A ducted shelf for an open-fronted display unit employing air curtains comprises a duct extending forwardly or rearwardly through the shelf and communicating at a forward end with a discharge or return opening, the duct being wider in the widthwise direction at the forward end than at a rearward end of the duct. Guide walls divide the duct into a group of channels disposed successively side-by-side in the widthwise direction. Each channel has a respective length reflecting a degree of widthwise offset between the rearward end and the forward end of that channel. A longer channel of the group has a greater width in the widthwise direction at its rearward and forward ends than a shorter channel of the group.