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Make Your Own Room Air Purifier

One of my children went back to graduate school recently with a cheapo air purifier I’d made out of a $16 furnace filter and a $20 box fan. In the midst of a pandemic spread mostly by airborne virus particles, I wanted my child to breathe clean air.

My child has a small HEPA air purifier for the bedroom. But the DIY air purifier I made was meant for the apartment’s shared living area. I also wanted my child to be able to pay for the replacement filters on a graduate-student budget. That wouldn’t have been possible had I bought a $600 air purifier.

You need three ingredients to make this DIY air purifier: a box fan, a 20″ by 20″ by 1″ high-quality furnace filter, and packing tape. Two videos I watched — one from a University of Minnesota doctor and another from The New York Times — suggested taping the furnace filter to the front of the fan. I rejected that idea, and taped the filter to the back of the fan.

I can’t see that it makes any difference whatsoever which end of the fan the furnace filter is attached to, except for #1 aesthetics and #2 the fan stays cleaner if the air is pulled through the filter before it hits the fan. Either way, air is moving through the filter, which is electrostatically charged so the particles in the air stick to the filter, and you don’t have to breathe them in.

I don’t think there’s any reason to hermetically seal the furnace filter to the fan. This cheap DIY device is filtering the air in an enclosed room. If some of the air escapes around the edges of the filter well, it will get caught in the filter the next time the fan grabs it. At least that’s the plan.

The $20 box fan I bought has a metal frame, which makes it fairly sturdy. I bought a black one because my child requested it. In my attic, I have a 10-year-old version of the same fan, which is still going strong.

A HEPA air filter, the most effective filter for cleaning icky stuff out of the air, is rated MERV 17 or higher. I purchased MERV 13 rated furnace filters for this DIY air purifier, but higher rated furnace filters are available.

According to The New York Times, this type of DIY air purifier with a MERV 13 furnace filter removed 87% of smoke particles in the air, compared with 99% of smoke particles removed by an air purifier with a HEPA filter. I chose the MERV 13 filters because they were on sale. Price does matter, since these filters have to be replaced every three months.

This DIY air purifier is certainly better than no air purifier, although a device with a true HEPA filter would work better. During this pandemic, it makes sense to filter out as much of the dust, bacteria, mold, and viruses that float around inside our homes as possible. For this price, you can make DIY air purifiers for nearly every room in your house and spend less than you would on a single HEPA air purifier.

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To make a DIY air purifier, all you need are a 20″ square box fan, a 20″ by 20″ by 1″ MERV 13 furnace filter and some packing tape.

A filter rated MERV 13 removes many allergens, bacteria and virus particles from room air.

The MERV rating is printed on the filter.

An arrow on the box indicates the direction of the air flow. I put the filter on the back of the fan, but it can be attached to the front, as long as the arrow points in the direction of the air flow.

Place the fan on a flat surface, face down.

Use packing tape to attach the filter to the back of the box fan. I use two pieces of tape per side of the fan. Make sure the arrow points toward the front of the fan, as that’s the direction air flows through the fan.

That’s it! The air purifier is ready. The fan won’t create much of a breeze since it has to work hard to pull air through the filter. I keep mine on low speed to avoid overheating the fan motor.

Place the air purifier in a convenient spot, plug it in, and let it filter the air.

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