How To Tell Which Way A Fan Blows

Fans are everywhere it seems! They’re critical for everything from cooling a computer’s CPU to keeping us comfortable or even helping with plant grow rooms. It’s honestly amazing how versatile they are.

But do you know how to tell which way a fan blows? If not, I’d love to show you how. Once you’ve got the basics down it’s not hard at all!

In this post, I’ll share with you the details you need to do so. Not only that, I’ll help you better understand how fans work along with sharing some helpful facts to know.

Infographic – Fan facts and airflow basics

How a fan blows and fan facts infographic

How to tell which way a fan blows – 3 basic methods

The great news is that generally speaking it’s easy to tell fan air direction if you know what to look for. Because of how they work (and how most are designed) there are great clues to help.

It also depends strongly on the fan’s intended use as well. Here are 3 ways to tell which way a fan blows:

  1. Using the fan angle and rotation direction
  2. By the type of fan and its intended use
  3. Fan directional markings

1. Fan blade angle and rotation direction

Fan air flow diagram

The direction a fan blows air is always determined by (A) the shape of the blades (sometimes called propellers) and (B) the direction they turn. If a blade is angled down and the fan turns in the same direction as the blade angle, it will blow forward. Likewise, if the blade is angled down and the fan turns the opposite direction, the reverse is true. Air will blow in the other direction (towards the back).

These two characteristics of a fan are probably the easiest and most common way to tell which way it blows.

That’s because a fan always has the same basic design in one form or another: fans use angled and slightly curved blades to cut through the air and force it forward or backward depending on the direction of rotation.

Here’s an animated image I’ve put together to help show this.

In this image you can see exactly what I’m describing: the fan is rotating in the same direction as its blades which are angled downwards. This causes air to blow upwards (to the front of it).

If the fan’s direction is reversed, the air will go the opposite direction as it would be forced downward (towards the rear) instead of the front.

An everyday example

CPU fan air flow direction example illustrated

Here’s a great example of how to decide which way a fan blows. This is a common small fan powered by direct current (DC) and used for many electronics cooling applications. Looking at the fan, we can see the angle of the blades and we know that most of these rotate clockwise (the same direction as a clock). Therefore, unless the power polarity is reversed, it will blow air forward.

The image above is a great example of a common fan you might run across. By looking at the fan and knowing which way the blades are angled, and knowing that it normally turns clockwise, I can see that it will blow air forward.

Of course, if for some reason the fan rotates in the opposite direction (unbeknownst to me) the air would be blown the other way.

2. The type of fan and its intended use

centrifugal fan vs axial fan comparison diagram

Fans generally only come in a few basic designs, most of which are axial or centrifugal types. Centrifugal fans normally only blow in the direction of the outlet as shown, while axial fans may be reversible in some cases. 

While many variations of fans exist, nearly all fall into just a few basic categories as the most important design principles are the same.

A fan’s direction is often fixed and largely determined by what it was designed to do:

  • Airplane propellers and jet engines always force air from the front to the rear
  • Ceiling fans are normally used for blowing air downwards into the room but can be reversed to force air to the ceiling
  • High-speed cooling fans of the centrifugal type blow forward
  • Home cooling fans normally blow forward and can’t be changed
  • Ventilation fans are mounted in a wall, window, or other assembly and spin to blow air out of a building

Lasko 3720 Weather Shield box fan in window

Most common home fans used for cooling like this Lasko 3720 window box fan are designed to blow only one direction: forward. You can see the blade shape in the picture which gives a clue about this as well. You’ll need to rotate the fan 180° to change the air direction.

Fans powered by alternating current (AC) such as common household 120V or 220V fans typically can only blow forward. However, direct current (DC) fans are often reversible.

That’s because DC power can change the operation of the electric motor inside the fan, causing the blades to spin in the opposite direction and force air to the rear.

3. Fans that have directional markings

Illustrated image of computer fan air flow direction

An example of some common fans with markings to show which way air blows. In both cases, there are 2 arrows: one to show the direction of rotation, and one to show the airflow direction. Left: This fan is the most common type, as it can be mounted backward if you need to reverse airflow. Right: This fan is less common but does have some uses where the airflow going to the rear is important.

While it’s not as common, some fans do have a marking indicating which way they blow. If you’re lucky enough to find that on one, it makes it even easier to tell!

Ordinarily, you’ll most likely find this on general-purpose fans like small DC powered fans for electronics cooling. However, from time to time it can be found on others.

It’s really handy to remember method #1 above. That way you can tell which way a fan blows nearly 100% of the time and especially if one isn’t marked with arrows or a label to tell you.

Did you know? Great fan facts

Fans are typically not very expensive but can be very cost-effective in many applications. They’re helpful for many common uses and problems, but there are some things you might not know about them.

Here are some great fan facts to know. Be sure you’re using fans to improve your quality of life (and save money) as much as possible!

1. They’re very energy-efficient vs. air conditioning

Tower fan money saving badge imageElectric fans can run and help cool you and your room with up to an amazing 60% less power than air conditioning units!

