VEVOR Electrostatic Air Filter, 20x20x1 inch Washable & Reusable Aluminum AC/HVAC Furnace Filter, MERV 8 Long Lifetime, Home or Office (Actual Size: 19.75 x 19.75 x 0.82 in)

Hello, both sides have the same design, so it doesn’t matter which one you choose. You can install it on either side. If this answer does not resolve your issue, please contact us again for assistance.