Delaware
For Delaware, governing body is The Delaware Department of Natural Resources and Environmental Control; statute citation is Delaware Code, Title 7, Chapter 74B, Section 7401B; power boiler inspection interval is annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections; low-pressure boiler inspection interval is biennial external inspections; accepted inspector types is commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies, verified against its source on 2026-08-05.
- State
- Delaware
- Governing body
- The Delaware Department of Natural Resources and Environmental Control
- Statute citation
- Delaware Code, Title 7, Chapter 74B, Section 7401B
- Power boiler inspection interval
- annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections
- Low-pressure boiler inspection interval
- biennial external inspections
- Accepted inspector types
- commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies
- Pressure vessel inspection interval
- biennial or every four years as determined by the inspector per nationalboard.org
- Exemptions
- Boilers or pressure vessels subject to federal inspection and control; pressure vessels used for transport or storage of compressed gases and liquids under US DOT control (including CO2 Dewars); air tanks on vehicles under other state agency authority; air tanks on railroad rights-of-way; unfired pressure vessels not exceeding 5 cu ft/250 psig or 3 cu ft/350 psig or 1-1/2 cu ft/600 psig or 6 inches inside diameter; unfired pressure vessels with operating pressure not exceeding 15 psig; water-containing vessels of 120 gallons or less; water filters or softeners at ambient temperature not exceeding 300 psig; pressure vessels under state fire marshal control; high pressure breathing air cylinders used by emergency response organizations (maintained per manufacturer and NFPA standards); water heaters not exceeding 200,000 BTU/hr (or 58,600 watts), 210°F, 120 gallons; coil-type hot-water boilers without steam space under specified limits; heating boilers and pressure vessels in buildings solely used for residential purposes with not more than six family units per nationalboard.org
What the source says
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
— chardonlabs.com, retrieved 2026-08-05
Sources disagree
More than one authority states this, and they do not state the same thing. Both are reproduced with the source each came from — deciding between them is yours, not ours.
Governing body
chardonlabs.com says governing body is The Delaware Department of Natural Resources and Environmental Control, as of 2026-08-05.
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
nationalboard.org says governing body is Department of Natural Resources and Environmental Control, DNREC, Boiler Safety, as of 2026-08-05.
Power boilers, miniature boilers, and high-pressure, high-temperature water boilers: Annual internal inspection; Annual external inspection while under pressure. The external (inservice) inspection should be done within six months of the internal inspection. Low-pressure steam heating boilers, hot-water heating boilers, and hot-water supply boilers: biennial external inspection. Unless exempt from Field Inspection. Pressure vessels: biennial or every four years as determined by the inspector. Unless exempt from Field Inspection.
https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select
Statute citation
chardonlabs.com says statute citation is Delaware Code, Title 7, Chapter 74B, Section 7401B, as of 2026-08-05.
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
nationalboard.org says statute citation is Delaware Code, Title 7 Conservation Chapter 74B. Department of Natural Resources and Environmental Control, Section 7401B Boiler Safety Program., as of 2026-08-05.
Power boilers, miniature boilers, and high-pressure, high-temperature water boilers: Annual internal inspection; Annual external inspection while under pressure. The external (inservice) inspection should be done within six months of the internal inspection. Low-pressure steam heating boilers, hot-water heating boilers, and hot-water supply boilers: biennial external inspection. Unless exempt from Field Inspection. Pressure vessels: biennial or every four years as determined by the inspector. Unless exempt from Field Inspection.
https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select
Power boiler inspection interval
chardonlabs.com says power boiler inspection interval is annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections, as of 2026-08-05.
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
nationalboard.org says power boiler inspection interval is Annual internal inspection; Annual external inspection while under pressure (external inspection should be done within six months of the internal inspection), as of 2026-08-05.
Power boilers, miniature boilers, and high-pressure, high-temperature water boilers: Annual internal inspection; Annual external inspection while under pressure. The external (inservice) inspection should be done within six months of the internal inspection. Low-pressure steam heating boilers, hot-water heating boilers, and hot-water supply boilers: biennial external inspection. Unless exempt from Field Inspection. Pressure vessels: biennial or every four years as determined by the inspector. Unless exempt from Field Inspection.
https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select
Low-pressure boiler inspection interval
chardonlabs.com says low-pressure boiler inspection interval is biennial external inspections, as of 2026-08-05.
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
nationalboard.org says low-pressure boiler inspection interval is biennial external inspection, as of 2026-08-05.
Power boilers, miniature boilers, and high-pressure, high-temperature water boilers: Annual internal inspection; Annual external inspection while under pressure. The external (inservice) inspection should be done within six months of the internal inspection. Low-pressure steam heating boilers, hot-water heating boilers, and hot-water supply boilers: biennial external inspection. Unless exempt from Field Inspection. Pressure vessels: biennial or every four years as determined by the inspector. Unless exempt from Field Inspection.
https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select
Accepted inspector types
chardonlabs.com says accepted inspector types is commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies, as of 2026-08-05.
Governing body: The Delaware Department of Natural Resources and Environmental Control administers the Boiler Safety Program under Delaware Code, Title 7, Chapter 74B, Section 7401B. Authorized inspector types: Delaware accepts commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies. Inspection frequency: High-pressure boilers require annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections. Low-pressure boilers require biennial external inspections.
https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
nationalboard.org says accepted inspector types is Insurance company inspectors or Non-traditional Inspection Agency accredited by National Board-369 and approved by The State of Delaware, commissioned by the program (accepted in lieu of program inspector), as of 2026-08-05.
Power boilers, miniature boilers, and high-pressure, high-temperature water boilers: Annual internal inspection; Annual external inspection while under pressure. The external (inservice) inspection should be done within six months of the internal inspection. Low-pressure steam heating boilers, hot-water heating boilers, and hot-water supply boilers: biennial external inspection. Unless exempt from Field Inspection. Pressure vessels: biennial or every four years as determined by the inspector. Unless exempt from Field Inspection.
https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select
Sources
- chardonlabs.comhttps://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/
- nationalboard.orghttps://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select