Model G is a single wall negative, neutral, or positive pressure capable, stainless steel pre-fabricated piping system for use in many applications including: grease ducts, fume venting, chimney liner, chutes, particle conveying, etc. Model G is UL Listed for grease duct applications (see our ads). Model G is c-UL Listed as a chimney liner (for existing chimneys) via ULC-S635.