How to Number and Label RTUs, Condensing Units & Refrigeration Equipment
Every service call starts the same way: which unit is it? A clear, durable equipment ID on every rooftop unit and condensing unit answers that question for the next tech, the building owner, and the inspector.
Important Disclaimer
This article is provided for general informational purposes only and does not constitute legal, safety, or professional compliance advice. Regulations, standards, and codes are subject to change and may be interpreted differently by authorities having jurisdiction (AHJ). Always consult with qualified safety professionals, licensed engineers, or legal counsel to determine the specific requirements applicable to your facility. TagBuilder is not responsible for any actions taken based on this information.
Why Contractors Label Every Unit
On a commercial roof with six identical packaged units, "the one by the parapet" is not an address. Mechanical contractors label equipment so that maintenance logs, service contracts, and building automation points all refer to the same physical machine. A convenience store with a walk-in cooler, an ice machine, and a beer cave may have a dozen condensing units in one rack — without IDs, warranty claims and refrigerant records get attached to the wrong compressor.
There is a code angle too. NEC 440.14 requires a disconnecting means within sight of air-conditioning and refrigeration equipment, and inspectors expect the disconnect and the unit it serves to be identifiable. When one roof serves multiple tenants, many jurisdictions ask for equipment to be marked with the space it serves.
Standard Numbering Conventions
Most mechanical drawings and CMMS systems use a short prefix plus a sequence number. Keep the scheme boring and predictable — the goal is that a tech who has never seen the site can find the unit.
| Prefix | Equipment | Example |
|---|---|---|
| RTU | Rooftop packaged unit | RTU-1, RTU-2 |
| CU | Condensing unit | CU-4 Ice Machine |
| AHU | Air handling unit | AHU-1 |
| MAU | Makeup air unit | MAU-2 |
| EF | Exhaust fan | EF-3 |
| P / HWP | Pump / hot water pump | P-1, HWP-2 |
Adding what the unit serves — "CU-7 Beer Cave", "RTU-3 Sales Floor" — costs nothing on an engraved label and saves the most time of anything on this page.
Labels That Survive a Roof
A roof is the worst environment a label can live in: direct UV, rain, ice, and 140°F sheet-metal surface temperatures in summer. Printed vinyl stickers and hand-written paint pen both fade or peel within a couple of seasons. Engraved two-ply plastic keeps its contrast because the letters are cut through the cap layer into the core — there is no ink to fade. Black-on-white or white-on-black 4×2 inch plates with 5/16″ characters are readable from a ladder. Choose outdoor adhesive backing for clean cabinet panels, or screw/rivet mounting holes for textured or dirty surfaces.
A Simple Ordering Workflow
List your equipment IDs (RTU-1 through RTU-6, CU-1 through CU-12, and so on), pick one size and color for the whole site, and order the full set at once so every unit matches. Typical turnaround for engraved equipment IDs is days, not weeks, so the labels can go on during the same service visit.
Need equipment ID labels? Our 4×2″ engraved labels ship with your exact text — RTU, CU, AHU, or anything else.
Need custom sizes or multi-line text? Build exactly what you need in the tag configurator.
Photo credits: "Rooftop Packaged Units" (public domain); "Air conditioning units on the roof" by Kgbo via Wikimedia Commons (CC BY-SA 4.0). Product images: TagBuilder.
