. Here are a few of our favorite that offer a programmable circulate mode for the HVAC fan:

  1. Honeywell T6
  2. Honeywell T6 Lyric WiFi
  3. Honeywell VisionPro 8000 WiFi
  4. Honeywell 9000 WiFi
  5. Aprilaire 8400 Series
  6. Bryant Evolution Connex Control


Pharo Heating & Cooling is a full-service HVAC contractor in Madison. Our team provides top quality service for new construction and replacement furnace and air conditioner needs. We work exclusively with Bryant Heating and Cooling products, and all work is done by our own team. For more information about HVAC systems or furnace or AC concerns, give us a call at 608-849-5410 or submit a contact form through our website.

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