A storage system comprising: a plurality of upright members; two substantially perpendicular sets of rails (22a, 22b) supported by the plurality of upright members and forming a grid above a workspace, the workspace comprising a plurality of stacked containers, each stack of containers in the workspace corresponding to an opening in the grid; and, a plurality of robotic load handling devices operating on the grid above the workspace, the load handling devices comprising a body mounted on wheels (34, 36), a first set of wheels being arranged to engage with at least two rails of the first set of rails, the second set of wheels being arranged to engage with at least two rails of the second set of rails, the first or second set of wheels (34, 36) being independently moveable and driveable with respect to the other of the first or second set of wheels (34, 36) such that when in motion only one set of wheels (34, 36) is engaged with the grid at any one time thereby enabling movement of the load handling device along the rails to any point on the grid by driving only the set of wheels (34, 36) engaged with the rails (22a, 22b), the load handling devices being provided with means for lifting out one or more containers from a stack through a corresponding opening in the grid, characterised in that the storage system further comprises: at least one heater and/or at least one chiller located above the workspace for generating a reservoir of temperature controlled gas above the workspace; a plenum comprising an opening adjacent a side of the stacked containers for receiving the temperature controlled gas; at least one fan being adapted to circulate temperature controlled gas through the stacked containers to the plenum; and, a plurality of ducts formed as tubes provided in the upright members and extending between them, the tubes being configured to further aid the circulation of temperature controlled gas from the reservoir to reduce temperature variation throughout the stacks of containers, wherein each storage container comprises one or more apertures in the sides to allow the temperature controlled gas to circulate freely through the storage container. a plurality of upright members; two substantially perpendicular sets of rails (22a, 22b) supported by the plurality of upright members and forming a grid above a workspace, the workspace comprising a plurality of stacked containers, each stack of containers in the workspace corresponding to an opening in the grid; and, a plurality of robotic load handling devices operating on the grid above the workspace, the load handling devices comprising a body mounted on wheels (34, 36), a first set of wheels being arranged to engage with at least two rails of the first set of rails, the second set of wheels being arranged to engage with at least two rails of the second set of rails, the first or second set of wheels (34, 36) being independently moveable and driveable with respect to the other of the first or second set of wheels (34, 36) such that when in motion only one set of wheels (34, 36) is engaged with the grid at any one time thereby enabling movement of the load handling device along the rails to any point on the grid by driving only the set of wheels (34, 36) engaged with the rails (22a, 22b), the load handling devices being provided with means for lifting out one or more containers from a stack through a corresponding opening in the grid, characterised in that the storage system further comprises: at least one heater and/or at least one chiller located above the workspace for generating a reservoir of temperature controlled gas above the workspace; a plenum comprising an opening adjacent a side of the stacked containers for receiving the temperature controlled gas; at least one fan being adapted to circulate temperature controlled gas through the stacked containers to the plenum; and, a plurality of ducts formed as tubes provided in the upright members and extending between them, the tubes being configured to further aid the circulation of temperature controlled gas from the reservoir to reduce temperature variation throughout the stacks of containers, wherein each storage container comprises one or more apertures in the sides to allow the temperature controlled gas to circulate freely through the storage container. at least one heater and/or at least one chiller located above the workspace for generating a reservoir of temperature controlled gas above the workspace; a plenum comprising an opening adjacent a side of the stacked containers for receiving the temperature controlled gas; at least one fan being adapted to circulate temperature controlled gas through the stacked containers to the plenum; and, a plurality of ducts formed as tubes provided in the upright members and extending between them, the tubes being configured to further aid the circulation of temperature controlled gas from the reservoir to reduce temperature variation throughout the stacks of containers, wherein each storage container comprises one or more apertures in the sides to allow the temperature controlled gas to circulate freely through the storage container.