Fresh-air exchange is more important than simply recirculating the same air. In a darkroom, trays and chemicals can release vapors, and a fan that only stirs the room air may increase evaporation without removing those fumes.

A better approach is to exhaust air from the room with a light-tight vent or extractor fan. Replacement air can usually enter through small gaps such as around the door, as long as the room is light-sealed rather than fully air-sealed. To prevent light leaks, use a baffle or “light labyrinth” instead of relying only on curtains. A matte-black, curved or boxed vent path can block light while still allowing airflow.

If you do add intake or circulation, dust control is also worth considering, since moving air can carry lint onto prints and equipment. In short: prioritize ventilation with fresh air exchange, keep it light-tight with baffling, and avoid relying only on internal circulation.