Monessen Outside Air Kit AK22Monessen Outside Air Kit AK22 Product Details An optional outside air kit is designed to introduce fresh, outside air to the firebox as desired. It is an important accessory in newer, more air tight construction for an adequate supply of fresh air. Although it is not a requirement for a vent free firebox, some local building codes may require the addition of an outside air kit. Features: Prevents Negative Pressure Enhances Efficiency Reduces Heat Loss