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How to Make a DIY Air Filter

Ross Trethewey explains how air filtration systems work and how to build a localized DIY air filter.

Home technology expert Ross Trethewey shows how air filtration systems work and how to build a localized DIY air filter.

What is a MERV Air Filtration System?

MERV stands for Minimal Efficiency Reporting Value, a value that measures how effectively a filter stops particulates of varying sizes from passing through and into the air system.

The higher the rating, the more effective the filter is at capturing smaller particles. Ratings 1-16 are HVAC use; in general, houses usually have around a MERV 5-12 system. MERV 17-20 are HEPA filters that are used in hospitals and laboratories.

Can I Install a MERV 16 or HEPA Filter Myself?

Homeowners cannot just install a MERV 16 or HEPA filter into their homes. In many circumstances, the HVAC systems homeowners have in place simply aren’t strong enough to handle higher-rated filters, as the more filtration the air has to go through, the more resistance it has to overcome.

Even if you were to get a thicker filter that increases surface area, meaning less resistance, you’ll have to check if your HVAC system has enough space to install a thicker filter. Check with an HVAC technician to check what rating your system can handle.

Steps for Building a DIY Air Filter:

If you are unable to acquire a higher rated filter, Ross demonstrates how to build your own DIY air filter. By taking four MERV-13 air filters and duct taping them on all four sides of a box fan, you’ll have a localized air filter for any room you want.

For about $150, you can have some peace of mind during wildfires and other disasters that impact our air quality.

  1. Cut out a piece of cardboard that’s the same size as the box fan to use for the back.
  2. Place the cardboard on a table and take the four air filters and stack them on the edges of the cutout, with the airflow arrow pointing in (air intake side).
  3. Take duct tape and secure each filter to the fan.
  4. Duct tape the cardboard backing.
  5. Place the fan on the other side and secure it with duct tape.
  6. Remember that you’ll have to replace the filters every once in a while. For Ross’s DIY system, the filters should be replaced about every six months.


Ross built the air filter using four, 20x20x2, MERV-13 air filters, which Ross got from Filterbuy. He duct-taped the filters to a cardboard box and a 20-in 3-Speed Box Fan, which is manufactured by Lasko, though any 20” fan would work for this application.

Expert assistance with this segment was provided by Neil Comparetto.