How many apprentices can each licensed plumber or HVAC tech supervise? (state ratios)

An apprentice supervision ratio caps how many apprentices one licensed journeyworker can have working under them at once.

It is the rule that decides whether adding two helpers to a crew is a training decision or a violation.

Three different rule-makers can set the number, and which one binds depends on the job and on whether the apprentice is individually registered.

A state licensing board writes job-site ratios into the licence rules for trades it licenses individually.

The registered apprenticeship system works differently: the federal rule requires each program's standards to state a numeric apprentice-to-journeyworker ratio, consistent with proper supervision, training, safety and continuity of employment — but the federal rule itself sets no specific number.

The program picks one.

So the answer to "how many apprentices can my tech supervise?" is never one number.

It is a lookup in three places: your state board's rules, the apprentice's program standards, and — if the job is federally funded — the Davis-Bacon rules covered below.

This page walks each one, trade by trade, with the caps our research verified.

Plumbing is where board-set ratios are most common, because states that license plumbers individually — apprentice or trainee through journeyman and master — tend to write a number into the licence rule.

The job-site caps our research verified:

State	Job-site supervision rule
Alabama	One journeyman or master for up to five apprentices on residential jobs; up to three apprentices on non-residential jobs.
Illinois	A licensed plumber may sponsor or supervise no more than 2 licensed apprentice plumbers at once; supervising 2 requires one of them to have at least 2 years as a licensed apprentice.
Maine	A master or journeyman plumber may directly supervise no more than 3 trainee plumbers.
Michigan	Direct on-site supervision is limited to 1 journey or master plumber per 2 registered plumbing apprentices, on all plumbing work (MCL 339.6117a, effective April 2, 2025).
New Mexico	For unregistered apprentices: one journeyman to two apprentices on commercial/industrial work, one to three on residential.
North Dakota	No more than five plumber's apprentices per supervising master or journeyman plumber on a project.
Oklahoma	Three apprentice plumbers per licensed plumber.
New York	Registered-program ratios: Plumber (60 months) 1:1; 1:3 — Plumber (Pump and Tank) (48 months) 1:1; 1:4.

New York's notation reads differently from a plain fraction.

Under a 1:1; 1:3 entry, one journeyworker supervises the first apprentice, and each additional apprentice adds three more journeyworkers to the requirement.

A program ratio like that is written into the registered standards, not improvised on the site.

Other states set a supervision standard without a number, and those bind just as hard.

Texas lets a Plumber's Apprentice do plumbing only under direct supervision, which the state defines as a TSBPE licensee on the job site at all times.

New Jersey requires plumbing apprentices to have constant on-site supervision by a licensed master plumber or a supervisory journeyman.

Washington requires plumber trainees to work under the direct supervision of a certified plumber, and Minnesota requires unlicensed workers to be directly supervised at all times by a licensed journeyworker or master.

In a supervision-only state the licensed person cannot leave the site — which can cap a crew harder than a numeric ratio would.

HVAC ratios are harder to tabulate for a structural reason: only about a quarter of jurisdictions (13, counting DC) license HVAC workers at an apprentice/technician/journeyman rung at all.

The rest license contractors only, license the master level only, split HVAC work into fuel-gas, refrigeration and electrical pieces, or leave licensing to cities.

Where no worker licence exists, no board sets an apprentice ratio — what remains is the contractor licence, the registered program, and the job's funding rules.

Where HVAC-side numbers do exist, these are the ones our research verified:

State	Job-site supervision rule
Oklahoma	A maximum of 3 apprentices under the direct supervision of one licensed mechanical contractor or journeyman.
New Mexico	For unregistered apprentices: one journeyman to two apprentices on commercial/industrial work, one to three on residential.
New York	Registered-program ratios: Heating, Ventilation & Air Conditioning Mechanic (48 months) 1:1; 1:3 — Refrigeration & Air Conditioning Mechanic (48 months) 1:1; 1:3.
Massachusetts	Refrigeration and pipefitter apprenticeship sponsors must keep the apprentice-to-journeyperson ratio set when the program was registered with the Division of Apprentice Standards (DAS).

Without a numeric cap, states still write supervision standards for HVAC workers:

• District of Columbia — refrigeration/AC apprentices must work only under the direct personal supervision of a licensed master mechanic.
• Delaware — apprentices, journeymen and mechanics may do HVACR work without their own licence when supervised by a Master HVACR licensee who is their employer or works full time for the same business.
• Idaho — an HVAC apprentice may do HVAC work only under the supervision of an HVAC journeyman or contractor.
• New Jersey — an unlicensed HVACR worker with less than 2 years of experience needs constant on-site supervision by a master HVACR contractor or an HVACR journeyperson with at least 5 years; preventive-maintenance workers with 1 year or more need only daily contact.
• Texas — anyone who assists a licensed air conditioning and refrigeration contractor with maintenance or repair work must hold at least a TDLR technician registration. That is a registration requirement rather than a ratio, but it is the rule that decides who can touch the job.

