Exhaust fan is up the top/left black fan, white mount - just one of the external vent grilles from Bunnings. you don't need heaps of airflow for cooling, just avoid stagnant air. Had to add the central support for the shelves, those 100AH of batteries are not light. Rack is set up internally like a hot isle/cold isle DC. the front door it open mesh, the front is all sealed off at the front rails. leaving the front rail back as the hot side, the rear door, was open mesh, it's all taped up, leaving the two exhaust fans/ducts the only way out for hot air.