Newer Carrier systems use slightly larger than standard size filters normally available in hardware stores. Therefore, I had installed a replacement exterior duct cover that is easier to replace the filter than the system on my Carrier under unit filter. This allows me to use an 18 x 24 filter which is 8 sq in larger than the filter it replaces. And it is very easy to replace, unlike the Carrier system. This also provides a larger surface area which allows less restriction of the N-95 filter, which shouldn't be an issue if you change filters regularly. If a filter is heavily coated with debris, it is well overdue for changing. These filters are effective in removing allergens, as my symptoms have reduced after a week or so after installation.

20x20 Filters received promptly and in good condition. Fit is slightly smaller than opening but still good. In use now for two weeks and is doing a good job. Cannot confirm filtration specs but fully confident with American made product by Armbrust.

Thank you for selling in cases so that the cost is comparable/better than the lower MERV 3M filters that I typically use. My biggest concern was whether my AC can handle the resistance of this filter. I confirmed with my AC company that it can take MERV13. I also did a basic airflow resistance test of this filter vs. my 3M filter--I used a hairdryer to blow a ball that is on the other side of each filter, and compared the distance the ball traveled. The airflow was comparable between the two filters. I would love for Armbrust to publish resistance data to help consumers.

I haven't had the filters long enough to know how well they work. I trust the Armbrust brand for my health masks and believe that the filters will prove to be as reliable. I truly appreciate the opportunity to try these filters at a reduced price with free shipping. I highly recommend this company and their products!

I like them despite the frame being slightly smaller than what I had been purchased from L****.