This is a common question that many HVAC technicians have been asked over the years. People wonder if there are any advantages or disadvantages to keeping their furnace fan in the “On” position. Many people think that a constantly running fan is a sign that the furnace is faulty and a repair is needed. There are a lot of myths surrounding this subject, and we will attempt to dispel them in this article.
What is the Furnace Fan?
The furnace fan is also known as the blower, and these are interchangeable terms that you may hear when you deal with an HVAC professional. This fan is a critical component that’s designed to push the treated air into and throughout the home. Most modern HVAC systems work with a forced air system. For this system to work, there must be adequate airflow and it needs to be moving in a specific direction. The furnace fan is the most efficient way to get the air moving to heat your home.
Most furnace fans have a small motor rated at 1 hp (horsepower) or less to drive the fan. The size of the motor that you have will depend on the size of your furnace. But, there are situations when the motor size is matched to the square footage of the space that requires heating. This will also include other factors including the number of vents or other openings in the home. Many modern furnace fans can move 1,200 rpm (revolutions per minute), but some models spin at a lower speed. The maximum speed for most residential furnace fans is 1,500 rpm.
Why is My Furnace Run Constantly Running?
The most common cause of a constantly running furnace fan is the settings on the thermostat. Most thermostats have two clear settings, they are: “On” and “Auto” and they work in different ways. The “On” setting forces the furnace fan to work constantly without any interruptions. The “Auto” setting tells the furnace to turn on when the system needs to circulate the treated air through your home. But, if you have a furnace fan that will not stop spinning, the cause may be a defective fan limit switch or it may be on the manual override setting. This problem should be fixed by your local HVAC technician.
Why Would I Run My Furnace Fan Constantly?
We have been conditioned to believe that any device that consumes energy must be turned off to help the environment. Most of the time this is a legitimate concern, but there are times when it’s unavoidable or even desirable. If you run your furnace fan constantly, it’s isn’t necessarily bad and the fan is designed to run constantly anyway. In fact, there are four tangible benefits when you run your furnace fan continuously, they are:
1. Improved Air Circulation
Hot air is lighter than cold air and tends to rise naturally to fill the spaces in the ceilings and attics. The cold air sinks down in the ground and this is known as the “stack effect”. This is a similar principle as a fireplace that draws hot smoke up and out of the chimney. For this reason, most homes have basements that always feel cold when the upper floors are warmer. Your HVAC system can help to balance out these two opposites when treated air (warm or cool) is moved throughout the home. This is less effective when the furnace fan is running intermittently, and you may still notice warm or cold spots. If the furnace fan is running continuously, the temperatures are evenly distributed for a more comfortable home.
2. Lower Energy Bills
The latest energy efficient furnaces have a variable speed furnace fan motor that is actually designed to run continuously. The best known examples are the Energy Star furnaces that are built to meet very strict EPA guidelines. These furnaces will consume less energy, even though the fan is running non-stop reducing your utility bills. As an added advantage, an energy-efficient furnace is kinder to the environment and may have enhanced safety features. If your furnace is reaching the end of its useful lifespan, investing in a new energy-efficient unit makes good financial sense.
3. A Longer Useful Lifespan
Some homeowners believe that they will lower the life expectancy of their furnace if they run the fan non-stop. This is incorrect, the latest models are designed to run continuously and even older models are not adversely affected. In fact, if you run the furnace fan non-stop, it can even help to extend the lifespan of an older HVAC system. The most stress is placed on the furnace fan motor when it’s started up and that is when failures are more likely. But, if the fan is continuously running this is not a problem, and the motor is protected.
4. Better Indoor Air Quality (IAQ)
When the furnace fan is running non-stop, more air is circulating and this improves the IAQ. This is even more noticeable if you have a UV-light purifier or a high-efficiency filter installed. The air will feel fresher and you may notice less dust in your home. During the colder months, the constantly running fan can help to reduce the humidity levels too.
Why Would I Avoid Running My Furnace Fan Constantly?
There are some scenarios where you may not want to run your furnace fan constantly. During the summer, the temperatures can reach up to 140º in an attic and the ductwork can only handle so much. Even high levels of insulation cannot reduce severe levels of heat, and running the fan will pull that hot air into your home. This will make your AC work harder to compensate, extra strain can lead to a failure and higher energy bills. Another potential issue is leaky ductwork, which releases treated air into the attic and crawl spaces with no discernible benefit for your indoor comfort.
If you want to run your furnace fan continuously, contact your local HVAC specialist to get your ductwork inspected, repaired, and cleaned for maximum heating benefits.