Rooftop units do the heavy lifting in most commercial buildings across the Permian Basin. Retail centers, office suites, medical clinics, restaurants, and light industrial facilities all depend on packaged RTUs to move conditioned air through the building. Because those units sit out of sight, most of them get attention only when something has already gone wrong.
That habit is expensive. An aging unit quietly adds to your utility spend every month it stays in service, and a mid-July failure puts tenant comfort, inventory, and lease relationships at risk on the hottest day of the year.
Replacing a rooftop unit is a capital decision, not a repair ticket. This guide covers the warning signs that a unit has reached the end of its service life, what a professional installation actually involves from the first roof visit through commissioning, and why the quality of that installation determines how the equipment performs for the next fifteen years.
Signs It Is Time to Replace a Rooftop Unit
Most units give plenty of warning before they fail outright. These signals rarely show up alone. If you recognize two or more, schedule an assessment before the next cooling season rather than during it.
The unit is past its expected service life
Commercial rooftop units are generally engineered for 15 to 20 years of service. In West Texas, the upper end of that range is optimistic. Sustained triple-digit heat, blowing dust that packs into condenser coils, and hard water take years off the practical life of compressors, coils, and cabinet sheet metal. Around year twelve, a unit belongs on your planning list. By year fifteen, it belongs in a capital budget.
Repair spending is climbing year over year
Track cost per unit over a rolling three year window. Once annual repair spend starts approaching a meaningful share of what a new unit would cost, the math has already turned. A useful field rule is to multiply the quoted repair cost by the age of the unit in years. If that number lands above the cost of replacement, you are repairing an asset that no longer justifies it. Replacing a compressor on a unit older than twelve years almost never pays back.
Uneven cooling and recurring tenant complaints
Hot and cold spots across a floor plate, spaces that never reach setpoint on a hot afternoon, and long recovery times after occupancy peaks all get blamed on thermostats and ductwork. Often the real cause is a unit that has lost capacity through fouled coils, a worn compressor, or an economizer damper stuck in the wrong position.
Energy costs rising without a change in occupancy
Compare utility cost per square foot against the same months last year. Equipment built fifteen years ago operates well below current minimum efficiency standards even when it is running perfectly. When it is not running perfectly, the gap widens fast.
The unit runs on an obsolete refrigerant
Equipment charged with R22 is now difficult and costly to service, and the industry has moved on again. R410A is in phasedown, and new commercial equipment is shipping with A2L refrigerants such as R454B. If a technician tells you a refrigerant leak on your unit is not economically repairable, that is usually a supply issue, not a sales pitch.
Cabinet and curb deterioration
Rust along the base rail, a failed curb gasket, standing water inside the cabinet, or roof leaks showing up in the ceiling tile below the unit are structural problems. They shorten the life of everything inside the cabinet and create roofing liability of their own.
The RTU Installation Process, Step by Step
A rooftop replacement combines mechanical, electrical, structural, and roofing work, usually compressed into one or two days. Here is how a properly run project sequences.
Step 1: Site assessment and existing conditions survey
Any contractor quoting your project should be standing on your roof first. A complete survey documents:
- Model, serial, tonnage, and heating type of the existing unit
- Curb dimensions, orientation, and condition, along with the roof deck around it
- Electrical service, disconnect location, and existing overcurrent protection
- Gas supply size and pressure where applicable
- Duct connections and transition condition below the curb
- Control wiring and whether the unit reports to a building automation system
- Crane access, staging area, overhead obstructions, and roof load capacity
Step 2: Load calculations and equipment selection
Replacing like for like is the single most common mistake in this trade. Buildings change. Occupancy shifts, lighting gets retrofitted to LED, insulation improves, partitions move, and tenant improvements alter the whole thermal profile. A commercial load calculation establishes what the space actually requires today.
The cost of getting this wrong runs in both directions. An oversized unit short cycles, dehumidifies poorly, and wears out its compressor early. An undersized unit runs continuously through a West Texas August and never recovers. Selection also settles efficiency tier, number of cooling stages, economizer requirements, gas heat versus electric heat, and controls compatibility with your existing system.
Step 3: Crane logistics and site safety planning
The lift is the highest-risk hour of the entire project, and it deserves a written plan. That plan covers pick weight and radius, crane placement and outrigger loading, overhead power line clearance, ground protection for the parking lot, an exclusion zone below the pick, tag lines, certified rigging, and a designated spotter. It also covers the parts owners care about most: which parking spaces come out of service, how tenants get notified, and whether the lift happens before business hours to avoid disrupting operations.
Step 4: Removal of the existing unit
Work starts with lockout tagout and refrigerant recovery under EPA Section 608 rules. Gas is shut off and capped, electrical is disconnected at the source, and condensate and control wiring are labeled before removal. Duct connections are broken loose, the curb seal is cut, and the old unit is rigged and lifted clear. The open curb and the roof membrane get protected immediately because an unprotected opening and an afternoon storm make for a very bad week. The old equipment leaves the site for recycling.
Step 5: Curb preparation and setting the new unit
With the old unit gone, the curb gets inspected and repaired, and the gasket is replaced. If the new equipment has a different footprint, an adapter curb is fabricated so the duct openings line up correctly and the load transfers properly. The new unit is then set level, with orientation checked for condensate slope and for service clearance on the access panels. Skipping the level check creates drain pan problems that show up as a ceiling stain six months later.
Step 6: Mechanical, electrical, and controls integration
Duct transitions are connected and sealed, gas piping is run and leak tested, electrical is terminated with correct overcurrent protection, and condensate is routed to an approved point of discharge. Sensors, thermostats, and any building automation points are then mapped and verified, and the economizer and outside air linkage are set for the ventilation rate the space requires.
