Rooftop Installation Day: What Actually Happens When You Swap a 10 Ton Unit (Tony’s Full Walkthrough)
Most commercial building owners think rooftop HVAC replacement is simple:
Old unit comes off. New unit goes on. Done.
If only.
Anyone who’s lived through a commercial RTU replacement knows the truth: installation day is a coordinated dance between crane operators, HVAC techs, electricians, roofers, inspectors, building managers, and sometimes the fire department, traffic control, and half your tenants.
Replacing a 10-ton rooftop unit is one of the most complex maintenance events you’ll ever schedule for your building. It affects comfort, safety, operations, and even your business hours. And if you don’t know what’s coming? Installation day can hit you like a freight train.
So let me walk you through the real process—step by step—with the kind of detail only someone who’s been on too many rooftops can give you.
If you want the full Tony version of rooftop unit replacement, buckle in. This guide will tell you exactly what happens, why it matters, and how you avoid the kind of mistakes that cost thousands.
Before Installation Day: The Prep Nobody Sees
Long before the crane ever shows up, good contractors do their homework. This is the part most people never see but critical for a smooth install.
Measurements, Models, and Compatibility
Contractors verify:
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Existing curb dimensions
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Supply and return duct location
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Electrical service size
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Gas line routing (if applicable)
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Building access
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Roof loading
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Unit weight
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Ladder and hatch access
This first step alone can save you thousands by avoiding curveballs on installation day.
Pictures, Pictures, Pictures
No contractor wants to discover surprises on crane day. They review:
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Roof layout
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Unit location
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Parapet walls
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Obstructions
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Distance from drop-off point
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Distance from crane placement
[Commercial Roof Access Considerations]
If a contractor doesn’t ask for photos?
That’s a red flag.
Curb Adapter Decision
If your new unit doesn’t match the old curb footprint, a custom curb adapter is made in advance. This is one of the biggest factors in installation complexity.
Mechanical, Gas, and Electrical Disconnect Prep
Building power may need to be shut off.
Gas supply may need to be isolated.
Roof access must be cleared.
Scheduling Crane Access & Permits
Crane scheduling is an entire operation:
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City permit for crane placement
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Police detail (in some cities)
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Street closure permission
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Flaggers or traffic assistants
Here’s a general crane-permit planning reference:
[Crane Placement and Permitting Guide]
Crane companies are booked weeks out in summer.
Good scheduling prevents chaos.
Installation Day: The Real Work Begins
When installation day hits, the crew arrives early—usually at sunrise—to beat wind, traffic, and heat.
Let’s break down exactly what happens.
Step 1: Safety, Setup, and Rooftop Access
The day starts with:
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Crew safety briefing
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Ladder or roof hatch securing
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Harness checks
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Rooftop hazard inspection
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Crane coordination
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Walkie communication checks
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Electrical and gas line shutoff
If the building is open for business, tenants are notified and staff redirected as needed.
Safety slows things down, but trust me—it prevents accidents.
Step 2: Disconnecting the Old RTU
The old rooftop unit must be completely disconnected before the crane can touch it.
This includes:
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Lockout/tagout of electrical circuits
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Removing conduit and wiring
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Disconnecting low-voltage controls
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Disconnecting gas piping
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Detaching drain lines
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Removing vibration pads
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Scraping old sealant
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Removing mounting bolts
Most older units have been sitting in place for a decade or more. The fasteners are corroded, the sealant is hardened, and the metal is warped. Techs usually need:
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Impact drivers
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Penetrating oil
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Pry bars
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Tin snips
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Metal cutters
Nothing about this step is quick.
Step 3: Crane Lift – Removing the Old Unit
The crane operator communicates via hand signals or radio with the rooftop crew.
Slings are attached to the old unit at designated lifting points.
Here’s a general conceptual reference on lifting rigging considerations (placeholder):
[HVAC Rigging and Lift Points Guide]
Then:
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The crane slowly tensions the cables
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The unit separates from any remaining roof adhesion
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It lifts vertically
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It is swung away from the building
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It is lowered to a safe drop zone
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It’s strapped for transport
This step requires precision. One bad wind gust or miscommunication and things can go wrong fast.
Step 4: Preparing the Roof & Curb
Once the old unit is off, the curb is exposed for the first time in years.
The installation crew:
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Removes old sealant
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Removes debris
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Inspects curb insulation
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Checks wood and metal integrity
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Seals any gaps
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Ensures the curb is level
If a curb adapter is being used, it is installed now.
This step determines whether your new unit sits properly.
A poor seal or unlevel curb leads to:
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Leaks
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Noise
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Vibration
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Efficiency losses
Roof prep is one of the most underappreciated steps—but critical.
