Valve Tag Numbering Conventions
There is no single national valve tag standard; numbering comes from the project specification and the valve schedule. This guide covers the conventions most mechanical specs follow — system abbreviations, numbering by floor or area, normal position — plus tag content, size, material, and what to send when ordering.
- Updated
- 2026-10-03
- Length
- 999 words
A valve tag has one job: let someone standing in a mechanical room find the right valve on the schedule, and let someone reading the schedule find the valve. Everything about how tags are numbered follows from that. There is no single national standard for the numbers themselves; the project specification and the engineer's valve schedule set the scheme, and most of them follow a handful of conventions.
Where the numbering comes from
On a commercial or industrial job, valve identification is specified in the mechanical and plumbing identification sections, commonly CSI MasterFormat 23 05 53 (Identification for HVAC Piping and Equipment) and 22 05 53 (Identification for Plumbing Piping and Equipment). The spec describes the tag (size, material, lettering) and requires a valve schedule: a list of every tagged valve with its number, system, location, service, and normal position, posted in the mechanical room and included in the O&M manual.
The contractor normally assigns the numbers against that schedule, and the tags are ordered from it. That is why a tag order usually arrives as a spreadsheet.
Common numbering schemes
System prefix plus sequence
The most common convention. A short abbreviation for the piping system, then a sequence number:
| Prefix | System |
|---|---|
CHWS / CHWR | Chilled water supply / return |
HWS / HWR | Heating hot water supply / return |
CWS / CWR | Condenser water supply / return |
DCW / DHW | Domestic cold / hot water |
CW / HW | Cold / hot water (plumbing shorthand) |
S / HPS / LPS | Steam / high- and low-pressure steam |
CR / PC | Condensate return / pumped condensate |
G / NG | Gas / natural gas |
FP | Fire protection |
CA | Compressed air |
RW / MU | Reclaimed water / make-up water |
So the first chilled water supply valve is CHWS-1 or CHWS-101, and so on. Many specs simply use V- for every valve and let the schedule carry the system: V-101, V-102.
Numbering by floor or area
Larger buildings fold the location into the number so a tag reads where it is:
CHWS-3-07— chilled water supply, third floor, seventh valveV-B-012— basement, valve 12HW-MR2-04— hot water, mechanical room 2, valve 4
The schedule still carries the full location; the number just makes it faster to find.
Starting at 101
Starting sequences at 101 rather than 1 is a habit worth keeping: every number has the same digit count, tags sort correctly in a spreadsheet, and there is room to insert a 100-series valve without renumbering. Three digits covers most buildings; plants go to four.
Leave gaps for additions
A schedule that uses every number in order has nowhere to put the valve added during commissioning. Reserving a block per system, say CHWS-101 to CHWS-199, keeps additions in the right series.
What goes on the tag
The spec decides, but the usual content, in rough order of importance:
- Valve number — the largest lettering on the tag, typically 1/2 in. high on a 2 in. tag.
- System or service —
CHILLED WATER SUPPLY,DOMESTIC HOT WATER, in smaller lettering. - Normal position —
NO(normally open) orNC(normally closed), where the spec requires it. - Optionally: valve size, the equipment or zone it serves, or a drawing reference.
Keep the tag to what someone needs standing in front of the valve. Everything else lives on the schedule.
Tag size, shape, and material
| Attribute | Common choice |
|---|---|
| Shape | Round, 1-1/2 in. or 2 in. diameter; sometimes rectangular |
| Hole | Single hole at the top for chain or wire |
| Attachment | Brass or stainless bead chain, S-hook, or stainless wire; some specs allow nylon ties |
| Material, indoor mechanical rooms | Brass (traditional) or anodized aluminum |
| Material, steam, chemical, outdoor, washdown | Stainless steel |
| Lettering | Engraved or laser-marked; 1/4 in. minimum for the number is a common spec line, 1/2 in. where room allows |
Brass is the historic default and still appears in many specs by name. Stainless is the better choice for anything hot, wet, or outside, and it laser-marks with a dark annealed legend that does not need fill. Anodized aluminum is light, inexpensive, and takes a bright white legend against the color; it suits indoor systems and color-coding by system.
Color coding by tag background (red for fire protection, yellow for gas, and so on) is sometimes specified; anodized aluminum in stock colors handles it. Where the spec requires colored text, that is a printed or filled tag rather than a laser-marked one.
Matching existing tags
On renovation work the new tags should match the building's existing scheme and, ideally, the existing tag style, so the schedule stays coherent. Send a photo and the dimensions of an existing tag along with the new numbers; a vendor can match size, hole, and lettering closely enough that the mechanical room does not end up with two visibly different generations of tag.
Ordering a set
A valve tag order needs very little:
- The list: one line per tag with the number and the service text, straight from the valve schedule. The serial number generator produces a numbered range with a prefix if the schedule only gives you a count.
- Size and shape, material, and hole or slot.
- Normal position or any extra line, if the spec calls for it.
- Quantity, which for a small job may be six.
Tags with different text on each one cost the same as identical tags when they are laser-marked from a list, so there is no reason to simplify the schedule to save money. For short runs with no minimum, see metal tags and legend plates.