What is the difference between C-37, R-37 and CR-37?

The Registrar's rules sort licenses into three families. Rule R4-9-102 lists the commercial classifications and is titled "Commercial Contractor License Classifications and Scopes of Work." Rule R4-9-103 does the same for residential, and rule R4-9-104 covers dual licenses. The plumbing entries are:

• C-37 Plumbing in the commercial rules.
• R-37 Plumbing, Including Solar and the R-37R subclasses in the residential rules.
• CR-37 Plumbing in the dual rules.

State law draws the line between commercial and residential by location. Under A.R.S. 32-1101, a commercial contractor does work "except within residential property lines." A residential contractor does work "within residential property lines," including constructing, altering or repairing a residential structure and connecting it to utility service lines, metering devices or sewer lines. A dual licensed contractor works "under a single license on commercial or residential property."

So the class on the license is not a quality grade. It is a boundary on where and what the licensee is allowed to do.

The commercial rule says the C-37 classification "allows the licensee to install, alter, and repair all plumbing when performed solely within property lines and not on public easements or right-of-ways, except as hereinafter provided."

The rule then lists what that includes:

• Piping, fixtures and appliances related to water supply, including pressure vessels and tanks. Municipal or related water supply systems are excluded.
• Venting and sanitary drainage systems for fluid, semifluid and organic wastes.
• Septic tanks and leaching lines, roof leaders and lawn sprinklers.
• Water conditioning equipment, and piping and equipment for swimming pools.
• Piping, fixtures, appliances and pressure vessels for manufactured and natural gases, compressed air and vacuum systems, and petroleum and fuel oil.
• Hot water heating and hot water supply systems operating at pressures not exceeding 30 PSIG or temperatures not exceeding 220 degrees F, and steam systems not exceeding 15 PSIG.
• Gas or oil fired space heaters and furnaces, excluding duct work.

There is one exception to the "within property lines" limit. The rule says sewer, gas and water lines, "and connections from structure to the nearest point of public supply or disposal may cross public or private easements or be installed within private easements or right-of-ways." It adds limits. Pipe installed across public property may not be increased in size or connected to anything else between the point where it leaves private property and the public connection. The lines "shall not be installed parallel to main lines in public easements or right-of-ways."

The residential rule says R-37 "allows the licensee to install and repair water and gas piping systems, fire protection as it relates to water sprinkler systems, and sewage treatment systems." It adds that included are "all fixtures, vents, and devices common to the industry, as well as solar applications," and that the scope "includes all R-37R subclassifications."

That last phrase explains the code you may see on a license, R-37R. The rule lists R-37R Plumbing as a subclassification, along with built-in central vacuum systems, kitchen and bathroom fixture refinishing, swimming pool plumbing and equipment, gas piping, sewers, drains and pipe laying, and solar plumbing liquid systems only. The rule also states that new applications for those narrower R-37R subclassifications, other than R-37R Plumbing, are no longer accepted. So those narrow codes are closed to new applicants, though you may still see them on older licenses.

For a homeowner, an R-37 or R-37R plumbing license fits work on a house, since the state ties residential licenses to work within residential property lines.

The dual rule is short. It says CR-37 Plumbing "allows the scopes of work permitted by the commercial C-37 Plumbing and the residential R-37R Plumbing licenses."

That means a CR-37 licensee holds both scopes under one license. A plumber with a dual license such as CR-37 can take a home repipe on Monday and a restaurant restroom on Tuesday without a second license. Under A.R.S. 32-1101, a dual licensed contractor may work on "commercial or residential property" under a single license.

If you manage property that mixes uses, such as a mixed-use building or a home with a separate commercial unit, a CR-37 license is the class that covers both without asking two contractors to split the job.

What are the C-77, CR-77 and C-78 codes? You may also see a 77 or a 78 in place of the 37.

• C-77 Plumbing Including Solar in the commercial rules covers plumbing "including solar," with the same property-line limits as C-37.
• CR-77 Plumbing Including Solar in the dual rules combines C-77 with the residential R-37 Plumbing, Including Solar license.
• C-78 Solar Plumbing Liquid Systems Only covers solar water heating systems operating at temperatures not exceeding 220 degrees F, including collectors, storage and expansion tanks, heat exchangers, piping, valves, pumps and sensors, and it excludes all non-solar plumbing.

If a solar water heater is part of your project, ask which class the contractor holds.

Does one license cover everything a plumber does? Mostly, but not always. Under A.R.S. 32-1121(B), a person licensed in a trade does not need a separate license for mechanical or structural service work within the scope of that trade. Work outside the trade's scope is a different matter. For example, the C-37 scope excludes duct work for furnaces, and the property-line and easement limits above still apply.

Use the class as a checklist, not a guarantee.

1. 1House or condo: look for R-37, R-37R Plumbing or CR-37. The residential and dual families are written for work on residential property, while the statute defines commercial work as work outside residential property lines. Ask what class the plumber holds if the job is unusual.
2. 2Restaurant, store or office: look for C-37 or CR-37. A residential-only license is written for work within residential property lines.
3. 3Mixed property: look for CR-37.
4. 4Solar water heating: C-77 and C-78 are commercial classes. For a house, ask about R-37, which includes solar, or CR-77.

Then check the license itself. Our page on how to verify a plumber's ROC license in Arizona shows where to search and what to confirm, including the license class and status. If you are still deciding whether the job needs a licensed contractor at all, see whether you can do your own plumbing in Arizona.

Ask any plumber for a license number and class before you hire, and ask us too. We are licensed and insured, we give free estimates, and you get the price up front.