A journeyman plumbing license qualifies you for general residential and commercial work — but it's a floor, not a ceiling. Several specialty tracks layer additional certification onto the base license and consistently command a premium over general service work. Here's the map.
Medical Gas Installation
The work: installing and certifying medical gas systems (oxygen, medical air, vacuum, nitrous oxide) in hospitals and healthcare facilities — work with zero margin for error, since these systems are literally life-support infrastructure.
The credential: a specialty certification (commonly ASSE 6010/6020 series or state-equivalent) layered on top of your journeyman or master license, with recertification requirements.
The pay pattern: among the highest-paying specializations in the entire trade — the stakes and the certification barrier both support a real premium, and healthcare construction is steady, non-cyclical demand.
Backflow Prevention Testing and Certification
The work: testing and certifying backflow prevention devices — the systems that stop contaminated water from siphoning back into a clean municipal supply. Required periodically by code on most commercial and many residential properties.
The credential: a backflow tester certification (state or municipal-specific, often ASSE 5110 or equivalent).
The pay pattern: a strong side-specialization or standalone service niche — recurring, code-mandated testing creates dependable repeat revenue, attractive both for employed journeymen and plumbers building toward their own contracting business.
Industrial Steamfitting
The work: high-pressure steam and process piping in industrial, power generation, and large commercial settings — a different physical and technical world from residential drain-waste-vent work, closer in character to industrial pipefitting.
The credential: typically UA-trained, with welding certifications often layered in depending on the specific work.
The pay pattern: among the top-paying corners of the broader "plumbers, pipefitters, and steamfitters" BLS category — a meaningful contributor to why states with heavy industrial pipefitting employment (New Jersey, Illinois) post higher state medians (pay by state).
Water Supply Protection / Cross-Connection Control
The work: broader than backflow testing alone — designing and certifying systems that protect potable water supplies from contamination across complex commercial and municipal systems.
The pay pattern: a natural pairing with backflow certification for plumbers moving toward inspection, code-compliance, or municipal-adjacent work.
| Specialization | Added Barrier | Typical Setting |
|---|---|---|
| Medical Gas | Specialty cert + zero-error stakes | Hospitals, healthcare construction |
| Backflow Testing | Tester certification | Commercial, municipal, recurring service |
| Steamfitting | UA training + often welding certs | Industrial, power generation |
| Water Supply Protection | Cross-connection control cert | Municipal, complex commercial systems |
The base journeyman license opens the door to every house on the block. Each specialty certification on top of it opens a door with far fewer plumbers standing in line — and the pay reflects exactly that scarcity.
See also the related career comparison: Plumber vs. Pipefitter vs. Steamfitter, for how these specialty tracks map onto the broader occupational family.