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ANSI Z21.13-2017 / CSA 4.9-2017: Gas-Fired Low-Pressure Steam and Hot Water Boilers — Technical Requirements and Compliance
A comprehensive guide to the scope, design criteria, safety provisions, and regulatory adoption of the joint US-Canada boiler standard
Scope of ANSI Z21.13-2017 / CSA 4.9-2017
The joint standard ANSI Z21.13-2017 / CSA 4.9-2017 establishes minimum requirements for the safe operation, performance, and construction of gas-fired low-pressure steam and hot water boilers. It applies to boilers intended for commercial and residential use, with input ratings up to 400,000 Btu/hr (117.2 kW) for steam boilers and 500,000 Btu/hr (146.5 kW) for hot water boilers. The standard covers boilers fueled by natural gas, propane, or manufactured gas, and includes both atmospheric burner and forced-draft designs.
The scope explicitly excludes electric boilers, high-pressure steam boilers, and boilers used exclusively for process heating. Also excluded are cast-iron sectional boilers and certain special-purpose units that may be covered by other standards (e.g., ASME Section IV).
Important: Boilers covered by this standard must operate at a maximum allowable working pressure of 15 psi (103 kPa) for steam and 160 psi (1,103 kPa) for hot water, with operating temperature limited to 250°F (121°C).
Technical Requirements
Materials and Construction
All pressure-containing parts must meet the material specifications referenced in the standard, including minimum thickness requirements for shell and tube sheets. Welding and brazing procedures must comply with ASME Section IX or an equivalent code. The standard also mandates that boilers be equipped with a pressure relief valve or temperature and pressure relief valve as appropriate, sized to relieve at a capacity not less than the burner input.
Safety Control Systems
ANSI Z21.13-2017 requires redundant gas shut-off valves for boilers with inputs above 400,000 Btu/hr. All units must include a flame supervision device (flame rod or thermocouple) that interrupts gas flow within 90 seconds if flame is lost. A manual reset high-limit control is mandatory on steam boilers; hot water boilers require an automatic limiting device. Additionally, boilers must be equipped with a flow switch or mechanical means to prevent firing without adequate water circulation.
Performance and Efficiency
The standard includes thermal efficiency test procedures using the steady-state method. Minimum thermal efficiency for gas-fired boilers under this standard is 80% for hot water units and 75% for steam units. The testing also covers flue gas temperature, CO/CO₂ ratio, and excess air levels. Standby loss and jacket loss are measured to ensure reasonable energy conservation.
Table: Key Technical Parameters
| Parameter | Steam Boiler | Hot Water Boiler |
|---|---|---|
| Maximum Input Rating (Btu/hr) | 400,000 | 500,000 |
| Maximum Working Pressure | 15 psi (103 kPa) | 160 psi (1,103 kPa) |
| Maximum Operating Temperature | 250°F (121°C) | 250°F (121°C) |
| Minimum Thermal Efficiency | 75% | 80% |
| Standby Loss Limit (max %) | 1.5 | 1.0 |
| Flame Failure Response Time | ≤ 90 seconds | |
| Gas Valve Train ( > 400,000 Btu/hr ) | Redundant shut-off with proof of closure | |
Efficiency Tip: While the standard sets minimum efficiency, many modern condensing designs exceed the 80% threshold. Engineers should consider specifying boilers with 90%+ thermal efficiency for long-term energy savings and reduced greenhouse gas emissions.
Implementation and Testing Highlights
Certification Testing
Manufacturers must submit sample boilers to an accredited laboratory for type testing. The test sequence includes:
- Gas input and manifold pressure verification
- Safety control operation under normal, start-up, and shut-down conditions
- Flame stability across varying draft conditions
- Hydrostatic test at 1.5 times the maximum working pressure
- Continuous operation endurance test (typically 100 hours)
Marking and Documentation
Each boiler must bear a permanent nameplate containing manufacturer identification, model number, rated input, fuel type, working pressure, and certification marks. Instructions for installation, operation, and maintenance must be included with each unit. The standard also requires that wiring diagrams and component lists be supplied.
