The project involved replacing three existing Trane rooftop units mounted on structural dunnage and connected to main supply and return air trunk lines. The units had reached the end of their service life, and building ownership needed a modern, efficient replacement that minimized installation complexity while maintaining system performance and compatibility with the existing ductwork.

Replacements like this are rarely as simple as swapping like for like. Existing structural steel, duct connections, and an occupied building all constrain the design, and every field modification adds cost, schedule risk, and disruption for the tenants inside. Crane time, roof work, and system downtime all had to be kept to a minimum, so the replacement strategy had to work with the building’s infrastructure rather than against it. At 105 tons per unit, this was not an off-the-shelf swap; equipment at this scale has to be engineered to the installation, and selection be

The solution used AAON E-Series Cabinet Rooftop Units paired with solid bottom plenum curbs. The curbs were positioned on the existing steel dunnage, aligning the new units’ supply and return openings with the current duct systems. This eliminated the need for extensive duct modifications, shortened the construction schedule, and reduced installation cost, all while upgrading the building to modern, high-efficiency equipment rated at 105 tons per unit. The solid bottom plenum curbs do double duty in a replacement like this: they provide a weather-tight structural transition between the unit and the dunnage, and the plenum routes supply and return air to the existing duct openings without field-fabricated transitions.

AAON’s configurable cabinet construction gave the team the flexibility to match the existing openings precisely, and H.C. Nye’s application support confirmed the fit before anything was lifted to the roof. Each unit was checked against the existing dunnage geometry and duct connections during selection, so installation day held no surprises. The E-Series platform also delivered what the owner wanted long term: high-efficiency operation, durable double-wall cabinet construction, and capacity matched to the original design without oversizing.

For building owners facing end-of-life rooftop equipment, the project is a proven approach: reuse what the structure already provides and let the new equipment adapt to the building rather than the other way around. It is also a repeatable one: many commercial buildings of this era carry rooftop equipment on structural dunnage, and the same curb strategy applies wherever the existing steel and ductwork remain sound.