Should Furnace Fan Be On Or Auto In Winter

By - Ron Singh

Updated -

People that live in cold climates will appreciate the work of a furnace. Setting the furnace fan on auto or winter is a common question for house owners.

Running the furnace fan on both settings has disadvantages and advantages, which you should consider before choosing the one you want.   

Your fan should be on the “auto” setting during winter. Unfortunately, furnace fans set on “auto” will only start working when the thermostat tells it to work. Fortunately, it aids comfortability and helps to save time, cost, and energy. In addition, the “auto” setting will help keep the home’s temperature optimal. 

 How Many Hours Should the Furnace Run in Winter?  

Should Furnace Fan Be On or Auto in Winter

No standard number of hours is required for a furnace to run during winter. Typically, a furnace should run for 15 minutes per cycle. It means that a furnace should be able to run 3 to 4 times an hour.

However, your furnace may experience short cycling. Short cycling is when the furnace does not run up to the number of hours it is supposed to run.

As a result, the furnace cannot create the heat needed to warm the house. In some worst cases, the furnace cannot produce any heat.

It would be best if you avoided short cycling by the furnace. It can cause a lot of reversible and irreversible damage to the furnace.

Firstly, the furnace cannot provide the heat needed due to overheating. Also, significant components of the furnace, such as the thermostat, can be damaged, and the furnace itself might need replacement.

Most home appliances show signs when they are not under proper working condition or are not working correctly. These signs worsen over time if there is no action.

Below are some of the signs that a furnace is experiencing short cycling:

  • The thermostat produces inaccurate readings
  • The area around the furnace has more heat and becomes overheated than other areas 
  • There is a production of a small quantity of heat from the air vents

Most of these signs result from abnormalities with one or more of the furnace’s components.

Below are some of the causes of a furnace experiencing short cycles:

  • Bad flame sensor
  • Dirty air vents
  • Dirty air filter

Prevention is better than cure. It is better to prevent short cycling from happening than to start looking for ways to fix the problem when it has started.

However, you should occasionally pay attention to your furnace if it is experiencing abnormalities to find a solution immediately.

Also, check if the air vents and filters are not blocked or dirty. If you notice any dirt, it would be best to clean it off immediately so it won’t block the vents.

Check the flame sensor if it has not gotten rusted. A bad flame sensor is one of the major causes of short cycling.

Also, check the thermostat and pay close attention to know if there are fluctuations in the temperature of the heat produced.

How Do I Prepare My Furnace for Winter?            

Before winter comes, it is good to ensure that you are sure that your furnace is working well.

You don’t want to feel cold and then see that the furnace is not turning on or refusing to work well.

Therefore, preparing your furnace for winter is essential; adequate preparation will prevent avoidable problems when using the furnace.

Most people call a professional to check the furnace and repair any malfunctioning. The major components, such as the flame sensor and filters, are the major check.

However, before the heating, ventilation, air conditioning, and refrigeration (HVACR) professional comes, you can do some checks yourself.

Below are some of the steps to prepare the furnace for winter:

  • Clean the furnace with a soft dry cloth. Remove the items placed on it or close to it. Remove any flammable item close to it.
  • Check and change the air filters if need be. A thorough check will determine if the filter needs to be changed. Filter with dirt should be appropriately cleaned and returned to its appropriate place. You can get cheaper filters during summer because there is little or no demand for them.
  • Clean the air vents. Ensure that any accumulated dust or dirt over time and the vents are clean.
  • It would be best if you filled up gas furnaces. The gas company ensures that the furnace gas is full and there is no leakage. You can get the gas a few months into winter because they are cheaper during that period.
  • If your furnace has a hot water radiator, ensure you bleed the valves. It is to ensure that the air trapped goes out. To do this, slightly open the radiator valves and close the valves when water starts to come out.
  • Finally, test the furnace. The last thing you will want to happen on the first day of winter is for your furnace not to work. If it works well, there is no problem. If it does not, you might need the presence of a professional. Overheating and production of any abnormal sound should be checked and corrected.

During winter, there are some factors you should put into consideration. One of such factors is knowing when to change the thermostat’s settings to suit the home’s condition.

Below are significant rules to ensure your house stays at the average temperature.

Number of People at HomeTemperature 
One person68-69 degrees Fahrenheit
None 65 degrees Fahrenheit 

Is It Better to Leave the Furnace Fan On?        

Leaving the furnace on depends on the preference of the house owners.

Leaving the furnace on means that regardless of the house’s temperature, the furnace will work throughout the day except it is off.

There are advantages and disadvantages of leaving the furnace. 

#1. Advantages of Leaving the Furnace On    

  1. It ensures proper circulation of air. As a result, there is balance in the heating and cooling system in the room.
  2. The furnace will last longer because there is no wear or tear due to frequent turns on and off. 

#2. Disadvantages of Leaving the Furnace On    

  1. It increases the cost of running the home
  2. The furnace filters will accumulate dust faster due to consistent usage

How Much Does It Cost to Run a Furnace Fan in Winter?    

Running a furnace fan in winter every day will cost about $1.15. It may cost a little more than that sometimes.

For about a year, that is about $420. If the furnace fan is on the auto setting, the fan will spend about 12 hours a day running, and the fan will be off for the remaining 12 hours. 

The cost of running the furnace fan in a year will be around $200, slightly above half the cost of leaving the furnace in auto.

Does Running a Furnace Fan Help With Humidity in Winter?  

Running the furnace fan helps with humidity. There is improved air circulation because the furnace fan helps bring fresh air to replace the heat in the house.

The fresh air coming into the house will reduce the humidity levels. Due to the constant running of the furnace, the furnace releases more moisture because of the air going through the furnace evaporator.

Therefore, it will increase the humidity level in the home. However, constant running of the furnace can be dangerous to the system.


Running the furnace fan on auto or leaving it on depends on many factors. However, the eventual conclusion depends on the preference of the house owners and the cost of living.

It is advisable to keep the fan on auto because of its different advantages, significantly reducing the cost of living.

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