Step 7: Startup, commissioning, and documentation
Commissioning is where a good installation separates itself. A proper startup verifies airflow and external static pressure, confirms refrigerant charge through superheat and subcooling readings, checks amp draw against the nameplate, cycles every stage of heating and cooling, tests safety controls, proves economizer operation, and confirms communication with the building automation system.
Every one of those readings should be written down. Ask for a copy of the startup report and confirm the warranty has been registered with the manufacturer. If a contractor cannot hand you that paperwork, you have no baseline and no proof of proper commissioning.
Why Professional Installation Matters
Warranty protection
Manufacturer warranties on commercial equipment carry conditions. Most require installation and startup by a qualified contractor, correct application of the equipment, and documented commissioning readings. When a compressor fails in year four, the manufacturer will ask for that documentation. An undercharged system or a missing startup report is how a covered claim becomes an owner expense.
Code compliance and permitting
Mechanical, electrical, and gas work on commercial property is permitted and inspected work. Adopted energy and mechanical codes set minimum efficiency, ventilation rates, and economizer requirements for the equipment you are allowed to install. Unpermitted work has a way of surfacing at the worst possible moment, during a sale, a refinance, or an insurance inspection.
Safety and liability
You are authorizing a crane pick over occupied property, work at height, gas piping, and high voltage terminations. Before the project starts, verify the contractor’s general liability and workers’ compensation coverage and confirm current Texas licensing for air conditioning and refrigeration contracting. Ask who is responsible for the roof warranty if the membrane is damaged.
Long-term operating cost
Field studies of installed rooftop equipment consistently find a large share of units operating with charge or airflow faults, quietly giving up efficiency the owner already paid for. Correct charge, verified airflow, sealed duct connections, and a calibrated economizer are the difference between the efficiency rating on the data plate and the efficiency you actually get.
Planning Your Replacement
The best time to plan a replacement is the season nobody is thinking about it. Spring and fall give you equipment availability, crane scheduling flexibility, and the option to do the work outside business hours without an emergency premium. Owners managing several buildings usually do better replacing units in a phased sequence tied to age and repair history rather than waiting for failures to set the schedule.
Once new equipment is in place, a scheduled maintenance program protects the investment. Coil cleaning, filter changes, belt and bearing inspection, and control verification on a set interval are what keep a twenty-year unit from becoming a twelve-year unit in this climate.
Talk to GENMECH HVAC About Your Rooftop Units
GENMECH HVAC is a veteran-owned, family operated commercial HVACR contractor serving Midland, Odessa, Lubbock, and San Angelo. Our technicians bring more than 30 years of combined experience across rooftop units, chillers, boilers, refrigeration, and building automation, and we handle the full scope of a rooftop replacement including assessment, load calculation, crane logistics, installation, and commissioning.
If you are weighing repair against replacement on an aging unit or you are building a capital plan for a portfolio of buildings, call GENMECH HVAC at (432) 528-8905 to schedule a commercial assessment.
Frequently Asked Questions
How much does it cost to install a rooftop unit?
There is no standard figure, because the equipment is only part of the project. Cost is driven by tonnage and efficiency tier, heating type, whether the existing curb can be reused or needs an adapter, crane size and duration, electrical or gas modifications, controls integration, permitting, and whether the work happens during or outside business hours. The only accurate number comes from a site assessment. GENMECH HVAC provides a written scope and quote after evaluating the roof, the existing equipment, and the current load on the space.
How do you install a rooftop AC unit?
The sequence is site assessment, load calculation and equipment selection, crane and safety planning, refrigerant recovery and removal of the old unit, curb preparation, setting the new unit, mechanical and electrical and controls connection, and then startup and commissioning. This is licensed work involving refrigerant handling, gas piping, high voltage, rigging, and roof penetrations. It is not an owner or handyman task, and attempting it typically voids both the equipment warranty and the roof warranty.
How long do commercial rooftop HVAC units last?
Fifteen to twenty years is the general expectation for commercial rooftop HVAC units under normal conditions with consistent maintenance. In West Texas, twelve to seventeen years is more realistic because of sustained heat load and dust accumulation in condenser coils. Units on a regular maintenance program reliably reach the upper end of that range. Units that are only serviced when they fail rarely do.
How much is a 20-ton rooftop unit?
Equipment pricing on 20 ton packaged units varies widely by manufacturer, efficiency rating, heating configuration, and current supply conditions, and the equipment itself is usually a minority of the installed project cost. Crane work, curb adaptation, electrical, controls, and permitting often carry as much weight in the total. Ask any contractor for an installed price with a defined scope rather than an equipment number, because equipment quotes are not comparable across bids.
Conclusion
Replacing a rooftop unit is a planning decision, not an emergency one, and the owners who schedule it in spring or fall get better equipment options, off-hours crane work, and bids they have time to read. Just as important, two identical units set on the same building will not perform the same because efficiency ratings are earned on a test stand and either preserved or lost during commercial HVAC installation. Verified airflow, correct charge, sealed duct transitions, and a documented startup report are what carry the data plate rating into your utility bill. GENMECH HVAC is a veteran-owned, family operated commercial HVACR contractor serving Midland, Odessa, Lubbock, and San Angelo, and our technicians handle the full scope of a replacement from roof assessment and load calculation through crane logistics, installation, and commissioning. If you are weighing repair against replacement on an aging unit, call GENMECH HVAC at (432) 528-8905 to schedule a commercial assessment.
