An automated grid based storage and retrieval system includes a framework structure and a plurality of storage containers. The framework structure includes upright members and a grid of horizontal rails provided at upper ends of the upright members. The framework structure defines a storage volume including a plurality of columns arranged in a grid pattern below the horizontal rails between the upright members. The plurality of storage containers are stacked vertically in stacks in the columns to provide a plurality of storage columns. An under-stack void extends beneath the stacks of storage containers. A plurality of inlets lead to the under-stack void between the stacks of storage containers. At least one column, which is empty of storage containers and arranged amongst the storage columns, provides a ventilation column. The ventilation column includes a fan. A plurality of duct walls surrounding the ventilation column define a duct having a first end adjacent the horizontal rails and a second end adjacent the under-stack void. The fan is arranged to circulate gas along sides of the stacks, via the plurality of inlets and the under-stack void, and through the duct.