Chilled Water Pipe Marking: Colors, Labels, and Code Requirements
Chilled water systems are one of the most common pipe systems in commercial and industrial buildings. They're in every HVAC system, every data center, every hospital mechanical room.
And they're one of the most frequently mislabeled — or unlabeled — pipe systems on any job site.
This guide covers the correct pipe marker colors, label text, and placement rules for every chilled water pipe type. Whether you're marking a new installation or bringing an existing system into compliance, this is your go-to reference.
What Is a Chilled Water System?
A chilled water system uses cooled water to remove heat from a building. The water is chilled at a central plant (a chiller) and then pumped through the building to air handling units or fan coil units.
The main pipe circuits in a typical chilled water system are:
- Chilled water supply (CHWS) — cold water leaving the chiller heading to the building loads
- Chilled water return (CHWR) — slightly warmer water returning to the chiller after picking up heat
- Condenser water supply (CWS) — warm water from the chiller heading to the cooling tower
- Condenser water return (CWR) — cooled water from the cooling tower returning to the chiller
- Glycol supply and return — in freeze-prone applications, water mixed with propylene or ethylene glycol instead of plain water
Each of these circuits is a separate pipe system and needs its own pipe markers.
ASME A13.1 Color for Chilled Water Pipes
Under ASME A13.1, chilled water is classified as a safe fluid — it's non-hazardous, non-flammable, and operates at low pressure relative to steam systems.
The correct color for chilled water pipe markers is:
Green background — White text
This applies to:
- Chilled water supply (CHWS)
- Chilled water return (CHWR)
- Condenser water supply (CWS)
- Condenser water return (CWR)
- Makeup water lines feeding the system
All are safe fluids under ASME A13.1 and use green/white markers.
What About Glycol Loops?
Glycol is where it gets a little more nuanced.
Propylene glycol (the food-safe type used in most HVAC applications) is classified as a safe fluid under ASME A13.1. Use green/white markers.
Ethylene glycol (more toxic, used in industrial and automotive applications) is classified as a hazardous material under ASME A13.1. Use yellow/black markers.
If you're not sure which glycol is in the system, check with the mechanical engineer or the system documentation. Using the wrong color — especially putting green markers on an ethylene glycol line — is a real safety issue.
Standard Label Text for Chilled Water Systems
ASME A13.1 doesn't mandate specific wording, but the industry has settled on clear, consistent abbreviations that show up on job after job. Use these and every tech in the field will know exactly what they're reading.
| Pipe | Recommended Label Text |
|---|---|
| Chilled water supply | CHILLED WATER SUPPLY or CHWS |
| Chilled water return | CHILLED WATER RETURN or CHWR |
| Condenser water supply | CONDENSER WATER SUPPLY or CWS |
| Condenser water return | CONDENSER WATER RETURN or CWR |
| Propylene glycol supply | GLYCOL SUPPLY or HGL-S |
| Propylene glycol return | GLYCOL RETURN or HGL-R |
| Ethylene glycol supply | GLYCOL SUPPLY — HAZARDOUS |
| Makeup water | CHILLED WATER MAKEUP or MWUP |
For most commercial HVAC jobs, you'll primarily need CHWS, CHWR, CWS, and CWR. The glycol labels come up in cold climates, process cooling, and specialty HVAC applications.
Flow Direction Arrows on Chilled Water Lines
Every pipe marker for a chilled water system needs a flow direction arrow.
This matters most on chilled water systems because supply and return look identical — they're the same diameter, the same material, and they often run parallel to each other. The only visual clue that tells you which is supply and which is return is the label text and the flow arrow.
An HVAC tech who needs to balance the system, add a flow meter, or make a connection needs to know which direction the water is flowing. Without arrows, they have to guess — or trace the pipe back to the chiller.
At Print Pro AZ, all of our chilled water pipe markers are available with integrated flow direction arrows on both ends. We also stock standalone arrow labels in green/white for adding separately.
→ Shop Green/White Pipe Markers
Pipe Marker Sizing for Chilled Water Systems
Chilled water pipes vary widely in size — from ¾" branch lines feeding individual fan coil units up to 24" or larger mains in central plant rooms.
Use the ASME A13.1 size chart to select the right label:
| Pipe OD | Label Size |
|---|---|
| ¾" to 2" | 8" × 1⅛" |
| 2½" to 7⅞" | 14" × 2¼" |
| 8" to 10" | 24" × 4" |
| Over 10" | 32" × 4" |
On a typical commercial HVAC job, you'll use the 14" × 2¼" label for most branch and main piping. The 8" label covers the small runouts to individual units. Large central plant mains may need 24" or 32" labels.
