Undersized/possibly mislabeled FilterBuy HVAC filters.
I found that FilterBuy 20 x 25 x 4 filters are actually significantly smaller than advertised and are too small for many HVAC units. So be careful looking for a bargain. When you select 20 x 25 x 4 on their web site you get the smaller filters. In small print on the page, you'll see the actual size. FilterBuy must have rounded up from 19.375 to 20 inches, 24.375 to 25 inches, and 3 5/8 to 4 inches. It's deceptive. Since the filters are too small for many HVAC systems, they let dirt flow around them into the unit and the air in your home. It doesn't matter what the MERV level you buy since the filter allows air to flow around it. FYI, When I contacted the FilterBuy, their rep said I exceeded the 90-day refund window. When I explained that the filter was undersized, they told me it said the right size on the web site (in small print under actual size). Yep even when you click 20x25x4, you are taken to the undersized filter. When I asked to escalate, they said, “No exceptions.” My HVAC guy said the FilterBuy filter does not fit my HVAC unit and may invalidate the warranty. I'd avoid FilterBuy.