Yeah, the goal is a linear drop from 25°C at the top of the shelf to 22°C near the bottom, keeping the variance under 1.5°C across the stack. I’m using 12 V PWM fans set to 35 % duty, a 120 mm radiator for the heat sink, and a 0.1 µF ceramic at the fan supply for ripple suppression. That gives a 60 dB noise floor, so the only thing that’ll disturb you is a book falling off. What’s the layout you’re working with?

Sure thing. Picture a 120 mm fan mounted directly under each shelf, spaced 30 cm apart. The fan’s front air outlet faces the shelf surface, pulling the cooler air up from the bookshelf. Between the fan and the first shelf I keep a 0.5 mm spacer made from polycarbonate, just to prevent any back‑flow. The radiator sits beneath the fan array, attached to the same 12 V supply, and is a 200 mm by 80 mm copper plate with a 1 mm thermal pad on top. The fans run at 35 % PWM, which gives about 120 CFM per fan; that’s enough to push the stack’s heat out while staying below 60 dB. If you keep the shelves at 30 cm, the airflow will be steady enough that the temperature difference between the top and bottom shelves stays under 1.5 °C. That’s the layout in a nutshell.