Step 5: Duct Transition Alignment
If the new unit doesn’t line up perfectly with the existing duct openings (most don’t), the crew must:
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Install transition sheet metal
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Remove or adjust existing duct boots
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Adjust return drop
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Realign supply trunk
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Seal and insulate seams
This is where experience pays off.
Good sheet metal work improves airflow.
Bad sheet metal work destroys it.
Here’s a conceptual guide on commercial duct transitions :
[Duct Transition Design Basics]
Step 6: Crane Lift – Installing the New RTU
Now the new 10-ton unit gets its moment.
The crane operator and rooftop crew work in sync:
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Crane lifts the new RTU
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Crew guides it into position
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The crane holds the unit suspended
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Rooftop installers align the frame
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The unit is lowered gently
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Bolts are inserted as the crane maintains slight tension
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The crane releases once secure
Precision matters here.
If the unit drops too hard or lands off-center, the curb seal is compromised.
This is the “make or break” moment of the install.
Step 7: Reconnecting Gas, Electrical & Controls
Once secured:
Electrical Work
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Install new disconnect (if needed)
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Verify voltage and phase
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Pull new conductors if required
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Land connections on terminal block
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Install conduit
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Perform torque checks
Gas Line Work (if gas heating)
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Reroute line as needed
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Install or adjust shutoff valve
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Install drip leg
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Check for code compliance
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Leak-test the entire system
Here’s a conceptual resource on gas appliance pressure parameters:
[Gas Line Routing & Pressure Guidelines]
Control Wiring
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Thermostat integration
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Economizer wiring
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Sensor location verification
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Low-voltage connections
A commercial RTU without correct control wiring is just a fancy rooftop decoration.
Step 8: Charging, Testing & Commissioning
This is the part the building never sees but benefits from the most.
Commissioning includes:
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Verifying refrigerant levels
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Measuring superheat/subcooling
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Checking supply/return air delta
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Blower speed verification
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Static pressure measurement
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Economizer setup and calibration
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Gas pressure tuning
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Burner safety checks
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Running full cooling/heating test
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Checking drain operation
A rooftop unit MUST run through a complete cycle before the crew leaves.
[Commercial HVAC Startup Checklist]
This ensures:
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Proper airflow
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Safe operation
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Correct temperature drop
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Efficient part-load behavior
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Long equipment lifespan
Skip commissioning and the unit may never perform correctly.
Step 9: Roof Sealing, Closing & Cleanup
Once the unit is operational, the team:
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Applies weatherproof roofing sealant
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Seals all penetrations
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Reflashes curb connections
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Tests for water tightness
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Removes old sealant debris
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Cleans roof around work area
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Secures the ladder/hatch
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Removes all tools and rigging
If this step is rushed, you’ll have roof leaks within months.
Step 10: Final Walkthrough, Documentation & Handover
At the end of installation day, the contractor provides:
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Warranty details
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Installation report
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Commissioning data
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Voltage and amp readings
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Refrigerant charge data
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Filter sizes
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Maintenance recommendations
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Safety instructions
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Thermostat programming basics
This final step ensures the building owner or facility staff knows how to operate and care for the new 10-ton unit.
What Can Go Wrong on Installation Day (Tony’s List)
Trust me—I’ve seen it all.
1. Crane delayed due to weather
Wind over 20–25 mph = no lift.
2. Curb adapter arrives wrong
Now you're delaying the job days or weeks.
3. Electrical doesn’t match the new unit
Breaker too small? Wrong wire gauge? Get ready for extra costs.
4. Gas line not up to code
You’re not turning on heat today.
5. Return or supply opening mismatch
Sloppy transitions ruin airflow.
6. Roof not level
Unit sits crooked, drains incorrectly, vibrates excessively.
7. Controls incompatible
Old thermostat can’t handle new logic.
8. Rain or storms
Roof becomes unsafe—and installation pauses.
If you’re prepared?
Smooth day.
If not?
Buckle up.
What a Proper 10-Ton RTU Install Actually Achieves
A correct rooftop installation gives you:
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Higher energy efficiency
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Lower utility bills
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Better temperature control
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Lower humidity
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Quieter operation
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Fewer repairs
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Longer unit lifespan
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Safe and reliable operation
A good install can extend lifespan by years.
A bad one can destroy a unit in a season.
Tony’s Final Verdict
A rooftop HVAC install is far more than swapping boxes. It’s a coordinated, technical, safety-heavy, precision-based process involving multiple specialists. And when it’s done well? Your building runs smoothly, comfortably, and efficiently for a decade or more.
When it’s done poorly?
You’ll be on the roof every summer.
A 10-ton rooftop replacement is one of the biggest service events your building will ever face. Know what’s coming. Budget correctly. And hire a crew that actually knows what they’re doing.
Because once that crane shows up?
There’s no turning back.
Now, let's know how long this unit lasts.
