Rooftop Units
How a Commercial Rooftop Unit Works
The cabinet on your roof, section by section (airflow, refrigeration, heat, controls), and what each part tells a facility team about risk.
5 min read · Read →
Make the HVAC call before it becomes one
Commercial HVAC Learning Center for multi-site facility managers
Interactive tools and guides for the people responsible for dozens of rooftops. They follow the way decisions happen: learn what is going on, compare the options, then act.
01 Learn
02 Compare
03 Act
Live · rooftop conditions
What your rooftops are working against right now
Condensing pressure tracks outdoor ambient, and a dark roof deck runs 15–25°F above the weather number. Pick a county and the reading below translates current conditions into what your units are actually fighting this hour.
- Air temp
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- Feels like
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- Humidity
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How the scale is set: bands read off the higher of air and feels-like temperature — Low <80°F · Elevated 80–94°F · High 95–104°F · Critical 105°F+ — against typical packaged-unit design ambients. Guidance from public weather data, not a measurement of your equipment.
Condenser stress
Reading current conditions…
Checking the live feed for this county.
Two-minute self-check
Is your portfolio ready for peak season?
Six checks, weighted by how much each one actually moves reliability through a Southern California or Arizona summer. Answer all six for a live 0–100 score and a prioritized fix list. No email required.
Is every site on a scheduled maintenance program (ASHRAE 180 or equivalent)?
A documented task list per site, not run-to-fail
Are filters and belts changed on a schedule, not on failure?
Sized to each site's runtime, not one template
Do you have a current asset register (model, serial, tonnage, install date per unit)?
The input every replacement forecast depends on
Is the average unit age across the portfolio under about 12 years?
Commercial units are commonly planned on a service life in the mid-teens of years
Is there a written emergency escalation path, including a temporary-cooling plan?
Who calls whom, and what happens if parts are on back order
Have condenser coils been cleaned within the last 12 months?
Dirty coils are the quiet capacity killer on hot roofs
Readiness score
0 / 100
Answered 0 of 6. Answer every check for the full picture.
How the score works: each check is weighted by its real effect on season reliability. The weights total exactly 100, so the score is a percentage.
Right-size it
RTU tonnage estimator for a retail sales floor
Retail runs roughly one ton of cooling per 350 square feet of sales floor, then moves with ceiling height and what the space is doing. Oversizing is not a safety margin — it short-cycles, dehumidifies badly, and dies younger.
20,000 sq ft
2,000 100,000
Estimated cooling capacity
57 tons
≈ 684,000 BTU/hr
Typically split across multiple rooftop units.
A ballpark only — zoning, exposures, outside-air requirements, and code all move the real number. We confirm with a load calculation against the actual site before anything is quoted. We replace rooftop units up to 100 tons and split systems up to 60.
Repair or replace?
Repair-or-replace check for a single rooftop unit
The honest math: commercial rooftop units are commonly planned on a service life in the mid-teens of years when maintained, and a large repair late in that range usually favors replacement. Four questions, no email wall.
Our read
Answer the four questions
An honest, no-pressure verdict appears here — the same call we would make standing on the roof with you.
Built on a mid-teens planning service life for maintained commercial equipment. A unit-level asset evaluation confirms the call before any money moves.
Regional physics
Dry heat is a different animal
The same rooftop unit behaves very differently in Santa Monica, San Bernardino, and Phoenix. Drag the afternoon and switch regions — the drawing shows what the unit is actually dealing with, and why we structure maintenance differently in each market.
108°F
80°120°
Seasonal recommendation
Call 1-800-742-0910- Roof-deck temp
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- Effective capacity
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- Runtime duty
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- Failure pressure
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What gives out first
- Run capacitors
- Condenser fan motors
- Contactors
- Compressor overload trips
Rule-of-thumb physics, honestly applied: packaged units are rated at 95°F ambient; condensing capacity falls roughly 1% per °F above that, and a dark single-ply roof deck runs 15–30°F hotter than the air. Failure thresholds are typical, not rated values. Not a measurement of your equipment.
01 · Learn
Four decades of rooftop units — we worked through all of them
The unit on your roof has been reinvented three times since 1987. Walk the eras — the drawing gains what each one added, and the right-hand column is what REE was doing at the time.
Typical new-unit efficiency
SEER 9
- Refrigerant
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- Efficiency
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- Controls
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What changed on the roof
What REE was doing
Why it matters: the techs who serviced R-22 machines, absorbed the 410A transition, and maintain today's BMS-connected fleets are the same bench — trained weekly, in house — now handling the A2L changeover on your roofs.
The clock is running
Store-down comfort clock: how a sales floor heats up, minute by minute
Losing cooling is not just uncomfortable — the sales floor gets hotter every minute, and shoppers and staff respond. Set the store, pick the moment it fails, and let the clock run.
50%
- 82° Browsing time shortens; the first shoppers leave early
- 86° Staff rotating to the back; complaints reach the manager
- 90° Comfort is gone; the store is trading on the weather now
The model, in the open: an illustrative heat-gain curve from 78°F toward 95°F, steeper on busy, hot trading windows and when more of the roof is down. Milestones are typical comfort responses, not measurements. There are no dollar figures here: what an hour of downtime means for your stores is your number.