If your chilled water pipes have insulation — and most do — measure the OD of the insulation jacket, not the bare pipe, and size from there.
Placement Rules for Chilled Water Piping
For chilled water systems specifically, the most important placement locations are:
At the chiller itself — Label supply and return connections at the chiller first. This is the "source" of the system, and label it clearly with both the pipe content and the flow direction.
At the primary/secondary loop connection — Many chilled water systems have a primary loop (chiller to the distribution header) and a secondary loop (distribution header to the building loads). Label at the decoupler or bridge connection.
At every air handling unit connection — CHWS and CHWR connect to every AHU, FCU, and chilled beam in the building. Label at each equipment connection.
At every valve — Isolation valves, balancing valves, pressure independent control valves (PICVs), and butterfly valves all need labels on both sides.
At every branch — When the chilled water main branches off to serve different zones or floors, label each branch takeoff.
At every wall, floor, and ceiling penetration — Label both sides of every penetration.
Every 25–50 feet on straight runs — In mechanical rooms, corridors, and pipe chases, repeat labels at intervals so no stretch of pipe goes unidentified.
Chilled Water vs. Domestic Cold Water: Don't Mix Them Up
One of the most common labeling mistakes in mechanical rooms is confusing chilled water lines with domestic cold water lines.
Both run at cold temperatures. Both use green/white markers under ASME A13.1. The difference is in the label text.
- Domestic cold water: COLD WATER, DCW, or DOMESTIC COLD WATER
- Chilled water: CHWS, CHWR, CHILLED WATER SUPPLY, CHILLED WATER RETURN
If a plumber accidentally taps into a chilled water line thinking it's a domestic cold water line, the results range from inconvenient (glycol contamination) to serious (system pressure problems, water quality issues in a healthcare setting).
Label every line with specific text — not just the color.
What About Pre-Insulated Pipe and Vapor Barrier Jackets?
Chilled water pipes are almost always insulated to prevent condensation. The label goes on the outside of the insulation jacket — not on the bare pipe underneath.
Make sure the label material is compatible with the jacket surface. Most self-adhesive vinyl pipe markers adhere well to standard fiberglass and foam insulation jackets. For unusual jacket materials (foil, canvas, rubber), ask about compatibility when ordering.
For insulated piping, the label size is based on the OD of the insulation jacket. A 4" chilled water pipe with 2" insulation on each side has a jacket OD of about 8" — which puts it in the 24" × 4" label category.
Ready to Mark Your Chilled Water System?
Print Pro AZ stocks all standard chilled water pipe markers in green/white, in all four ASME A13.1 sizes. Same-day shipping. Made in the USA.
👉 Shop All Green/White Pipe Markers → 👉 Need custom text for glycol or specialty systems? Order Custom Markers →
Frequently Asked Questions
What color are chilled water pipe markers? Chilled water pipe markers use a green background with white text under ASME A13.1. Chilled water supply, chilled water return, condenser water supply, and condenser water return are all green/white.
What is the label text for chilled water supply? The most common label text is "CHILLED WATER SUPPLY" or the abbreviation "CHWS." Both are widely accepted. Use whichever matches your facility's existing labeling convention.
What color are glycol pipe markers? Propylene glycol (the common HVAC type) uses green/white markers — same as chilled water. Ethylene glycol (more hazardous) uses yellow/black markers. When in doubt, confirm which glycol is in the system before selecting the color.
Do chilled water pipes need flow arrows? Yes. ASME A13.1 requires flow direction arrows on all pipe systems, including chilled water. This is especially important on chilled water systems because supply and return lines run parallel and look identical without labels.
How often do chilled water pipes need to be labeled? At minimum: at every valve, every branch, every wall/floor penetration, every equipment connection, and at 25–50 foot intervals on straight runs.
What size pipe marker do I need for an insulated chilled water pipe? Measure the outside diameter of the insulation jacket, not the bare pipe. Use that measurement with the ASME A13.1 size chart: up to 2" OD = 8" label, 2½"–7⅞" OD = 14" label, 8"–10" OD = 24" label, over 10" OD = 32" label.
Can chilled water and domestic cold water use the same color marker? Yes — both use green/white under ASME A13.1. This is why the label text is so important. Always use specific text (CHWS, CHWR, COLD WATER, etc.) rather than relying on color alone to identify the pipe.
