Spawn run wants warm, still, wet and stale air. ICAR-DMR recirculates all of the air with no fresh-air entry, keeps carbon dioxide between 10000 and 15000 ppm, and works at 95 percent relative humidity in a controlled room. Its seasonal folder gives 22 to 25 °C and 80 to 90 percent humidity, because a naturally ventilated room cannot hold 95 percent.
Carbon dioxide is useful here. It helps the mycelium move through the compost. After casing the same gas becomes the thing you must remove, so the fan settings for the two stages are opposite.