A rooftop unit replacement scope should state the unit by tag and capacity, how it meets the roof (existing curb, adapter or new curb), who lifts it, who reconnects power, gas and condensate, what economizer and Title 24 acceptance work applies, how the roof is protected, and which startup and warranty documents the owner receives. Gaps at the curb and at the electrical disconnect cause most change orders.
- Name the new unit by tag, model basis and capacity, and say what happens to the old one, including refrigerant recovery and haul-away.
- The curb decides the job. Settle reuse, adapter or new curb before bid day, and say who confirms the roof structure can carry the new weight.
- Electrical, gas and condensate each need a named owner. Mechanical work stops at the unit; the scope must say where.
- Economizer, fault detection and acceptance testing are part of a compliant change-out, not extras. Confirm current Title 24 requirements for the unit size.
- Closeout means startup sheet, warranty registration, permit sign-off and updated asset records, listed in the scope before the first bolt moves.
The line items a change-out scope should carry
A change-out looks simple because one box leaves and one box arrives. The cost and the surprises sit in everything around the box. Write the scope as a short list of line items, each with a result, so two bidders price the same job. The general method is in how to write a commercial HVAC scope of work; this page narrows it to rooftop units.
| Line item | The scope should say |
|---|---|
| Equipment | Tag, tonnage, heat type, voltage, coil coating, controls option, and the basis-of-design model or approved equal |
| Removal | Disconnect, refrigerant recovery, lift-off, and where the old unit goes |
| Curb | Reuse, adapter or new curb, and who verifies dimensions and roof capacity |
| Lift | Crane size, street or lot permits, staging area, and lift window |
| Utilities | Power, gas, condensate and control wiring, with the trade responsible for each |
| Controls and economizer | Thermostat or BAS connection, economizer, fault detection, and acceptance testing |
| Startup | Commissioning readings, safeties tested, airflow verified |
| Closeout | Warranty registration, permit final, as-built tag data |
Curb, structure and the crane lift
Equipment generations rarely share a footprint. A new unit may have a different curb opening, a different supply and return location, or a different weight. The scope should require a field measurement of the existing curb before equipment is released for fabrication, and should state what happens when the measurement does not match: an adapter, a new curb, or a ductwork transition.
- Reuse: only after the curb is inspected for rot, rust, flashing condition and level. A curb that has leaked for years is not a candidate.
- Adapter: a fabricated transition between the old opening and the new unit. Say who builds it, who flashes it, and who warrants the roof penetration.
- New curb: brings roofing and structural work. Name the roofer and the engineer; Davinci's own crew handles mechanical, refrigeration and controls, so those trades must be named by the owner or GC.
The crane is rented equipment that Davinci coordinates; it is not a separate trade. Even so, the scope needs the details that make a lift legal and uneventful: boom reach, truck placement, parking-lot closure or sidewalk permit, drive aisle protection, and a set time so tenants can be warned. Weight and rigging points are covered further in equipment removal, crane and rigging scope of work.
Disconnects, gas and condensate at the unit
Treat the unit connection as three small projects with three owners.
Electrical
A bigger or more efficient unit can carry different amperage, breaker and wire requirements. Primary electrical service, feeder and panel work is not part of Davinci's self-performed mechanical, refrigeration and controls scope, so the scope must name the licensed electrical contractor responsible for any feeder, breaker or disconnect change. The owner or GC should confirm that party in writing. Mechanical work covers unit-side connections and control wiring that belong to the controls scope.
Gas
For gas heat, state the meter and line capacity assumption, the drip leg, shutoff and union arrangement, vent termination, and who pressure-tests the connection. If the roof gas line is corroded or undersized, say whether replacement is included or an alternate.
Condensate
Specify the trap, the slope, the overflow switch and where the line ends. Draining onto a roof membrane or into a stairwell is not a scope, it is a future complaint. Pairing the drain with a float switch that cuts the compressor is cheap protection for ceilings below.
Economizer, fault detection and Title 24 acceptance
California's energy code generally treats a like-for-like replacement of a packaged unit as an alteration, and the new unit is expected to meet current Part 6 requirements for its size and climate zone. That commonly brings an economizer, controls requirements and acceptance testing by a certified technician with forms filed against the permit. Requirements change between code cycles and depend on capacity, so the scope should say confirm current requirements with the building department and state the assumption used in the bid.
Write the economizer into the scope as a tested function: damper travel verified, changeover sensor calibrated, minimum outside air set to the design value, and fault detection reporting working. For the permit side, see Title 24, permits and HVAC replacement and the commercial RTU replacement overview.
Contractor shall remove the existing rooftop unit tagged RTU-3, recover refrigerant per EPA requirements, and set a new unit of equal or greater capacity on the existing curb after Contractor verifies curb dimensions and condition. If the curb is found unsuitable, Contractor shall notify Owner before proceeding and price a curb adapter or new curb as a separate item. Contractor shall perform startup, economizer functional testing and any acceptance testing required by the permit.
Roof protection, sequence and downtime
Roofs are warranty documents. Many roofing warranties are voided by unprotected traffic or by an unapproved penetration, so the scope should require walk pads or plywood along the path, drip protection under refrigerant and oil work, and a final inspection with the owner's roofer where a warranty exists.
- Submittals approved and equipment confirmed on site or on a firm delivery date.
- Tenant notice issued and the lift window confirmed with property management.
- Unit isolated, refrigerant recovered, gas capped, power locked out.
- Old unit lifted off; curb cleaned and inspected.
- New unit set, sealed to the curb, and connected.
- Leak check, startup and economizer testing.
- Cleanup, roof walk with owner, closeout documents.
Occupied buildings need a temporary cooling plan for server rooms, labs, kitchens and anywhere heat load cannot wait a day. Say who supplies it.
What is commonly missed
- Old curb flashing and counterflashing, which is not mechanical work but is exposed the moment the unit leaves.
- Return and supply duct transitions when the new unit's openings are offset from the old.
- Smoke detector in the return or supply duct, where the code or the unit requires one.
- Vibration isolation and seismic restraint for the unit, depending on building and jurisdiction.
- Condensate line extension, trap height and freeze or overflow protection.
- Thermostat or BAS point mapping, so the unit reports to the system after the swap.
- Disposal documentation for refrigerant, oil and the old unit.
- Overtime or night work when the lift must happen outside business hours.
Clarifying these in writing is faster than arguing about them later. A short clarifications and exclusions checklist helps, and the common triggers for added cost are covered in HVAC change orders: what triggers them.
Submittals and closeout
Submittals go in before equipment is ordered: product data with the options actually selected, rigging or lift plan, curb or adapter drawing, and electrical data for whoever sizes the feeder. Closeout is the same discipline in reverse.
- Startup and commissioning sheet with readings, signed by the technician.
- Warranty registration confirmation with the manufacturer, in the owner's name.
- Permit final and any Title 24 acceptance forms.
- Nameplate data, filter sizes and belt sizes for the maintenance file.
- Photos of the set unit, curb connection and disconnect.
On Davinci projects the new unit is added to the DaVinci Portal with a QR-coded record, so service history, readings and photos start on day one rather than after the first failure.