York® ZE/XN Series units are convertible single package rooftops with a common roof curb for the 3, 4, 5 and 6 ton sizes. Although the units are primarily designed for curb mounting on a roof, they can also be slab-mounted at ground level or set on steel beams above a finished roof. All ZE/XN Series units are self-contained and assembled on rigid full perimeter base rails allowing for overhead rigging. Every unit is completely charged, wired, piped and tested at the factory to provide a quick and easy field installation. All models (including those with an economizer) are convertible between bottom and horizontal duct connections. ZE Series units are available in the following configurations: cooling only, cooling with electric heat and cooling with one or two-stage gas heat.