Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ANSI Z21.94-2006 / CSA 6.31-2006 (2016): Gas-Fired Construction Heaters – Technical Requirements and Compliance
Comprehensive Overview of the Dual American and Canadian Standard for Safety and Performance of Portable Construction Heaters
The dual standard ANSI Z21.94-2006 / CSA 6.31-2006 (2016) establishes uniform safety, performance, and marking requirements for newly produced gas-fired construction heaters. Jointly developed by the American National Standards Institute (ANSI) and the Canadian Standards Association (CSA), the standard covers portable, direct-fired, indirect-fired, and radiant heaters that operate on natural gas, manufactured gas, or LP-gas (propane). Reaffirmed in 2016, it remains a critical reference for manufacturers, certification bodies, and regulatory agencies in North America.
Scope and Application
This standard applies to portable construction heaters intended for temporary use at building and construction sites. These appliances are typically employed for drying materials, curing concrete, or providing temporary heat in open or semi-enclosed areas. The standard specifically excludes permanently installed heating equipment, furnaces, and heaters rated above 400,000 Btu/h (117 kW). It covers three main heater types:
- Direct-fired heaters – combustion products vent directly into the heated space.
- Indirect-fired heaters – combustion products are exhausted outdoors via a flue system.
- Radiant heaters – heat is emitted primarily by infrared radiation from a burner or element.
The standard addresses all essential aspects including construction, fuel system integrity, combustion performance, safety shutoff features, and labeling. It is harmonized between the United States and Canada, allowing manufacturers to obtain a single certification mark (e.g., CSA) that satisfies both countries’ requirements.
Important: Heaters equipped with an oxygen depletion sensor (ODS) or tip-over shutoff must meet additional performance criteria defined in Sections 4 and 5 of the standard. Always verify the heater’s design for the intended environment.
Technical Requirements
The standard prescribes rigorous performance tests and construction specifications. Key technical areas include combustion stability, gas pressure regulation, tipping stability, marking durability, and electrical safety for any integral fans or controls. Every heater must be subjected to a series of laboratory tests that simulate extreme conditions encountered on construction sites.
| Test Requirement | Description | Acceptance Criteria |
|---|---|---|
| Combustion Performance | Operate at rated input with high and low gas pressures; observe flame characteristics. | No flame lift-off, flashback, or rollout. CO/CO₂ ratio below 0.04. |
| Tipping Stability | Place the heater on a tilting platform; tilt up to 15° in any direction. | Heater must not tip over; if tip-over occurs, safety shutoff must activate within 30 seconds. |
| Gas System Pressure Tightness | Pressurize the gas train to 1.5 times the maximum inlet pressure. | No measurable leakage using a soap solution or pressure decay method. |
| Marking Durability | Apply water, oil, and abrasion to rating plates and warning labels. | Markings must remain legible and attached after testing. |
| Oxygen Depletion Shutoff (if applicable) | Enclose heater in a test chamber and reduce O₂ to 18% (simulated). | Heater must shut down within 5 minutes of reaching 18% O₂. |
Additional requirements cover hose and regulator specifications (Section 6), electrical controls (Section 7 for fan-assisted models), and clearances to combustible materials (Section 8). The standard also mandates that all manual gas valves be of the “positive shut-off” type to prevent inadvertent gas flow.
Hazard: Failure to meet the oxygen depletion shutoff requirement can lead to carbon monoxide poisoning in enclosed spaces. Direct-fired heaters must never be used in occupied, unventilated areas unless they are certified to ANSI Z21.94 with a functioning ODS system.
Implementation and Certification Highlights
Manufacturers seeking to market gas-fired construction heaters in the U.S. and Canada must obtain product certification from an accredited third-party agency such as CSA Group, UL, or Intertek. The certification process involves:
- Submission of construction drawings and component lists.
- Type testing of representative samples in a qualified laboratory.
- Factory inspection to verify production consistency.
- Authorization to apply the appropriate listing mark (e.g., CSA or ANSI-certified label).
