RTU Replacement: What Property Managers Need to Understand Before the Project Starts

Replacing a rooftop unit (RTU) looks simple on paper: old unit out, new unit in. In practice, most surprises on RTU projects come from decisions that weren't made until the crane was already scheduled. Settle the items below early and the project goes a lot more smoothly.

Start With What's Actually on the Roof

Before anyone talks about new equipment, get a clear picture of the existing unit and the roof it sits on. A good contractor will do a site visit and note:

• Existing unit nameplate data: tonnage, voltage, phase, gas input, and heating type
• Roof curb condition and whether it matches the footprint of a replacement unit
• Supply and return duct connections and where they land on the curb
• Gas, electrical, and condensate connections
• Roof access, nearby obstacles, and overhead lines
• Whether the roof is under warranty, since roof work may involve your roofing contractor

If you have as-built drawings, original specs, or past service records, hand them over. It saves time and reduces guesswork in the bid.

Like-for-Like or Something Different?

The first decision is whether the new unit matches the old one or whether the space has changed. A tenant switch, an added server closet, or a change in occupancy can mean the original tonnage no longer fits. Replacing an undersized or oversized unit with the same size just repeats the problem.

If the load has changed, ask for a load calculation rather than a guess. If nothing has changed and the existing unit has performed well, a like-for-like replacement is usually the simpler path.

Curbs, Cranes, and Roof Access

This is where RTU projects most often pick up unplanned cost. Confirm these items in the proposal:

Permits and Inspections

Commercial mechanical work in the St. Louis area is permitted by the local jurisdiction, and requirements differ between the City of St. Louis, St. Louis County, St. Charles County, and Jefferson County. Confirm in writing who pulls the permit, who pays the fee, and who schedules the inspection. Building owners are sometimes surprised to learn that permit responsibility wasn't addressed in a proposal.

Plan the Schedule Around Your Tenants

An RTU swap usually means a unit offline for at least part of a day, and sometimes longer when ductwork, gas, or electrical changes are involved. Plan around the people in the building:

• Tell tenants early, including the expected shutoff window
• Ask about after-hours or weekend work if downtime would hurt a tenant's business
• Check for conditions that restrict crane or roof work, such as weather or lease terms
• Ask when equipment would need to be ordered so the schedule has a realistic start date

Equipment lead times vary by unit and by time of year, so get a firm answer from your contractor rather than assuming. Ordering sooner often gives you more scheduling control.

Make Sure the Scope Is Written Down

Two RTU bids that look similar can cover very different work. When comparing proposals, check what each one includes and excludes:

Items to confirm are included

• Removal and disposal of the existing unit, including refrigerant recovery
• New unit with model and capacity listed
• Curb adapter or new curb, if needed
• Crane or lift
• Duct, gas, electrical, and condensate reconnections
• Permit and inspection
• Startup and testing
• Warranty terms in writing

Items that are often left out

• Electrical upgrades or new disconnects
• Gas line modifications
• Roofing work around the curb
• Controls or building automation integration
• Repairs to existing ductwork found after the old unit comes off

One Honest Note on Replacing Early

Replacing a unit before it fails lets you control the timing, the budget, and the tenant impact. Waiting for a failure in July usually means rushed decisions. That said, a unit that still performs doesn't always need to go. If your contractor can show you why replacement makes sense, such as repeated repairs, major component failures, or changed loads, that's a good sign. If you only get urgency, ask for a second opinion.