Gas FurnaceOctober 1, 2019by elink18Should I Run My Furnace Fan All the Time?

I constantly get this question from homeowners in the greater Lexington, KY, area, and the answer is almost always, “Yes!” Almost — but more about that later.

What are the benefits of running my furnace fan?

The benefit to running the furnace all the time is better circulation of your home’s heated or cooled air. This is especially true for larger homes or multi-story homes. If you have a two or three-story home with a large staircase, Mother Nature is going to try and heat the upstairs and cool the downstairs, and obviously, we want our home to be the same temperature in every room.

Combating the stack effect & keeping your home comfortable

Because hot air is lighter than cold air, hot air will naturally rise and cold air will naturally fall. In a closed space like your home this process is called the “stack effect” — it is the same process that allows your fireplace to draw smoke out of the chimney. In fact, a large staircase can easily be compared to a chimney pulling all of the hot air in the home to the upper floor, allowing cold air to fall to the lower floor. This is why in some houses the basement is always cold and the upstairs is always warmer.

Your home’s heating and cooling system will help to balance these issues but it does not run all the time and in milder months in may only run for a few minutes every hour. This is where running the furnace fan all the time can help by constantly pulling the cold air from the lower level and warmer air from the upper level, blending the two, and then redistributing a more stable, even temperature throughout the home.

What if I have a single story home — should I still run my fan?

Even if you have a single story home, you should still run your furnace fan. This is because different parts of your home will experience different external temperatures throughout the day.

For example, if your house faces east then the morning sun will likely warm the front rooms of your home a few degrees warmer than the rear of your home, and the evening sun will do the reverse in the afternoon. Running your furnace fan will bend the air throughout the day keeping the air in your home from having noticeable hot and cold spots.

Won’t running my furnace fan all the time raise my electricity bill?

While running your furnace fall all the time might raise your electricity bill a little bit, in the long-term it might even make it go down.

How is that possible?

Well, if you have a newer ENERGY STAR rated furnace it will have a variable speed motor that is designed to run all the time and with our electricity rates in central Kentucky it will cost the average homeowner less than $3 per month to run the fan 24 hours a day. If you have a builder’s grade or older system then it may cost you as much as $10-$12 a month.

However, running your furnace fan all the time could save you money each month because having more even temperatures in the home could result in the heat or air conditioner running less. Since the fan uses much less power than the outdoor unit you save money in the end.

Won’t running my furnace fan all the time cause it to fail prematurely?

Absolutely not. These fan systems were designed to run all the time and assuming your system is properly installed with the correct size ductwork it may even extend the life of the fan. The most stressful part of any motor’s life is that when it starts it is much easier on the motor to run constantly than to start and stop all the time.

Additional benefits of running a furnace fan constantly

By running the furnace fan all the time, you are also running air through your furnace filter constantly, so if you have an efficient filter and a UV light, you are constantly filtering and cleaning the air. This results in healthier indoor air quality for your family and less dust on your furniture.
In the cooling season running the furnace fan can help lower humidity in your home by running air through your air conditioner’s evaporator more consistently which allows the system to pull out even more moisture over time.

When is running my furnace fan all the time not a good idea?

There are a couple of reasons why you may not want to run your fan. The first is if you have ductwork in your attic and if in the dead of summer your attic can reach temperatures of as much as 140 degrees. Even if your ductwork is insulated it only does so much good against those kinds of temperatures, so running the fan when the air conditioner is not on could actually pull the heat out of the attic into the home — and obviously that would be counterproductive.

The other situation that may make running the furnace fan a bad idea is if you have leaky ductwork. Homes built after 2015 are required to have all ductwork sealed and tested for airtightness. However, unfortunately, homes built before 2015 may have very leaky ducts. In fact, according to a study by the Kentucky Department of Energy (DEDI) homes with ductwork in the attic or crawl space in Kentucky had an average of 44 percent leakage! That means over 20 percent of the air in your home is passing through your attic or crawl space before it gets to you — YUCK! If you have an older home with a lot of duct leakage it may not be a good idea to run the fan all the time as it may draw in dirty air from places you don’t want. This can easily be fixed by having a good air conditioning contractor come in and seal your ductwork — it’s not very expensive and is usually done in less than a day.

In short, for most of us running the fan all the time is a good idea. If you don’t have an ENERGY STAR rated furnace make sure the next one you buy is and has a variable speed motor. In my opinion, the government should mandate all new furnaces have a variable speed motor. It’s not a very expensive upgrade and it makes both heating and cooling more efficient which ultimately saves homeowners money while also making them more comfortable. When shopping for your next heating or cooling system this should not even be an option.