Because the standard is dual‑flagged as both an American National Standard and a Canadian standard, a single certification suffices for both markets. This harmonization reduces duplication of testing and facilitates trade.
Tip: When designing a heater for dual-market certification, ensure that the rating plate includes both the ANSI and CSA designations (e.g., “ANSI Z21.94-2006 / CSA 6.31-2006 (2016)”) along with the fuel type, input rating, and clear warning statements. Use of generic warning text may require revision for Canadian bilingual (English/French) requirements.
The 2016 reaffirmation did not introduce technical changes but confirmed that the 2006 edition continues to meet current safety expectations. Nevertheless, manufacturers should stay aware of any addenda released after 2016 that might affect ongoing compliance.
Compliance Benefit: Products certified to the latest edition of ANSI Z21.94/CSA 6.31 demonstrate a strong commitment to worker safety and help reduce liability risks. Many insurance providers and construction contractors require such certification for job‑site equipment.
Compliance and Maintenance
To maintain certification, manufacturers must ensure that all production units consistently match the tested construction. The standard requires:
- Annual factory audits by the certification agency.
- Adherence to the “Report” (the detailed test record) for any changes in materials or components.
- Proper record keeping of production and test results for at least ten years.
It is the responsibility of the manufacturer to notify the certifier of any design changes that could affect compliance. Unauthorized modifications void the certification and expose both the manufacturer and user to serious hazards. Additionally, users and rental companies should follow the manufacturer’s instructions for pre‑operation checks, storage, and maintenance of these appliances.
The standard is periodically reviewed by the Z21/CSA 6.31 Technical Committee, which includes representatives from industry, regulators, and consumers. As combustion technology and fuel compositions evolve, future revisions may incorporate new requirements such as low‑NOx emission limits or enhanced electrical safety.
Frequently Asked Questions
Q: What is the current edition of ANSI Z21.94?
A: The current edition is ANSI Z21.94-2006 / CSA 6.31-2006, reaffirmed in 2016. As of 2026, it remains the prevailing version unless superseded. Always check with a certification body for updates.
A: The current edition is ANSI Z21.94-2006 / CSA 6.31-2006, reaffirmed in 2016. As of 2026, it remains the prevailing version unless superseded. Always check with a certification body for updates.
Q: Does the standard cover electric heaters or heaters that burn kerosene?
A: No. This standard only applies to gas-fired heaters using natural gas, manufactured gas, or LP-gas. Kerosene and electric construction heaters fall under different standards (e.g., ANSI/UL 1278, ASTM F2794).
A: No. This standard only applies to gas-fired heaters using natural gas, manufactured gas, or LP-gas. Kerosene and electric construction heaters fall under different standards (e.g., ANSI/UL 1278, ASTM F2794).
Q: Can I sell a heater built to the 2006 edition after the 2016 reaffirmation?
A: Yes. The reaffirmation does not change technical requirements, so heaters originally certified to the 2006 edition remain compliant. However, always confirm with your certification agency whether any addenda have been issued.
A: Yes. The reaffirmation does not change technical requirements, so heaters originally certified to the 2006 edition remain compliant. However, always confirm with your certification agency whether any addenda have been issued.
Q: What is the difference between “direct-fired” and “indirect-fired” under this standard?
A: Direct-fired heaters release all combustion products into the work area; they require an ODS and clear warnings about ventilation. Indirect-fired heaters use a flue to exhaust gases outdoors, allowing safer operation in enclosed spaces.
A: Direct-fired heaters release all combustion products into the work area; they require an ODS and clear warnings about ventilation. Indirect-fired heaters use a flue to exhaust gases outdoors, allowing safer operation in enclosed spaces.
This article is provided for informational purposes and does not replace the full text of ANSI Z21.94-2006 / CSA 6.31-2006 (2016). Manufacturers and safety professionals should consult the official standard for complete requirements. © 2026 Technical Standards Publishing.