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Installing a 6–10 Ton Packaged Unit: What Really Happens on Commercial Install Day

Most business owners think installing a 6–10 ton commercial packaged unit is just:
“Bring a crane, drop it on the roof, hook it up, done.”

Tony laughs every time he hears that.

A commercial install is nothing like swapping out a home AC.
A single mistake with airflow, curb alignment, gas piping, electrical feeds, or economizer sealing can ruin comfort, spike energy bills, or burn out a brand-new system in months.

This is Tony’s real-world, step-by-step breakdown of what actually happens on commercial install day — not the polished version you hear from sales reps.

If you want to know what you're truly paying for, read this start to finish.

1. Pre-Install Prep: The Part Nobody Sees (But Makes or Breaks the Job)

Before a crane ever shows up, Tony’s team completes the real heavy lifting.

✔ Building evaluation

curb size and alignment
return and supply duct locations
electrical panel distance
gas meter location
roof access
building occupancy schedule

✔ Site logistics

blocking off parking lots
setting up lift zones
scheduling crane arrival windows
coordinating with business hours
ensuring roof access meets OSHA requirements

✔ Equipment staging

The new unit arrives 1–2 days before install.
It’s inspected for shipping damage, coil dents, and cabinet warping.
You’d be surprised how often shipping mishandling ruins a rooftop unit.

*(Reference: [Commercial HVAC Job-Site Preparation & Safety Standard])

2. Old Unit Shutdown & Removal — The Dirty Part

Tony powers down the old unit and verifies:

✔ no load on electrical lines
✔ gas valve closed
✔ thermostat circuits safe
✔ economizer disconnected

Then the rooftop teardown begins.

Removal Steps:

disconnect electrical feeds
disconnect gas piping
remove curb adapter if present
pull old unit apart if too heavy to crane out in one piece

Sometimes the old curb is rotted, warped, or water-damaged.
Sometimes duct transitions are leaking like crazy.

Tony never installs a new unit on a bad curb.
That’s a recipe for:

air leaks
water leaks
noise
vibration
short equipment life

*(Reference: [Commercial Rooftop Equipment Removal & Rigging Guidelines])

3. Crane Lift: The Most Expensive 20 Minutes in Commercial HVAC

Crane time is expensive.
That’s why Tony runs this part like a military operation.

Steps:

Lift operator and HVAC foreman sync radios
Traffic is blocked
Tag lines secure the unit
Unit is lifted 30–80 feet
Spotter guides the landing
Unit is set precisely onto the roof curb

Tony measures the curb twice before the lift.
If that packaged unit doesn’t drop perfectly, the ductwork, gas line, and economizer alignment will all fight each other.

Even a ¼-inch misalignment creates:

massive air leakage
temperature imbalance
wasted energy
noise
airflow turbulence

Curb placement is EVERYTHING.

4. Setting the Unit on the Roof Curb (The Make-or-Break Moment)

Once the crane drops the unit, Tony’s team:

✔ checks gasket compression
✔ ensures the unit’s base aligns with supply/return openings
✔ seals gaps
✔ insulates joints
✔ installs vibration pads if needed
✔ bolts down the frame

Any gaps between the unit and curb will suck in dirty attic or outdoor air.
This kills efficiency and comfort.

*(Reference: [Rooftop Curb Installation & Weatherproofing Manual])

5. Connecting the Ductwork — Where 80% of Comfort Problems Start

Commercial ductwork is never perfect.
Tony inspects every inch of the supply and return:

✔ checking for:

collapsed flex
crushed metal
undersized transitions
missing insulation
airflow restrictions
leaky seams

✔ adjustments:

sealing with mastic
adding internal turning vanes
resizing transitions
correcting plenum alignment
improving return airflow

A perfect 10-ton unit with bad ductwork cools like a 6-ton.
Most comfort complaints?
Ductwork, not equipment.

*(Reference: [Commercial Airflow, Duct Sizing & Static Pressure Reference])

6. Gas Line Installation (If Gas Heat Model)

Gas line work must follow strict commercial safety and local code requirements.

Tony:

sizes piping based on BTU load
checks for proper manifold pressure
adds shutoff valves
pressure-tests the line
verifies venting orientation
ensures no leaks

Gas heat failures almost always come from lazy installers who don’t pressure-test.

*(Reference: [Commercial Gas Piping Installation])

7. Electrical Wiring, Disconnects & Breaker Verification

Tony checks:

breaker sizing
conductor gauge
ground integrity
disconnect box rating
economizer wiring
fan/compressor staging wires
thermostat compatibility

Commercial packaged units pull serious amperage.
Wrong wiring = tripped breakers, overheating, and equipment failure.

Electric heat strip models need huge breakers and correct phase balance.

8. Economizer & Fresh Air Intake Setup — The Most Ignored Part of Commercial Installs

Economizers save money…
only if they’re set correctly.

Tony inspects:

damper actuator
minimum position settings
free-cooling mode
mixed-air sensor
outdoor air sensor
barometric relief

Half the units Tony services have economizers stuck open — pulling hot outdoor air into the building all day.

9. Condensate Drain Setup — Often Done Wrong

A mis-sloped drain causes:

ceiling leaks
mold
rust
clogged traps
unit shutdowns

Tony:

sets proper slope
checks trap height
insulates drain lines
secures clamps
tests for flow

Small mistake.
Big problems.

10. System Startup, Testing, and Commissioning

This is where Tony separates a real commercial install from a cheap install.

He verifies:

✔ superheat/subcooling
✔ static pressure
✔ supply air temperature
✔ gas pressure (if gas)
✔ coil performance
✔ blower RPM
✔ amperage on all motors
✔ thermostat staging
✔ economizer logic
✔ exhaust/relief airflow