Every cell in the 1866 block was ventilated and heated separately. Vents in the cell walls and tunnels under the floor are part of an air circulation system that kept cells cool in summer and aired in winter.

Each cell was separately linked to the roof ventilation tower. By circulating fresh air it was hoped to limit the spread of disease and keep the prisoners fit to work. This ingenious system meant that prisoners enduring the "silent system" could not communicate with their neighbours by shouting or tapping on the vents.