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Should I Run My Furnace Fan All the Time?

Furnace interior

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.

Are you in Central Kentucky? Call us at 859-687-0553 – we’d love to chat with you about your furnace needs.

What are the benefits of running my furnace fan?

  1. Better circulation of heated and cooled air
  2. Lower your utility bills
  3. Extend the life of your unit
  4. Improve air quality

Better circulation of your heated & cooled air

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. 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. In milder months, it may only run for a few minutes every hour. 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.

House Diagram

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. The evening sun will do the reverse in the afternoon. Running your furnace fan will blend the air throughout the day keeping the air in your home from having noticeable hot and cold spots.

Is a single speed or variable speed fan better?

Having an ENERGY STAR rated furnace with a variable speed motor is ideal. 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. This ultimately saves homeowners money while also making them more comfortable.

What Size Furnace Do I Need?

We can calculate the correct size furnace for your home. The number of BTUs, or British Thermal Units, needed to heat your home is dependent on a number of variables. Contrary to what you might think, a bigger furnace may not necessarily mean more heating power for your home. If you are in Central Kentucky, call us at 859-687-0553 to get a free appointment to calculate the furnace size you might need.


Lower your Utility Bills

If you have a newer ENERGY STAR rated furnace it will have a variable speed motor that is designed to run all the time. With 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.

Running your furnace fan all the time could save you money each month because having more even temperatures in the home results 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.

Extend the Life of your Unit

Many people are under the assumption that running their furnace fan all the time will cause it to fail prematurely. Actually, the opposite is true. 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.

Air Conditioning

Improve Air Quality

By running the furnace fan all the time, you are also running air through your furnace filter constantly. 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.

  1. If it is the dead of summer and you have ductwork in your attic, temperatures can reach as high as 140 degrees. Even if your ductwork is insulated, it only does so much good against those kinds of temperatures. Running the fan when the air conditioner is not on could actually pull the heat out of the attic into the home.
  2. If you have leaky ductwork. Homes built after 2015 are required to have all ductwork sealed and tested for airtightness. 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.

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!

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