The 4" Outside Air Adapter is a purpose-built accessory designed specifically for the True North TN25c wood burning stove, helping ensure optimal combustion performance while improving overall home comfort. By allowing the stove to draw combustion air directly from outside the home, this adapter reduces negative pressure issues and helps maintain balanced indoor air quality — especially important in newer, tightly sealed homes. The 4" outside air adapter is required when installing the True North TN25 Wood Stove in a mobile home.  (Does not include 4" pie and outside air hood.)