Although it may seem simple to install a HEPA air filter, a few small mistakes can affect the filter’s performance.
The filter must be correctly oriented, sit properly in the housing, and have a good seal around the frame. If there is a gap, some air may go around the filter media instead of through it.
The good news is a properly installed HEPA air filter usually takes just a few minutes to install.
In this guide you will learn how to install a HEPA filter in an air purifier, how to check the direction of airflow, how to identify problems with sealing, and when to replace the filter.
How to Install a HEPA Air Filter in an Air Purifier
The installation process is similar for most air purifiers.
Step 1: Switch Off the Air Purifier
Unplug the unit and turn it off before opening the filter compartment.
This gives you a safe start and stops the fan from running while you are removing or installing the filter.
Step 2: Take out the old filter and its packaging
Open the filter housing and take out the old filter.
If the new filter is in a plastic bag, make sure to remove it completely before installing the filter. A filter can’t let air through when it’s still sealed in plastic.
Please check the housing for dust or debris and clean the area if necessary.
Step 3: Check Airflow Direction
On the filter frame, look for an arrow indicating airflow.
Often the arrow shows the direction in which air must be moved through the filter. Do not attempt to determine the direction of the filter placement by looking at the pleats. Use the instructions that come with the filter for installation.
If the filter has multiple layers or is asymmetrically constructed, the arrow is especially important.
Proper Filter Placement Step 4
Place the filter into the housing, making sure it is level on all sides.
Verify that:
- The filter is fully in place
- The frame is on the ground
- The gasket is touching the case
- No corner is raised
- The filter is not slanted
- The housing can close in the normal way
Do not force the filter in. If it doesn’t fit, please verify the dimensions and orientation instead of forcing it against the frame.
Step 5: Shut the housing.
Close the filter cover or access door until it latches.
If the filter is properly seated, the housing should close without unusual resistance.
If the cover fails to close properly, remove the filter and check that it is installed correctly, aligned properly, and the correct size.
How to put in a HEPA filter?
The easiest and safest way to install is to follow the direction arrows on the airflow or the manufacturers instructions.
There is no universal rule that one specific side of every HEPA filter has to be installed facing the same direction.
Filter designs can differ in the manner in which they utilize media structures, support layers, frames, and airflow patterns.
AIR FLOW arrow. If the air handler has an arrow marked AIR FLOW, install the filter with the arrow pointing in the direction of the air flow.
If no arrow, use the manufacturer’s instructions or product documentation, not the way the pleats appear.
What if the filter is installed improperly?
The filter may not work properly or may cause resistance to airflow if it is not oriented correctly.
You might notice:
- Weird fan noise
- Less air flow
- A door on a house that doesn’t shut well
- A filter position that is not even
- air flowing around the frame
These symptoms are not always proof that the filter is backward, but they are good reasons to stop and check the installation.
How to Know if Your HEPA Filter is Installed Properly
When the filter is correctly installed, it should be a snug fit inside the housing, maintaining constant contact around the frame.
Watch for these signs:
- The filter is level.
- Housing closes completely
- The frame does not deform.
- The gasket is always in contact
- No visible gaps around the filter
- The purifier is working fine
Do not depend upon the feel of the air from the outlet. The critical question is whether air is moving through or around the filter media.
What Happens if a HEPA Filter Is Not Sealed Properly?
A HEPA filter is designed to filter air that passes through its filtration media.
If there is a gap between the filter and the housing, some air may take the easy way around the filter.
This is called air bypass.
So the real-world performance of a filtration system is more than just the effectiveness of the filter media. The frame, gasket, housing, size, and installation all matter.
Why Fit Is Important
If the filter is just a little too small, it can leave a gap around the frame.
An oversized filter can cause deformation when installing or prevent the housing from closing properly.
That’s why the proper filter size is important for both replacement products and OEM designs.
Here’s what dimensions, tolerances, gasket positions, and mounting features should be specified before production when designing a custom filter product, according to our OEM filter CAD drawing checklist.
Why the Gasket Is Important
This gasket is the interface between the filter and the housing.
The filter thickness, location, material, and compression can affect the seal.
Even the most efficient media in a filter can lose all practical performance if the surrounding seal is not tight enough to prevent air from bypassing the media.
How Often Should You Change a HEPA Air Filter?
There is no universal replacement interval for air purifiers.
The life of a filter depends on some factors like
- Business Hours
- Indoor particle concentrations
- Room condition
- Animals
- Exposure to smoke
- Filter size
- Filter media
- Air flow
- Dust loading
A manufacturer’s suggested replacement schedule is a good starting point, but you should also consider the condition of the filter.
Signs Your Filter May Need Replacing
Look for:
- Heavy visible dust loading.
- Significantly less air flow
- Growing fan noise
- A filter surface that appears to be heavily loaded
- Replacement indicator on the purifier
- A filter at the manufacturer’s recommended service interval
Just because the calendar says a filter still has time left doesn’t mean you want to keep a dirty filter in service.
HEPA Air Filter Replacement
The replacement filter is installed in the same way as the original.
- Switch off and unplug the air purifier.
- Open filter compartment
- Remove the old one.
- Remove any loose dust from the housing.
- Take the new filter out of the protective packaging.
- Verify the direction of airflow.
- Install the new filter evenly.
- Make sure the gasket is in place.
- Close the housing and secure it in place.
- Switch the purifier on again.
Unsure about orientation? Place the old and new filters side by side. This can help to verify that the housing is oriented correctly before it is closed.
Common Errors in Installing HEPA Filters
A few simple mistakes cause most installation problems.
Do Not Remove Plastic Wrap
It cannot filter the air if it is sealed in plastic packaging.
Remove protective packaging before installation.
Installing the Filter Without Checking the Arrow
Don’t guess at the direction by the looks.
Follow the airflow marking on the unit or the manufacturer’s instructions.
Incorrect Filter Size
If a filter is not a match for the housing, it can cause gaps, deformation, or problems with the installation.
Use the proper model and dimensions of the purifier.
Overlooking the Gasket
The gasket should be flush with the housing.
Any visible gap around the sealing surface will allow air to bypass it.
Forcing the Filter in Place
If the filter does not fit, stop and check the model, dimensions, and orientation.
Forcing the filter can damage the frame or the housing.
Filter Design: Step One in Filter Installation
For end users, proper installation is mostly a matter of following the manufacturer’s instructions.
But for brands and manufacturers, installation performance starts much earlier.
The filter is to be designed around the housing.
This includes:
- General dimensions
- Dimensional tolerances
- Design of frame
- Gasket place
- Features mounting
- Filter thickness
- Airflow Needs
A well designed filter should fit the intended housing consistently across production batches.
For OEM projects, these requirements should be defined prior to tooling and mass production. We also offer OEM and ODM filtration solutions such as filter engineering, customization, sampling, testing, and production for a wide range of applications.
Final Inspection Before Using Your Air Purifier
Wait a few seconds and then turn the unit back on:
- The protective packaging has been taken off
- The airflow is properly directed
- The filter is seated correctly
- The frame is horizontal
- The gasket touches the housing
- The filter compartment closes tight
- No visible gaps around the filter
For a HEPA filter to work properly, it is necessary to correctly design and install the full filtration system.
The fit and seal of replacement filters is just as important as the filtration media itself. Brand owners involved in private label or OEM product development should also consider those same details in the design and manufacture of filters.
HIFINE supports custom solutions for air purifier filters for brands, distributors, wholesalers, and private label customers that seek consistent filter fit, filtration performance, and production support.
