This insulated 16x25 return plenum (B Cabinet) is designed to house either a 1" or 4" filter, offering flexibility for standard or high-efficiency filtration. Built with durable, galvanized steel and fully lined with insulation, it helps reduce noise and condensation while improving airflow. Compatible with most residential HVAC systems requiring a 16x25 return size, this plenum ensures cleaner, quieter, and more efficient operation.