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ANSI Z21.40.2a-1997 (R2017): Safety and Performance Criteria for Gas-Fired Absorption Air Conditioning Appliances
A Technical Overview of the Joint ANSI/CGA Standard for Space Cooling Equipment
Scope of the Standard
Applicability and Definitions
ANSI Z21.40.2a-1997 (R2017) – Gas-Fired Absorption Summer Air Conditioning Appliances – establishes minimum safety and performance requirements for factory‑built, gas‑fired absorption cooling equipment. Developed jointly with the Canadian Gas Association (CGA, now part of CSA Group), this binational standard applies to appliances used in residential, commercial, and industrial space‑conditioning applications that utilize an absorption cycle to produce chilled water or conditioned air. The addendum ‘a’ included editorial clarifications and updated references to companion standards such as ANSI Z21.40.1 (for winter heating) and ANSI Z21.40.3 (for heat pump packages).
Revisions in Addendum a
Published in 1997 and reaffirmed in 2017 without substantive changes, the addendum refined the scope to explicitly exclude appliances that incorporate vapor‑compression cycles for supplementary cooling. It also aligned test pressure categories with the latest editions of NFPA 54/ANSI Z223.1 (National Fuel Gas Code) and CAN/CSA B149.1 (Natural Gas and Propane Installation Code).
Technical Requirements
Design and Construction
All appliances covered by ANSI Z21.40.2a must be designed to withstand maximum operating gas supply pressures of ½ psig (3.5 kPa) for natural gas and ½ psig (3.5 kPa) for propane, unless otherwise specified by the manufacturer. The standard mandates that the generator, absorber, condenser, and evaporator satisfy proof‑pressure tests at 2.0 times the maximum allowable working pressure, with no permanent deformation or leakage. Controls must include automatic gas shutoff valves that close within 10 seconds of a flame failure. Additionally, electrical ignition systems must meet the requirements of ANSI Z21.20 (automatic gas ignition systems).
Performance Criteria
The standard specifies minimum cooling capacities and coefficient of performance (COP) at rated conditions (indoor temperature 80°F / 26.7°C dry bulb, outdoor temperature 95°F / 35°C dry bulb). Table 1 summarizes the key performance requirements for two common appliance classes.
| Parameter | Class A (Residential) | Class B (Commercial) |
|---|---|---|
| Rated cooling capacity (Btu/h) | ≥ 36,000 | ≥ 120,000 |
| Minimum COP at full load | 0.50 | 0.55 |
| Maximum sound level (dBA at 3 ft) | 55 | 65 |
| Maximum gas consumption (Btu/h per ton) | 24,000 | 22,000 |
| Electrical standby power (W) | ≤ 10 | ≤ 25 |
Tip: When designing for higher‑efficiency absorption chillers, manufacturers often exceed the minimum COP of 0.50. Modern systems using double‑effect cycles can achieve COP values above 1.0, but they must still comply with the basic safety and test criteria of this standard.
Implementation and Testing Highlights
Test Conditions
Testing must be conducted at a gas supply pressure of 7 inches water column (1.74 kPa) for natural gas and 11 inches water column (2.74 kPa) for propane. All cooling capacity tests use a recirculating chilled‑water loop with a 12°F (6.7°C) temperature differential across the evaporator. The standard also requires a simulated wind test (up to 25 mph / 11 m/s) for outdoor units to verify stable combustion and adequate draft. Any flue gas spillage during this test constitutes a failure.
Certification Marks
Success: Appliances that successfully meet the requirements of ANSI Z21.40.2a are permitted to bear the ANSI/CGA (now CSA) certification mark. This mark is recognized by most North American code authorities and qualifies the product for installation under the International Mechanical Code (IMC) and the National Fuel Gas Code.
The test regimen comprises three main phases:
- Leakage and Proof‑Pressure Tests – Each refrigerant and water circuit must hold pressure at 1.5 times the design pressure for at least 5 minutes without a pressure drop exceeding 1%.
- Combustion and Venting Tests – Carbon monoxide (CO) in undiluted flue products must not exceed 0.04% by volume for natural gas and 0.05% for propane. Spillage limits follow the requirements of ANSI Z21.40.2a.
- Performance and Endurance Tests – A 200‑hour cyclic endurance test subjects the appliance to normal and extreme operating conditions, including interrupted gas supply and voltage variation (±10%).
Compliance and Regulatory Notes
U.S. and Canadian Adoption
ANSI Z21.40.2a-1997 (R2017) is referenced by the U.S. Department of Energy (DOE) for federal energy conservation standards and is accepted by Canadian provincial authorities through the CSA B149 series. Manufacturers selling absorption cooling equipment in North America should use the current edition of the standard in conjunction with the relevant installation codes.
Warning: Some local jurisdictions require additional compliance with UL 2075 (gas and vapor detectors) or ASHRAE Standard 15 (refrigeration system safety). Always verify local amendments.
Periodic Reaffirmation and Future Revisions
The standard’s reaffirmation in 2017 confirmed that no technical changes were necessary. However, with the increasing interest in natural‑gas‑fired heat pumps and triple‑effect absorption cycles, a future revision may introduce higher efficiency tiers and updated test conditions to reflect modern design practices. Users of this standard are advised to monitor the CSA Group’s annual updates for any proposals to modify ANSI Z21.40.2a.
Danger: Never attempt to field‑convert a gas‑fired absorption air conditioner to a different fuel type without a certified conversion kit. The standard requires factory‑engineered fuel‑specific components; unauthorized modifications can lead to carbon monoxide poisoning, fire, or explosion.
Frequently Asked Questions
Q: Does ANSI Z21.40.2a cover both air‑cooled and water‑cooled absorption chillers?
A: Yes. The standard applies to appliances that use either air‑ or water‑cooled condensers and absorbers, provided they meet the applicable safety and performance criteria. The test conditions, however, are written around air‑cooled outdoor applications; water‑cooled models may require additional testing per the manufacturer’s specifications.
A: Yes. The standard applies to appliances that use either air‑ or water‑cooled condensers and absorbers, provided they meet the applicable safety and performance criteria. The test conditions, however, are written around air‑cooled outdoor applications; water‑cooled models may require additional testing per the manufacturer’s specifications.
Q: Can an appliance that is certified to the 1997 version still be installed today?
A: Because the 2017 reaffirmation introduced no technical changes, appliances manufactured in accordance with the original 1997 addendum remain compliant as long as they carry a valid certification mark. Always check local code requirements, as some authorities may demand a newer edition of the standard.
A: Because the 2017 reaffirmation introduced no technical changes, appliances manufactured in accordance with the original 1997 addendum remain compliant as long as they carry a valid certification mark. Always check local code requirements, as some authorities may demand a newer edition of the standard.
Q: Is there a conflict between ANSI Z21.40.2a and the AHRI 560/570 rating standards?
A: No. ANSI Z21.40.2a focuses on safety and construction, while AHRI 560/570 provide standardized rating methods for capacity and efficiency. Manufacturers must meet both sets of criteria for DOE certification and ENERGY STAR qualification. The table in this article highlights only the minimum performance values required by the ANSI/CGA standard.
A: No. ANSI Z21.40.2a focuses on safety and construction, while AHRI 560/570 provide standardized rating methods for capacity and efficiency. Manufacturers must meet both sets of criteria for DOE certification and ENERGY STAR qualification. The table in this article highlights only the minimum performance values required by the ANSI/CGA standard.
Last updated: 2026