That’s because fans don’t need nearly as much electric current to work. Air conditioning (AC) units not only have to power an electric fan but also an energy-thirsty refrigerant compressor motor. That adds up over time!

2. Fans cool you…but don’t actually cool the air!

Fan cooling forced convection diagram image

Fans can make you feel cool and comfortable as well as cycling the room’s air to prevent heat from building up. But did you know? They don’t work by chilling the air. They work off of the principle known as forced convection.

Here’s a cool (no pun intended!) fact – electric fans don’t cool a room by dropping the temperature. Air conditioning units do so by removing heat from the air.

Fans create a cooling effect by the principle known as forced convection. That just means that fans cool your body and your room by forcing air across surfaces, removing heat from you into the nearby air.

They also keep air circulating within a room, offering a continual effect that makes you more comfortable.

Because of that, it’s important to have a well-designed fan with great airflow and especially one with an oscillation feature to move back and forth, covering a large area in a room.

Lasko T42950 Wind Curve tower fan example

Tower fans are specially designed to produce a comfortable airflow. They’re different from other types as they produce a tall, vertical area of air and often oscillate (move side to side) to cool a room.

Tower fans like the popular Lasko Wind Curve at Amazon are an excellent example of this.

3. They’re great for white noise

Lasko 3720 Weather Shield box fan front image

A simple but classic box fan like this popular Lasko 3720 model produces a soothing and calming “white noise” that can improve your quality of life. A side effect of how they work, the noise “masks” (covers up) outside noises like your neighbors, traffic, people talking, and more. It’s a great and cost-effective way to help you focus, relax, or sleep better.

Fans are also very helpful in some cases for blocking outside noises that cause us stress and interrupt sleep, studying, or working.

Models that produce a very high airflow rate and introduce a lot of turbulence near them as a side effect can produce a large amount of soothing white noise. Box fans are especially helpful for this.

If you’re interested in finding out more, here’s a great post with some of the best box fans for white noise you can buy.


Being able to tell which way a fan blows isn’t difficult in most cases. Just remember these basic tips:

  1. Look for directional arrows
  2. The power source type (AC or DC) and intended use
  3. You can nearly always tell from the blade angle and rotation

Do you have suggestions, more questions, or wish I covered some topics in more detail? Feel free to drop a comment below or reach out to me.

Additional reading

Want to know how much energy a fan can save? Find out how much electricity an air conditioner uses vs a fan here.

Need to cool out? Here’s a helpful post with some of the best tower fans you’ll find today.

Your comments are welcome!

  1. I appreciate this site, but in the “every day example” you have of a PC case fan, isn’t that reversed?
    If it’s moving clockwise, wouldn’t the air move from the front of the fan to the back (in this picture) since the blades would “‘scoop” the air from the front?
    If not, I’m thoroughly confused.

    • Hi Don. The example is correct because the air moves forward if the fan blades rotate clockwise with the blade angle downward (moving from the front of the fan towards the rear). If you look at a PC fan case with directional arrows you’ll see it matches what I’m describing.

      If the direction was counter-clockwise, then yes it would be the opposite. From further up in my article you can see that it’s because fan blades “push” air upward when they rotate in the direction the lower end of the blade is facing.

      Thanks for visiting. :)

  2. Hello,

    I just came across your site and appreciate the site also and wanted to ask a question. Do they make a fan (like the Centrifugal) that blows downward and the intake is from the side, not the top? I thought laptops had that type fan.

    • Hi Bobby and thanks for dropping by. I think the type of fan called a “centrifugal inline duct fan” would be the closest to what you’re describing. I didn’t have any luck finding anything besides that.

      The fans that I’ve seen in laptops so far resemble a traditional centrifugal fan.

  3. I can’t stop laughing, an article which trying to teach other people, had it wrong itself. look at the “An everyday example” picture, the rotation direction and airflow direction are all wrong, the rule is very simple, the side with plastic bars connecting the motor to the frame, is the side where the air comes out.

    • Hello Tony. Although your comment was rude and misplaced I’d like to respond in order to clear up your misconceptions.

      The example shown most certainly is correct. In fact, I personally verified the information and examples in this article with actual fans rather than make assumptions as you did in your comment.

      Fan airflow, as I stated in the article, always depends on the particular fan and is based on 2 things:

      1. The direction of rotation
      2. The angle of the fan blades

      There’s no kind of assumption to be made in many cases like “the side with plastic bars connecting the motor to the frame” as this is incorrect. Common PC case (and other) fans are not standardized. The airflow depends on the design of the fan but will always follow the 2 rules above, guaranteed.

      If a fan has its voltage reversed or is designed to rotate in the other direction then yes, the airflow can be reversed. Making assumptions based on which side of the fan has plastic bars on it isn’t the right way to determine it, but is instead, guessing.

      Have a good day and thanks for dropping by.

  4. Grant
    Great article. I enjoyed the read. I apologize for some of the rude comments. The way I think of this is to ask the question as to what is the leading edge of the blade as it rotates? Airflow will always flow from leading edge to trailing, just like the wing on an airplane.



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