Sales-floor temperature
elapsed 0:00
78°F
and climbing since the compressor quit · 82°F in about — minutes
What shortens the wait
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01
Learn
Understand the equipment on your roofs
How rooftop units, split systems, heat pumps, fan coils, ventilation, and controls actually work, written for the people who approve the work orders.
Rooftop Units
RTU Tonnage: How Retail Sales Floors Are Sized
Why square-feet-per-ton shortcuts mislead, which loads drive a sales-floor design, and when an existing store should be re-checked before replacement.
4 min read · Read →
Rooftop Units
Economizers on Retail Rooftop Units, Explained
How economizer dampers, actuators, and sensors work together, why they fail silently, and what to ask your maintenance provider to verify.
4 min read · Read →
System Types
Packaged vs Split Systems in Commercial Buildings
Where each system type shows up in a commercial portfolio, how they differ for service and replacement, and what facility teams should track for each.
4 min read · Read →
System Types
Water-Source Heat Pumps: How They Work
The loop, the units, and the central plant: how water-source heat pump systems work and where they need attention in an occupied building.
4 min read · Read →
System Types
Hydronic Fan Coils: What Facility Teams Should Know
Two-pipe vs four-pipe, valves and condensate, and the maintenance items that keep fan coils from becoming ceiling leaks in occupied space.
4 min read · Read →
Ventilation
Make-Up Air and Exhaust Balance in Retail Stores
Negative pressure, slamming doors, drifting odors, and struggling RTUs: what exhaust imbalance looks like in a store and how it is corrected.
4 min read · Read →
Controls
Building Management Systems for Multi-Site Portfolios
Schedules, setpoint enforcement, alarms, and trend data: what a BMS gives a regional facility team, and how to plan an upgrade without disruption.
4 min read · Read →
Reference
Commercial HVAC Glossary for Facility Managers
From BACnet to tonnage: plain definitions of the terms that show up on work orders, proposals, and maintenance reports.
5 min read · Read →
02
Compare
Weigh the options before the decision is urgent
Repair or replace, evaporative or refrigerated, reactive or preventive, quarterly or semiannual: the factors that decide each call.
Decisions
Repair or Replace a Rooftop Unit: The Decision Factors
Age, failure type, repair history, refrigerant, efficiency, and disruption: a consistent way to make the call unit by unit across a portfolio.
4 min read · Read →
Decisions
Evaporative vs Refrigerated Cooling in Desert Climates
Where evaporative cooling earns its keep, where it falls short during monsoon humidity, and how water, upkeep, and space use shape the choice.
4 min read · Read →
Maintenance Strategy
Reactive vs Preventive Maintenance: What Each Costs a Store
Beyond the invoice: the operational cost of each model to a store team, including disruption, staff time, decision quality, and the records left behind.
4 min read · Read →
Maintenance Strategy
Quarterly vs Semiannual PM Visits for Retail
Climate, filter loading, runtime, and equipment age: how to set visit frequency per site rather than one interval for the whole portfolio.
4 min read · Read →
Decisions
Ductless Mini-Splits vs RTU Zoning for Small Spaces
Server closets, offices, exam rooms, and additions: how to choose between a dedicated mini-split and changing what the rooftop unit delivers.
4 min read · Read →
03
Act
Put the plan in place, site by site
Checklists and step-by-step guides for roof access, asset registers, peak-season readiness, onboarding, and the hour after a unit fails.
Site Readiness
Preparing a Store for a PM Visit: Roof Access and Site Docs
Roof hatches, ladders, keys, landlord escorts, and the site file: the checklist that keeps a scheduled visit from turning into a return trip.
4 min read · Read →
Portfolio Management
Building an HVAC Asset Register for a Store Portfolio
The fields to capture, how to tag units on the roof, and the habits that keep a register accurate enough to plan capital against.
4 min read · Read →
Site Readiness
Peak-Season Readiness Checklist for Southern California and Arizona
What to complete before the hottest months across coastal, inland, and desert sites: equipment checks, controls, and a contingency plan.
4 min read · Read →
Emergency Response
What to Do When an RTU Fails During Business Hours
The first hour, step by step: what store staff can safely check, what to report, how to protect people and stock, and when to plan temporary cooling.
5 min read · Read →
Portfolio Management
Onboarding a New Store into a Maintenance Program
New openings, acquisitions, and transfers from another provider: the sequence that gets a store from address to maintained asset.
4 min read · Read →
Equipment Care
Coil Cleaning and Condenser Care Between PM Visits
Why coils foul, the warning signs that show up before a failure, and when interim cleaning is worth adding to a site's schedule.
4 min read · Read →
Looking for commentary on budgets, standards, and the refrigerant transition? That lives on the blog.
Read the blogTalk through a commercial HVAC question with REE
Send us your site list and the question you are weighing. We will be straight with you about fit, including when the answer is that you do not need us yet.
- Service & dispatch
- 1-800-742-0910
- service@reehvac.net
Monday - Friday: 7:00 AM - 4:00 PM · 24/7 emergency dispatch
Choose a lane
- Something is down now Emergency service: the nearest technician, not the next available truck from the yard.
- Evaluating a provider Send your site list and we will map it against where our technicians already are.
- Fixing a maintenance program Scoped to ANSI/ASHRAE/ACCA Standard 180, with the reporting trail attached.