Aerostar 20x20x2 MERV 13 Air Filter, 6 Count, ACTUAL SIZE (19.50 x 19.50 x 1.75), HVAC, Air Conditioning & Furnace Filter for Allergies, Dust, Pet Dander & Smoke (MPR 1500 / FPR 10), Made in USA

Best filters I have found at a reasonable price to construct a home made box fan filter referred to as a Corsi-Rosenthal filter. Easy to make, couldn’t be easier to use, works extremely well.

Better than the cheapies. My family is breathing much better after switching from the cheap, flimsy ones.

This isn't my first purchase of these filters so I've had some experience with them and am I repeat customer. These 20x20x2 filters fit perfectly in my system. By perfect I mean there is a small gap on each side but not so much that air gets past them. Even if it did it would be such a small amount that it wouldn't make a big difference. I see other reviewers freaking out cause they aren't completely snug in their units but I don't see how this matters as typically there are ledges the filters sit on so air isn't going to pass through every inch of their filter space. Plus, having that gap makes it easier for replacement so you can actually grab a hold of them. They seem to do the job they were built for. I have two units in my house (4 zones) and replace one filter every 2 months and the other ever 4 - 6 months. I would purchase these again.

I bought a 6-pack of these MERV13 20x20x2-inch filters to make a variation of the so-called "Corsi-Rosenthal" air-filtration device for my one-car garage, where I have a small woodshop. The air can be full of tiny particles that are not good to breathe in. Four filters are duct-taped into a box shape with a cardboard base and a 20-inch window-fan resting on top, pointing down into the box so the dust collects on the inside of the filters; the filters are oriented so air flows outward. The 2-inch thickness provides good air-flow. My only gripe is that they're fairly pricy and since I only needed four, for my purposes the 6-pack offers only acceptable value for money, not good value. But the home-made air-filtration device using these MERV13 filters delivers filtration performance comparable to an $800 piece of equipment, so in that sense, it's very good value for the money.

These work very well in my Corsi-Rosenthal box.

Fits in air conditioning

So I love these for making home made fan filters. The 2” thickness makes it sturdy and the 20x20 is the perfect size for box fans. The price is going up so that’s a bummer. But I take 4 of them and tape them together in a box formation and lay the box fan on top. The fan pulls air thru the filters and helps clean out the dander and dust from the house. After a couple months, It’s clearly evident how much it’s cleaning the air.

These work and fit as advertised, fast delivery.