If you have an older home you should have your ducts sealed even if you are not planning to replace any equipment anytime soon. If you do have equipment replaced, make sure your contractor adds duct sealing to the job. Also adding indoor air quality products like high-efficiency filters or ultraviolet light systems will greatly improve the air in your home while running the furnace fan, so that you can turn your furnace into a whole-house air cleaner!

Contact Synergy Home today at 859-687-0553 or request service online for information on these or any other heating and cooling issues.


  • Gordon

    October 24, 2019 at 12:50 am

    Very informative.


  • Brenda F

    November 14, 2019 at 4:55 am

    Thank you. Very informative. We just had a furnace contractor tell us to leave our furnace fan on continuously to even out the heat in the house. So far we are feeling more even heat in the rooms. My question is, how do we know if we have duct leakage if our condo is built on a slab? The ductwork is not vented in the attic and we do have a high efficiency electronic air filter on the furnace.


    • Cindy Isaacs

      July 9, 2020 at 4:28 pm

      The greater question is if you have duct work running through the concrete slab, you should have a radon test completed to ensure it is not pulling radon from the ground. If you are in a condo you might want to run your furnace fan only during peak heating and cooling hours. If you are located near Lexington, KY, and you’d like us to do a free site visit to give you advice, we’re happy to do so.


  • Cindy

    November 22, 2019 at 1:48 am

    Very informative, thank you for all the information!


  • Paul Patterson

    December 5, 2019 at 6:52 pm

    Hi, can you advise if you can operate the automatic fan on an oil fired furnace at the same time turning up the thermostat to bring heat on through via the fan?


    • Cindy Isaacs

      July 9, 2020 at 4:30 pm

      Yes. The heating needs of the fan will always override the constant fan setting.


  • Paula

    December 21, 2019 at 1:28 pm

    I have a single story home with vaulted ceilings and a new furnace in the attic. Should I run the furnace fan all the time?


    • Cindy Isaacs

      July 9, 2020 at 4:31 pm

      No, we do not recommend constantly running the furnace fan in the heat of the summer, as you will draw attic temperatures into the living space. The rest of they year, you should be fine, but please use your best judgement.


  • Aformations

    March 12, 2020 at 5:51 pm

    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.


    • Cindy Isaacs

      July 9, 2020 at 4:33 pm

      Yes, this is a good feature for individuals who do not want to run the fan constantly, but still want to have some air circulation.


  • John D Umbower

    April 11, 2020 at 3:17 am

    Finally someone who knows what they’re talking about! Perfect sense⚡️


  • Marcus

    May 11, 2020 at 2:58 pm

    I run my furnace fan continuously at LOW speed. But I’m not 100% sure what speed it should be at. Also, should I run the humidifier with the fan or just when it calls for heat?


    • Cindy Isaacs

      July 13, 2020 at 1:22 pm

      When running your fan continuously, we recommend doing so on the low speed setting. You should only run the humidifier when it calls for heat.


  • Jim

    May 23, 2020 at 6:44 pm

    I have an old stone wall basement with a drylock sealed cement floor. It has moisture but is always around 55°. My older oil furnace does not have A/C . I would like to use the fan with a high quality air filter and mix the cool basement air with the warm air of the second story bedrooms and hallway. I have a nice dehumidifer I will run also. Not sure if the furnace fan will do ok without an A/C unit.


    • Cindy Isaacs

      July 9, 2020 at 4:24 pm

      There is an option to use the cold air from the basement to temper the air upstairs. Modern furnaces are designed to do this using very low energy, however your older oil furnace may use more energy, so it may be more trouble than it’s worth. We’d be happy to provide a free estimate on a modern furnace that would be dramatically more efficient than what you have.


  • Architects in Dublin

    August 4, 2020 at 3:17 pm

    Will definitely make use of a few of these techniques
    on some of my upcoming projects. Cheers for the great share.


  • Stacie

    August 6, 2020 at 7:38 pm

    Hi I live in New England and it’s summertime I have a brand new HVAC with an HRV if I continuously run the fan in my home during the cooling season it just drives the humidity up in the home from the condensation in the evap coil drip pan doesn’t make sense to keep it off in my case?


    • Amy McSharry

      August 7, 2020 at 6:07 pm

      Without me knowing the exact set up of your system, it would be hard to say why you are seeing increased humidity. We recommend checking back with your installing contractor.


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