Commercial Rooftop Unit Replacement: A Facility Manager's Checklist

Rooftop units do a lot of quiet work. In most low-rise commercial buildings they handle heating, cooling and ventilation for the space underneath, and nobody thinks about them until one stops in the middle of a heat wave. By then the options are narrow: whatever equipment is in stock, whatever crane is available, and a tenant who wants an answer today.

Planned replacement gives you back those choices. This checklist is written for property and facility managers who want to approve an RTU replacement with no surprises on the roof.

1. Know what is on the roof

Start with an inventory. For each unit, record:

• Make, model and serial number from the nameplate
• Nominal tonnage and heating type (gas, electric or heat pump)
• Approximate age, which can often be read from the serial number
• What area of the building it serves
• Service history: compressor replacements, heat exchanger issues, recurring calls

A simple spreadsheet is enough. It turns a reactive problem into a plan, because you can see which units are oldest, which are costing the most in repairs, and which serve the most sensitive tenants.

2. Decide repair vs replace on facts

Not every old unit needs to come down. A failed fan motor or contactor on a sound unit is a repair. The decision tilts toward replacement when you see:

• A failed compressor or cracked heat exchanger on an older unit
• Refrigerant that is being phased down and is getting expensive to service
• Repeated failures in the same season
• Corroded cabinets, rails or coils that make further repairs a poor investment
• A tenant or use change that the existing unit cannot handle

Ask your contractor to put the repair cost next to the remaining useful life of the unit. That comparison is usually more helpful than either number alone.

3. Check the sizing, not just the nameplate

The fastest way to replace an RTU is to order the same tonnage. It is not always the right way. If the space below has changed, such as a new tenant, a different occupancy, added kitchen equipment or a lighting retrofit, the load has changed too.

Ask for a review of the cooling and heating load and the outdoor air requirements. Ventilation codes and the needs of the space determine how much outside air the unit must bring in, and that affects equipment selection, economizer requirements and energy use. Oversized units short-cycle, control humidity poorly and wear out faster.

4. Settle the curb question early

The curb is the frame the unit sits on, and it is one of the biggest variables in an RTU job:

• Same footprint. If the new unit matches the existing curb, the swap is simplest.
• Curb adapter. If the footprint differs, a factory or custom adapter lets the new unit sit on the old curb. This avoids cutting the roof, but adds height and cost.
• New curb. Sometimes the old curb is damaged or the openings do not line up. A new curb means roofing work, which needs to be coordinated with your roofing contractor so any roof warranty is protected.

Get the curb approach in writing in the quote, along with who is responsible for roofing and flashing.

5. Plan the lift

Most RTU replacements need a crane. The crane plan affects cost and scheduling more than people expect:

• Crane size depends on the unit weight and how far it must reach from the street or lot
• Street closures or lane permits may be required in denser areas
• Weekend or early-morning lifts are common to avoid traffic and tenants
• Weather can push the date, so build in a backup day

Replacing several units in one lift day often makes the crane cost per unit much easier to swallow. This is one of the strongest arguments for planning replacements across a portfolio instead of one failure at a time.

6. Confirm the connections

A complete quote should cover every connection the new unit needs:

• Gas piping and shutoff, if gas-fired
• Electrical disconnect and circuit sizing for the new unit
• Condensate drainage
• Ductwork transitions between the curb and the existing supply and return
• Controls and thermostats, including any building automation system integration
• Smoke detectors or fire shutdown interlocks where required

Gaps in this list are where change orders come from.

7. Schedule around the building

Tenants care about two things: being comfortable and being open. Agree on:

• The shutdown window for each unit and which spaces are affected
• Temporary heating or cooling if the shutdown runs long in extreme weather
• Notices to tenants with dates and times
• Roof access, keys, security and parking for the crane and crew

Commercial kitchens deserve extra attention. If a food tenant's makeup air unit or exhaust fan is involved, coordinate with them directly. It is also a good time to check when their kitchen exhaust and hood cleaning is due, since the crew will be on the roof anyway.

8. Permits, incentives and paperwork

Mechanical permits are typically required for RTU replacement, and the contractor should pull them. Some utilities and governments offer incentives for high-efficiency or heat pump RTUs, and these often require pre-approval before equipment is ordered.

Keep a project file with the permit, equipment submittals, startup report, warranty registration and as-built notes. Your future self, or the next facility manager, will thank you.

9. Insist on a real startup

Startup is where a lot of value is won or lost. A proper commissioning visit checks:

• Refrigerant charge and operating pressures
• Gas pressure and combustion on gas units
• Supply airflow and static pressure
• Economizer operation and outdoor air settings
• Controls, schedules and setpoints

Ask for the startup report in writing and file it with the unit.

10. Set up maintenance from day one

A new RTU still needs filters, belts, coil cleaning and seasonal startups. Setting up a maintenance schedule at installation protects the warranty and catches small problems before they become emergencies.

Frequently asked questions

Do you need a crane to replace a rooftop unit?

Most RTU replacements do. The crane size depends on the weight of the unit and how far it has to reach from the street or lot, and denser areas may need a street or lane permit. Grouping several units into one lift day usually brings the crane cost per unit down.

What is a curb adapter on a rooftop unit?

The curb is the frame the unit sits on. When a new unit's footprint does not match the existing curb, a factory or custom curb adapter lets it sit on the old one without cutting the roof. It adds some height and cost, so the quote should say whether an adapter, a new curb or a direct fit is planned.

Should a replacement RTU be the same tonnage as the old one?

Not necessarily. If the space below has changed, with a new tenant, different occupancy, added kitchen equipment or a lighting retrofit, the heating, cooling and outdoor air needs have changed too. A load review is worth doing, since an oversized unit short-cycles, handles humidity poorly and wears out faster.

Is a permit required to replace a commercial rooftop unit?

A mechanical permit is typically required, and the contractor should be the one to pull it. Keep the permit with the equipment submittals, startup report and warranty registration in a project file for the building.

Plan your next replacement

If you are responsible for a roof full of aging equipment, a short survey and a written replacement plan will save money and stress compared to replacing units one breakdown at a time. Our commercial rooftop unit replacement and service page explains how Vulcair HVAC scopes these projects, and you can browse our full list of HVAC services.

Request a quote through our form. Tell us the building address, the number of units and anything you already know from the nameplates, and we will follow up in writing with next steps.