How To Make A DIY Air Purifier (5 Easy Steps!)

Having great indoor air quality is important for both your health and your comfort. Since the average person spends a fair amount of time at home, a good filtration system is a high priority.

Considering good air quality should be accessible to all, we have come up with 5 easy steps on how to make your very own DIY air purifier. Keep reading below to find out more!

How To Make A Homemade Air Purifier

If you’re on a budget or looking at a customizable homemade air filter, then the steps below will be easy to follow.

Our tools and materials list is short, consisting of – a box fan, string or bungee cord, an air filter, pliers, and measuring tape.

Sound too good to be true? Well, studies have shown that DIY air purifiers dramatically decrease the amount of black carbon and smoke pollution in the air.

In fact, these homemade “filter fans” can remove up to 90% of small particles.[1] Without any further delay, let’s get started!

BlueAir Air Purifier Placement

Buy Any Box Fan

Order a box fan online or buy it at your nearest shopping center. Box fan sizes may vary, but we recommend a unit that will measure around 20 x 20 inches in length and width.

If you’re unsure of the size, use your measuring tape in-store!

Additionally, you should see to it that your box fan has a flat front and back, as this will allow you to easily strap your filter on later.

Box fans with a flat front will have a recessed motor, so be on the lookout for that feature.

Buy a Filter That Is Similar Size

Before buying a filter for your DIY air purifier, there are two guidelines you should follow. The filter must be the same size or larger than your fan, and it should specify what it can filter.

For our guide, we have chosen a HEPA filter (more on that later), but you may opt for a MERV filter if you’d like.

Whatever you decide to go with, just make sure it overlaps your box fan, and can effectively protect your home against wildfire smoke, harmful particles, and allergens.

Remove The Grating From The Fan (Where Possible)

Depending on where your fan controls are, you may need to remove the grating from the front of the fan. This will also increase the amount of airflow leading into the filter.

The fan knob, in particular, can get in the way of a HEPA filter. Therefore, use your pliers to pull off the knob and grating, so you have a perfectly flat front surface.

We should caution that this step may void the warranty of your fan. You’ll also no longer be able to control the speed of your fan since the knob has been removed. For that reason, set your fan speed to the max before pulling off the knob.

This step isn’t compulsory, but it will provide the best mounting experience for your DIY air filter.

Attach The New HEPA Filter

Grab your string or bungee cord, and attach the HEPA filter to the front of your box fan. You could probably use tape or rope, but high-quality string fastened in a tight knot is optimal.

There are various sources online that state you should attach your air filter to the back of your fan. While this isn’t necessarily wrong, studies and data have shown better results with a front-facing filter.[2]

Enjoy Cleaner Home Air

You can now enjoy your new DIY air filter. Remember to place it in the room that you are in the most!

MERV Filters Vs HEPA Filters: Which Is Best To Use?

MERV, also known as “Minimum Efficiency Reporting Value” is a system used to analyze the effectiveness of an air filter.

The higher the MERV rating, the higher the air filtration capabilities. MERV ratings range from 1 to 20 and can withstand particles of 0.3 microns upwards.

Filters with MERV ratings of 17-20 are usually found in nuclear power plants and can remove more than 85% of airborne particles.

On the other hand, filters with a MERV rating of 12 to 16 can be used in residential homes and can remove up to 75% of airborne particles.[3]

HEPA or High-Efficiency Particulate Air filters are designed to capture all viruses and contaminants immediately. HEPA filters do not have a MERV rating because they are guaranteed to perform better.

All HEPA filters must therefore meet a minimum efficiency of 99.97%, consequently making them ideal for places such as hospitals.

A DIY HEPA filter may have higher efficiency, but they are often more expensive when compared to MERV filters. Be that as it may, consider the current quality of your air.

If your home is prone to pollution, or you want to filter smoke, then it may be time to spend a little more.

HEPA Filter for Air Purifier

How Effective Is Your DIY Air Purifier Against Common Problems


Common airborne allergens include pollen, spores, and pet dander. As long as the particles are above 0.3 microns in size and the MERV rating is above 16, you should be able to filter out 95% of allergens.

The HEPA filter improves upon this with 99.97%.


Dust will likely be larger than 0.3 microns in size, so your DIY air purifier will stand an even greater chance of trapping particles.

A MERV rating of 12 and above can trap up to 90% of particles that are 3 to 10 microns in size.

Viruses / Covid

There’s no solid research to back up how effective your air purifier will be against COVID-19.

However, at 0.1 microns, the COVID-19 molecule theoretically is large enough to be caught by a HEPA filter. As to what actual percentage that relates to, we do not know.

Pet Hairs and Odors

Since pet hairs can have a density of more than 50 microns, your air filter should catch a lot of floating strands.

In contrast to that, tiny particles, such as the odors released from sulfur at just 0.0004 microns will get through most air filters and purifiers.

What Is A Corsi-Rosenthal Box?

A Corsi-Rosenthal box is a DIY air purifier that was designed during the COVID-19 pandemic to reduce the levels of viral particles indoors.

Unlike a traditional box fan filter design, the Corsi-Rosenthal was originally made to house 5 filters (preferably MERV 13 and higher) on the sides and bottom of the cube.

A 20-inch fan would then be mounted with duct tape on the top of the cube to draw air through the filters and up/out of the box. The overall cost fluctuates from around $50 to $150.

Important Tips While Using A Fan

  • The filter fan should be positioned in the middle of the room, away from walls and drapes.
  • If your house is particularly large, you may need multiple air purifiers/filters.
  • MERV filters should have a rating above 12
  • HEPA filters should be replaced every 6 months.
  • MERV filters should be replaced every 90 days.
  • Close all windows/doors for the best results.

Frequently Asked DIY Air Purifier Questions

How much does it cost to make your own DIY air purifier?

A DIY air purifier should cost a fraction of an air purifier sold online at sites like Amazon. The total cost should be approximately $25 to $50.

The price will fall between these ranges based on the type of filter and the quality of the fan.

How long does it take to make you a DIY air purifier?

You can complete the entire DIY air purifier project in just 5 minutes! If you’re still unsure, search YouTube, and you’ll find multiple videos to watch that go through all the details/steps.

Are there any risks when making your DIY air filter?

The only thing to look out for is the age of your fan. Make sure it is newer than 2012 to avoid any potential fire hazards.


In summary, it’s quite simple to make your own air purifier box fan in 5 easy steps. With a 20×20″ box fan, a high-quality filter, string, and a few workshop tools, you’ll be making a DIY air filter work for you!



Last Updated on February 13, 2023

Josh M