From top to bottom it is 5-1/8 long. There is a sliding door on the 16 side for filter access. The door can slide from ether side allowing for easy access. Filter for this plenum is 25 x 16 x 1.Although it normally takes a little more time and effort on our part, our products are typically rivited together. Riveting, versus spot welding, provides a more durable bond resulting in a longer lasting rigid part that will serve you for decades. We are a complete sheet metal shop. Please check out my other auctions.