Both inline and axial fans can move air, but they differ in their operation, performance, and the one that you should use. This guide takes you through those differences.
What is Inline Fan?
An inline fan is installed within a duct or a pipe and forces air through the length of the duct.
What is Axial Fan?
Axial fan is a fan that utilizes propeller-like blades rotating around a central hub to push air directly through the fan.
Key Differences Between Inline and Axial Fans
a) Design and Mechanical Operation
Inline fans incorporate centrifugal or mixed-flow impellers encased within a cylindrical housing. In centrifugal design, the fan blades suck air in and eject it at 90 degrees to the inlet, thus producing a higher pressure.
Mixed-flow fans use both the axial and centrifugal concepts where air moves diagonally through the fan. They are small and cylindrical in shape and can fit directly into ducts to maintain streamlined flow of air.
Conversely, axial fans utilize propeller-like blades attached to a hub. The fan blades spin around the axis of the fan, moving air parallel to the axis. This design is less complex, lighter and suited for moving large amounts of air at low pressure.
b) Airflow Direction
In inline fans, the air is forced through ducts in a linear direction or with some slight curvature in mixed flow relative to the body of the fan. They push air in and through ductwork, keeping resistance in consideration.
Axial fans pull the air through one side and push it through the other, along the same direction as the shaft. Airflow is linear and direct.
Since the axial airflow is always parallel, these fans are most effective in open areas or short ducts without obstruction. In longer and complex ducts, inline fans are more effective in handling resistance.
c) Installation Method
Inline fans are fitted within ductwork. They fit between duct sections or are attached by flanges. Since they are in line, airflow remains enclosed and directed.
Axial fans are commonly mounted in vents, walls, or duct ends. You may find them in window units, wall exhaust vents, or even outdoor environments.
d) Pressure and Efficiency
The inline fans, particularly centrifugal fans, produce more static pressure. They are capable of forcing air through filters, bends, and long ducts. They are designed to withstand resistance.
Axial fans provide high volume but low pressure. They are most effective when the resistance is low. Their performance decreases as the duct length or obstacles increase.
Inline fans are also efficient in dealing with resistance. They sustain flow where axial fans would struggle. Axial fans, however, move air more easily in open spaces where resistance is minimal.
e) Noise Levels
Inline fans are generally quieter, particularly when they are installed in ducts. Duct walls help absorb sound. The design of their blades is also intended to minimize turbulence in ducts.
Conversely, axial fans are more exposed. Air flows through blades creating turbulence and noise. Larger diameters and lower speeds will be useful in reducing noise, but in most instances axial units will still produce an audible hum.
The axial fans are noisy due to vibrations and turbulence when they are mounted without damping or when the surrounding environment responds to sound.
f) Maintenance Requirements
Inline fans are installed within the ducts and therefore reaching them might involve the removal of duct sections or panels. Once accessed, it now becomes easier to clean blades, inspect bearings, and operation of the motor.
Axial fans are usually exposed and therefore easier to clean. You are able to clean blades, check supports and lubricate in a matter of seconds. Since they are simple in design, parts are likely to last longer without complicated wear points.
g) Cost
Buying Cost
Axial fans cost less up front. Their simple design and smaller housings reduce the cost of materials and production.
Conversely, inline fans are more expensive due to the extra housing, complicated impellers and structural reinforcement to sustain duct integrity.
Operating Cost
Under resistance, axial fans become inefficient and consume more energy in ducted systems. In the long run, that increases your bills. In natural duct conditions, inline fans have a more stable operation, thereby reducing energy wastage.
h) Energy Use
Axial fans use more energy to move large volumes of air. They operate effectively when resistance is minimal. However, in ducts, or tight spaces they waste energy in trying to overcome pressure.
In ducted systems, inline fans are more energy efficient. Their curved blades and shape assist in minimizing energy loss and ensuring a consistent airflow.
Inline fans using EC (electrically commutated) motors are generally more efficient. They automatically adjust their speed and consume less power when operating at reduced capacity.
When to Choose Between Inline and Axial Fan
- An axial fan is used when you need to move large volumes of air in open spaces with minimal ducting or reduced resistance.
- Use inline fan when there is a need to move air through ducts, bends, filters or long runs.
- In case of noise, an inline fan offers a less noisy option.
- An inline fan is more efficient in long-term energy saving in ducted systems.
Here is a summary of the selection criteria:
| Conditions | Inline Fan | Axial Fan |
| Long ducts (When there is air resistance) | Recommended | Not suitable |
| Area of installation | Within the duct system | On wall surfaces, windows or any opening that is strategic |
| Noise level | Low | High |
| Maintenance | Difficult since you have to access the duct system | Exposed hence, easier to access |
Conclusion
Both inline and axial fans satisfy airflow requirements. Inline fans are more efficient in handling pressure and resistance whereas axial fans move large volumes of air at low pressure. Thus, your selection should be aligned with your requirements in terms of system, noise, cost, and layout.
FAQs
Which fan type is easier to maintain and clean; inline or axial?
Axial fans are open and have a simple design, and therefore it is easier to clean and inspect them. Inline fans need duct access to be cleaned and thus cleaning becomes a little bit difficult.
What are disadvantages of axial fans?
Axial fans face problems with ducted systems, are less effective under resistance, and tend to be noisier.
What are the disadvantages inline?
Inline fans cost more upfront, must be sealed carefully, and may demand duct modifications during installation.
