Monoxivent's Single Wall & Double Wall UnderDuct Solutions UnderDuct is leading the way for code compliant LEED driven underground HVAC systems. UnderDuct is a corrosion resistant, high strength, light weight, Class 1 duct material, per NFPA 90. UnderDuct is ideal for displacement ventilation, allowing for the most economical long term energy savings. UnderDuct is shop fabricated with a minimum number of field joints. Monoxivent has a nationwide network of sales representatives and a top-tier inside support staff that provides engineering, design, sales, service, and marketing. UnderDuct is offered both in single wall and pre-insulated double wall construction to meet any ventilation needs. UnderDuct can be used in above ground applications, not just underground. UnderDuct also comes in a variety of configurations to fit your project needs.