Design Consideration: When designing boiler controls, ensure that the high-limit temperature controller is adjustable and protected from tampering. Some jurisdictions require additional end-switch interlocks for safety.
Critical Safety: Verify that all boilers are equipped with a low-water cutoff device on the steam side (or a flow switch on hot water side) to prevent operation without proper water level. This requirement is strictly enforced during field inspections.
Compliance and Regulatory Notes
Adoption in the United States and Canada
ANSI Z21.13-2017 is recognized by the U.S. Department of Energy as a national safe practice standard. Canadian adoption through CSA generally requires additional province-specific amendments, particularly regarding venting materials and seismic restraints. Many local codes require that boilers bear the CSA/ANSI certification mark to pass installation inspection.
Relationship to Other Standards
This standard complements ASME Section IV for new construction and NFPA 54 (National Fuel Gas Code) for installation. It is not intended to override the ASME boiler pressure-retaining requirements but focuses on gas train, safety controls, and performance. When used in conjunction with CAN/CSA B149.1 (Natural Gas and Propane Installation Code), the boiler installation meets both safety and fuel code requirements.
Updates from Previous Editions
The 2017 edition introduced more stringent requirements for combustion air proving, increased redundancy on larger burners, and improved test methods for standby losses. Manufacturers should review the transition period set by the certifying bodies to ensure continued compliance.
Field Compliance Note: Inspectors frequently cite lack of adequate clearance for combustion air supply and improper relief valve discharge piping. Always consult the latest local fuel gas code in addition to the boiler standard.
Frequently Asked Questions
Q: Does ANSI Z21.13-2017 apply to condensing boilers?
A: Yes, the standard covers both conventional non-condensing and condensing gas-fired boilers. Condensing units must also meet the minimum efficiency requirements and additional material corrosion-resistance measures. The standard does not, however, set specific efficiency tiers; those are covered by separate DOE or Canadian efficiency regulations.
A: Yes, the standard covers both conventional non-condensing and condensing gas-fired boilers. Condensing units must also meet the minimum efficiency requirements and additional material corrosion-resistance measures. The standard does not, however, set specific efficiency tiers; those are covered by separate DOE or Canadian efficiency regulations.
Q: Can a boiler certified to ANSI Z21.13-2017 be used in both the U.S. and Canada?
A: Yes, because it is a joint ANSI/CSA standard, the certification is generally accepted in both countries. Some provinces require additional markings (e.g., TSSA for Ontario), but the core safety and performance requirements are harmonized.
A: Yes, because it is a joint ANSI/CSA standard, the certification is generally accepted in both countries. Some provinces require additional markings (e.g., TSSA for Ontario), but the core safety and performance requirements are harmonized.
Q: What is the maximum input rating covered by this standard?
A: For steam boilers the maximum input rating is 400,000 Btu/hr (117.2 kW). For hot water boilers it is 500,000 Btu/hr (146.5 kW). Boilers with inputs above these ratings may fall under other standards such as ANSI Z21.17 or ASME Section IV.
A: For steam boilers the maximum input rating is 400,000 Btu/hr (117.2 kW). For hot water boilers it is 500,000 Btu/hr (146.5 kW). Boilers with inputs above these ratings may fall under other standards such as ANSI Z21.17 or ASME Section IV.
Q: How often must field-installed safety controls be tested?
A: The standard does not specify maintenance intervals, but it references installation instructions that recommend annual inspection of safety controls, pressure relief valves, and flue gas passages by a qualified service technician. Local codes often require annual testing of low-water cutoffs and relief valves.
A: The standard does not specify maintenance intervals, but it references installation instructions that recommend annual inspection of safety controls, pressure relief valves, and flue gas passages by a qualified service technician. Local codes often require annual testing of low-water cutoffs and relief valves.
— Updated 2026 —