# Delaware — US boiler and pressure vessel inspection requirements by state 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 _(verified: appears in the quote below)_ - **Governing body:** The Delaware Department of Natural Resources and Environmental Control _(verified: appears in the quote below)_ - **Statute citation:** Delaware Code, Title 7, Chapter 74B, Section 7401B _(verified: appears in the quote below)_ - **Power boiler inspection interval:** annual internal and external inspections, with external inspections conducted under pressure within six months of internal inspections _(verified: appears in the quote below)_ - **Low-pressure boiler inspection interval:** biennial external inspections _(verified: appears in the quote below)_ - **Accepted inspector types:** commissioned inspectors holding a National Board Inservice Inspector Commission (IS), commissioned insurance company inspectors, and National Board-369 accredited inspection agencies _(verified: appears in the quote below)_ - **Pressure vessel inspection interval:** biennial or every four years as determined by the inspector _(per nationalboard.org, not stated by the source above)_ - **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, not stated by the source above)_ ## 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. ## 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. ### 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: 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. Source: https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select ## Source - https://www.chardonlabs.com/resources/commercial-boiler-inspection-regulations-by-state/ - https://www.nationalboard.org/PrintAllSynopsis.aspx?Jurisdiction=Select Last verified: 2026-08-05. Review by: 2027-08-05. Part of [US boiler and pressure vessel inspection requirements by state](https://referencesource.org/boiler-inspection-requirements-by-state/).