How Does an Inline Fan Work?

Inline fans are a great way to bring air from the outside into a building.

But how does an inline fan work? An inline fan is installed to the ductwork of an existing HVAC system. Its purpose is to boost the airflow speed with its powerful motor and blades, so that fresh air can circulate and the pollutants in the air can be extracted more quickly. Depending on your needs and HVAC configuration, you will have to choose between an axial, centrifugal, or mixflow inline fan.

Table of Contents

Types of Inline Fans

Single port and multiport versions of inlet fans are available to accommodate varying needs. Single-port fans have one inlet (incoming) supply duct and one outlet (outgoing) exhaust duct. Multiport versions can be used to ventilate two bathrooms or for larger buildings.

The following types of inline fans cover a range of needs, from residential to commercial. If you’re just looking for a simple inline fan for your residential home, we recommend checking out this one.

Without further ado, the following are the types of inline fans you may encounter:

Axial Inline Fans

These fans are useful in small rooms where the ductwork length is minimal. They allow high extraction at low pressure.

Centrifugal Inline Fans

These fans work efficiently with long ducting, bends in ducting and multiple inlet-outlet settings. They are well suited for large heat transfer and large ventilation settings. Although, you’ll usually find them in large commercial spaces, not residential homes.

Mixflow Inline Fans

They are well suited for medium-sized spaces. They work efficiently with moderate size ducting. Mixflow fans are a combination of axial and centrifugal fans, and thus are suited in rooms that are neither small spaces nor large commercial areas. For example, a small- to medium-sized commercial kitchen might use this kind of fan.

Advantages of Using an Inline Fan

An optimal inline fan setup will allow clean air into an enclosed space from outside while removing the inside air. Here are some advantages of using an inline fan:

Improvement of Air Quality

Inline fans remove stale fumes, smoke and odor from the closed spaces and improve air quality. It allows fresh air to rush into the spaces.

Multiple Intake Points

Multiport versions of inline fans can be used for large-sized spaces requiring multiple ventilation ports.

Remote Installation

Remote installation of inline fans allows for more aesthetically pleasing look for areas where required. It can be used for kitchen hoods and bathrooms.

Noise Reduction

Because the fan is present a little far away from the room or space, it reduces the noise. You can add an inline muffler, rigid ducting or insulation ducting if you want it to be even quieter. Noise reduction clamps can also be used to reduce noise.

Higher Extraction Rates

Likelihood of mould formation is reduced greatly because inline fans very efficiently remove the moisture. They also prevent odours and regulate temperature by constant ventilation.

Inline Fan Installation

The configuration of the arrangement depends on the space you have. If you have a lot of space, you can install fans and filters inside the space. For that, you would need to mount the fan by using clip hangers. But if space is small, install these components outside the space.

The clamps should be used at every junction to secure the connections. Duct tape can be used if needed to prevent air leaks.

What CFM Rating Fan Should You Use?

Inline fans measure their output in CFM. CFM is the measure of the volume of air in cubic feet for each minute it moves. When looking for an inline fan, it is recommended that you pick a model that has a greater CFM rating than the minimum value you calculated. This way, you can run the fan at a lower power setting. It will reduce the noise and also account for future space size changes.

The Calculation for CFM

To find the airflow needed for your space, first, find its volume in cubic feet. Convert the room dimensions from inches to feet. Multiply its length by its width and by its height.

A 5x5x8 small room has a volume of 200 cubic feet. To exchange this tents air once every minute, you would need a fan with a 200 CFM capacity or higher.

However, keep in mind that the length of ducting, any bends in ducting, carbon filters, lighting and silencers can decrease the fan’s output.

You would have to factor all these things and buy a fan with even higher CFM. You can use the estimated efficiency percentages of each of the accessories to factor into CFM calculation.

If the carbon filter has a 50% rating or above, you will multiply the CFM by 1.5. Factor in all the accessories and the new CFM value inline fan will be required to ensure your fan will perform closer to its calculated and listed airflow.