Building Your Own Portable Air Filter
Last week we wrote about asthma and allergies peaking in September. In this post, we continue our focus on prevention by showing you how to make an effective in-home air filter at low cost.
Use What You’ve Got
We wrote about purposefully using the air filter in your heating/cooling system in last week’s blog post about asthma peak week. We noted your air handler may not run for long periods during shoulder seasons. You might go more than twelve hours without the air handler moving air so you’re not getting the benefit of the air filter in your heating/cooling system.
That condition can allow asthma and allergy irritants levels in your indoor air to increase over the long periods without any air filtration. What if you only want filtration and don’t need any temperature control?
Who Are Corsi and Rosenthal?
Richard Corsi, an environmental engineer and Dean of Engineering at the University of California, Davis, developed the idea of combining common air filters with a box fan to make a simple, do-it-yourself air filter. This was in response to the COVID-19 pandemic - the virus is airborne so it’s possible to mitigate the spread of the virus with improved air filtration.
Corsi contacted Jim Rosenthal, the CEO of an air filter manufacturer named Tex-Air-Filters. They had worked together in Texas to test attaching a single air filter to a box fan. Corsi’s idea called for using multiple filters rather than just one and Rosenthal developed a design that used five filters.
The five filters in Rosenthal’s design made up the bottom and four sides. The box fan was affixed to the top to blow air into the filter chamber. The result is the box fan constantly moves air through four filters for a high level of effective filtration. (Air moves through four filters because at least one is on the floor so little to no air is flowing through it.)
The filters are 20” filters and the box fan is 20” so they fit together with a bit of cardboard and duct tape. The filters are MERV-13 or higher so they can filter very small particles and viruses.
When it comes to air filters, higher efficiency is not always a good thing. Higher-efficiency filters are more challenging to push air through. That’s one of the challenges with HEPA filters - they’re typically very small and don’t move much air or they’re part of enormous and costly systems in hospitals and some manufacturing facilities.
A MERV-13 filter offers good filtration and is common in the marketplace. The old gas furnace and air conditioner in the picture above has a 4” pleated filter (in the yellow box between the silver return air duct and the green air handler) that’s rated at MERV-13. However, it only works when the fan in the air handler is running.
“Corsi-Rosenthal Box” by Festucarubra is licensed under CC BY-SA 4.0
If you’re going to build your own filter box, we recommend using four filters. The design with four filters is sometimes called a “Comparetto Cube” yet no one seems to know that… or the name “Corsi-Rosenthal Box”. Both sound like some sort of science-fiction device.
You should be able to build a four-sided DIY filter box for less than $150, including the box fan. A portable filter can cost $500 or more and you might find the company that makes the expensive filter happens to also be the only company that makes the size filter that fits in the device.
You can see the build up of filtered particles in a MERV-13 filter so you just have to look at it to gauge when it needs to be replaced. It will enjoy a longer life if you can keep it from being clogged with pet hair and other fine elements that can restrict air flow.
Where Would You Use a DIY Filter Box?
A DIY filter box might be a helpful solution for anyone suffering from allergies and asthma, especially if you’re in a home with poor filtration and air leaks. The filter box won’t help with indoor humidity levels though it can deliver up to 600 cubic feet per minute of “clean” (filtered) air. That’s better than many expensive HEPA portable air cleaners.
This could also be a solution for people who are dealing with smoke from wildfires. Georgia doesn’t often experience wildfires though fires have been commons enough that we can remember the last couple of large fires. In one event, metro Atlanta was covered in smoke blown in from fires in North Carolina.
That smoke combined with high levels of ozone in the summer can be a combination of powerful irritants for people with asthma. Having a DIY filter box or the parts you can assemble quickly might let you respond to whatever level of irritants begin to cause health problems. It can also be a fun project for children.
Leave a comment below to let us know if you’ve built a filter box or would consider building one. What would be the hardest part? Do you have any concerns about using a filter box?
Thanks for sharing and being in touch with us!
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