The pattern for an owner: in most of the country your HVAC supervision obligations come from the contractor licence and the registered program, not from an apprentice board rule — so check those two before you assume a number exists.

"Supervision" is not one standard.

States define it at different intensities, and the definition changes what your licensed tech must physically do to keep a crew legal.

Direct supervision is the strict tier.

New Mexico defines it precisely: a certified journeyman working in immediate proximity, overseeing all work as it occurs.

Texas defines it as a TSBPE licensee on the job site at all times.

DC's rule for refrigeration/AC apprentices says direct personal supervision of a licensed master mechanic.

General supervision is the looser tier.

Wisconsin requires plumbing apprentices to work under the general supervision of a licensed master plumber — and the state's DWD Bureau of Apprenticeship Standards sets additional supervision standards for plumbing apprentices beyond the DSPS rules.

New Hampshire runs a progression: direct supervision by a licensed master plumber for the first 2 years, then general supervision for the remaining years (Mec 306.01).

States also carve middle grounds between the two.

Washington's HVAC/refrigeration electrical specialty requires 4,000 hours of supervised experience with supervision at least 75% of the time, while the restricted 6B specialty requires 2,000 hours with 100% supervision until the exam.

South Dakota lets an apprentice plumber who has passed the commission exam and logged 3,800 hours under a contractor work without immediate supervision on single-family dwellings.

North Dakota's version: after 5,700 hours (three years), an apprentice working for a master plumber may work alone in the fourth year.

Federal rules add their own supervision conditions on top.

Apprentices are exempt from EPA Section 608 certification only while they are closely and continually supervised by a certified technician — the supervising technician and the apprentice share responsibility for compliance, and the rule sets no time limit on the exemption.

And apprentices aged 16–17 in registered programs may do some work otherwise barred by child-labor Hazardous Orders only if it is incidental to training, intermittent, for short periods, and under direct and close journeyman supervision.

Read your own state's definition before you staff to a number.

A 1:2 rule under a direct-supervision definition and a 1:2 rule under general supervision are different staffing commitments.

Federally funded or assisted construction contracts over $2,000 fall under the Davis-Bacon and Related Acts, which require contractors and subcontractors to pay workers at least locally prevailing wages and fringe benefits.

On those jobs, apprentice supervision is governed by federal rules that sit on top of your state's:

• Registration first. On a Davis-Bacon job, an apprentice may be paid below the journeyworker wage-determination rate only if they are individually registered in a program registered with DOL's Office of Apprenticeship or a recognized State Apprenticeship Agency.
• The program's ratio caps the site. The apprentice-to-journeyworker ratio in each craft may not exceed the ratio in the registered program. If the crew works outside the program's home locality, the ratio and wage percentages of the project's locality apply.
• The cost of getting it wrong. An apprentice working above the allowed ratio — or not registered at all — must be paid the full wage-determination rate for the work performed. The overage does not just raise a citation; it reprices the hours.

States add their own layer: "little Davis-Bacon" prevailing-wage laws cover state and local public works with their own thresholds and rates.

Those thresholds live in each state's rules — confirm them with the state before you staff a public job.

How the wage rates themselves are determined is its own subject; this page stays on the ratio and registration rules.

For staffing, the ratio is arithmetic on your licensed bench: each licensed journeyworker on a job buys a fixed number of apprentice slots, and no amount of hiring on the apprentice side adds capacity the licensed side does not have.

At Michigan's cap of 1 journey or master plumber per 2 registered plumbing apprentices, every licensed plumber you put on a job carries at most 2 apprentice slots.

Illinois works at the same 2 — with the extra condition that supervising 2 requires one of them to have at least 2 years as a licensed apprentice.

Alabama's residential cap of five apprentices per journeyman or master is the loosest plumbing rule we verified; its non-residential cap is three.

North Dakota counts per project: no more than five plumber's apprentices per supervising master or journeyman plumber.

Two caps stack, and both are yours to track.

The board's job-site ratio governs the site; the registered program's ratio governs the apprentice.

Illinois adds a program-level ceiling: an approved apprenticeship program may not sponsor more licensed apprentices than 2 times the number of licensed plumbers available to supervise them.

Massachusetts ties sponsors to the ratio set when the program was registered — so if you hire from a registered program, its ratio follows the apprentice onto your site alongside your board's rule.

On Davis-Bacon jobs the enforcement lands in the pay rate: an apprentice above the allowed ratio, or not registered, must be paid the full wage-determination rate for the work performed.

Budget the crew before the mobilization, not after the certified payroll.

Once the ratio math is set, the people side — sourcing, screening, pay plans — is our guide to hiring HVAC and plumbing techs.

This page is employer career and business information, not legal advice. Supervision ratios are set by state licensing boards, registered program standards and federal agencies — confirm the rules that apply to your jobs with your state board, the program sponsor, and the DOL Wage and Hour Division before you staff.