1.5 Scope of the Law, Heating Boiler Exclusion & Portable Equipment
Key Takeaways
- Under Title 6.5, providing stationary engineer services means overseeing a power plant, plant of machinery, or boiler generating pressure above 15 PSI and operating at 30 HP or greater; hot water boilers exceeding 160 psig or 250°F are also regulated.
- Heating boilers are excluded from licensing when steam is ≤15 psig, or hot water is ≤160 psig and ≤250°F (§6.5-101(d)/(f)(2); Board FAQ).
- License grade is based on the largest single regulated object’s horsepower and pressure — not plant aggregate (Board FAQ Horsepower Determination).
- Portable or leased boilers still require the appropriate Maryland license if otherwise regulated.
- Maryland has statewide licensing since 2005, complaint-driven enforcement, and no reciprocal exam waiver with other states.
Scope of the Law: Who Must Be Licensed?
Maryland regulates people, not just equipment. The statutory trigger is whether someone is providing stationary engineer services under Title 6.5 of the Business Occupations and Professions Article. Exam questions regularly mix three ideas that must stay separate: (1) what work requires a license, (2) which boilers are excluded as heating equipment, and (3) how the Board assigns a license grade once licensure is required.
What Counts as Providing Stationary Engineer Services
A person provides stationary engineer services when they oversee:
- A power plant
- A plant of machinery
- A boiler generating pressure more than 15 PSI and operating at 30 horsepower (HP) or more, or a hot water boiler operating above 160 psig or above 250°F
Board FAQs also confirm the law's reach includes equipment such as chillers, refrigerators, motors, generators, compressors, pumps, and related systems that create hazards if not operated safely — not boilers alone. The phrase plant of machinery is broader than a single boiler room. A campus central plant with steam boilers, chilled-water machines, combustion air fans, fuel oil pumps, and condensate return equipment can be one regulated operational unit when a licensed person has charge.
| Equipment type | Regulated for operator licensing when… | Typical excluded heating example |
|---|---|---|
| Steam boiler | Pressure > 15 PSI and rating ≥ 30 HP | 10 psig building heat boiler |
| Hot water boiler | Pressure > 160 psig or temperature > 250°F | 30 psig / 180°F heating unit |
| Plant of machinery | Person has charge of integrated regulated plant machinery | Standalone low-pressure heater only |
| Large chiller / refrigeration compressor | Meets Title 6.5 pressure and HP thresholds | Small packaged unit below thresholds |
Heating Boiler Exclusion — Read Both Limits
Heating boilers are specifically excluded from the definition of providing stationary engineer services. Per statute (§6.5-101(d)/(f)(2)) and the Board FAQ:
- Steam heating boilers at 15 psig or less are excluded
- Hot water heating boilers at 160 psig or less and 250°F or less are excluded
For hot water, both pressure and temperature limits must be met for exclusion. A 150 psig / 260°F unit is not excluded because temperature exceeds 250°F. A 170 psig / 220°F unit is not excluded because pressure exceeds 160 psig. A 140 psig / 230°F unit is excluded because both limits are satisfied.
Exclusion from operator licensure is not an inspection holiday. Low-pressure heating boilers may still require Certificates of Inspection under the Boiler and Pressure Vessel Safety Act and COMAR 09.12. An owner can have compliant inspected equipment and still need a licensed engineer if a separate high-pressure object or plant-of-machinery duty exists on site.
Worked Scenarios: Exclusion vs Licensure
| Scenario | Analysis | License required? |
|---|---|---|
| 12 psig steam, 45 HP district heating boiler | Steam ≤15 psig → heating exclusion | No (for operator licensure) |
| 155 psig / 265°F hot water heater | Temperature >250°F | Yes — not a heating exclusion |
| 200 psig / 240°F process hot water generator | Pressure >160 psig | Yes |
| Building with excluded heating boilers plus one 90 HP steam boiler at 125 psig | Regulated object present | Yes — Grade 4 band (any building) |
Largest Single Piece of Equipment (Not Aggregate)
The Board FAQ titled Horsepower Determination answers a direct question — is grade based on the sum of all equipment HP? No. Grade is based on the horsepower and operating pressure of the largest, single piece of equipment in the plant, not combined totals, power source, or unrelated facts. The official Notice to Owners and Operators repeats the same rule.
| Plant situation | Controlling object | Minimum grade |
|---|---|---|
| Four 90 HP boilers on one header (360 HP total) | Largest unit = 90 HP | Grade 4 (30–99 HP, any building) |
| One 500 HP boiler plus several 50 HP auxiliaries | Largest unit = 500 HP | Grade 1 (500+ HP) |
| Three 125 HP boilers manifolded | Largest unit = 125 HP | Grade 3 (100–299 HP) |
If an operator incorrectly adds manifolded boilers to claim aggregate plant HP, they will overstate the required grade. The Board's answer to the aggregate question is a clear No.
Portable, Leased, Temporary, and Out-of-State Equipment
Portable or leased boilers still require an appropriate Maryland license if otherwise regulated. Temporary installation, rental company ownership, or jobsite mobility does not waive Title 6.5. A leased 45 HP steam boiler at 60 psig on a Maryland jobsite still requires appropriately licensed oversight — typically Grade 4 in a public building or Grade 5 in a qualifying non-public building.
Maryland has had statewide licensing since 2005. County or city business licenses do not substitute for stationary engineer licensure.
Reciprocity, Exams, and Enforcement
Reciprocity FAQ: Maryland does not hold reciprocal agreements that waive the examination based on another state's license. Out-of-state credentials do not authorize regulated operation in Maryland. Candidates must pass the Maryland PSI examination (open-book with Board-approved references) with a score of at least 70% and hold a Maryland license.
Enforcement is complaint-driven. The Board investigates unlicensed practice and disciplinary matters. Document who has charge on each shift, maintain operating logs, and ensure the on-duty license grade matches the largest single regulated object.
Field Checklist Before Every Shift
- Classify each object's pressure, temperature, and HP from nameplates and operating conditions
- Apply the heating exclusion correctly — check both hot water limits
- Identify the largest single regulated object for grade (ignore aggregate sums)
- Confirm Maryland licensure for portable/leased equipment and out-of-state staff
- Verify the engineer on duty holds a grade equal to or higher than required
- Separate operator licensure (Title 6.5) from equipment inspection (Boiler Safety Act)
Common Exam Traps
- Trap: Adding HP of all boilers on a common header to set grade. Correct rule: largest single regulated object only.
- Trap: Assuming all heating boilers are unregulated. Correct rule: exclusion applies only within stated pressure/temperature bands.
- Trap: Believing portable boilers are exempt because they are temporary. Correct rule: regulated thresholds still apply.
- Trap: Assuming an out-of-state license allows immediate operation. Correct rule: no reciprocal exam waiver; Maryland license required.
A facility operates three 90 HP steam boilers at 125 psig on a common header (270 HP total). What governs the minimum license grade?
Which hot water heating boiler is excluded from Maryland stationary engineer licensing?
A leased portable steam boiler rated 45 HP at 60 psig is brought onto a Maryland jobsite. What is true about licensure?
An engineer holds a Grade 2 license from another state. What does Maryland reciprocity guidance require before operating a regulated plant in Maryland?