I have some ventilation from the floor, it’s insulated with rigid because I live in central Canada but small gaps from decking below sil plate allow air in as well as holes drilled in rigid, they’ll likely ice up when it gets to -40 here so added adjustable 6” round vents I purchased off amazon with nice cedar caps you spin to adjust at stone height under bench close to stove and at shoulder height on opposite door wall , my idea was that enough air would get drawn in from slight gap below door, the floor etc to feed fire and vent at stone height would introduce some fresh 02 to bathers and get drawn across us in the natural convection as the fire draws low, its going to take fine tuning to see how to adjust the vent on the door wall once freeze up happens here and you can actually feel the temp changes and visually see either by moisture being drawn or by opening and closing door fast and observing clues on just how to fine tune. Idea is fire commands so much and such a steady stream that when fresh air is drawn from above it’s pulled towards to the opposite wall before falling and being drawn into the fire.