A shrink tunnel (100) for use with packaging machines utilizing heat shrinkable film (17). Air plenums (158, 160, 162, 164) positioned in the shrink tunnel (100) accurately direct heat at laterally opposed ends (188, 190, 198, 200, 202, 204, 206, 208, 212, 214, 218, 220) of film wrapped packages (192, 194, 196, 210, 216, 222) to shrink film into a bullseye (19). The air plenums (158, 160, 162, 164) are adjustable to accommodate different size packages or a differing number of lanes of operation. Interior air plenums (160, 162) are inserted between packages in lanes of a multiple lane packaging machine so that the laterally opposed ends of all packages have hot air directed at them.