Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ANSI Z21.40.2-1996 Standard for Gas-Fired Absorption Refrigerators: Scope, Technical Requirements, and Compliance
Comprehensive guide to the safety and performance criteria for gas-fired absorption refrigerators established by ANSI and CGA.
Scope of ANSI Z21.40.2-1996
ANSI Z21.40.2-1996, developed jointly by the American National Standards Institute (ANSI) and the Canadian Gas Association (CGA), specifies the safety, performance, and construction requirements for gas-fired absorption refrigerators. This standard applies to refrigerators that use an absorption cycle fueled by natural gas, propane, or other liquefied petroleum gases. It covers appliances intended for residential, commercial, and recreational vehicle (RV) use, provided they operate at inlet pressures not exceeding ½ psi (3.45 kPa). The standard addresses both single-burner and multi-burner designs, including those with integrated cooling and heating functions, and ensures that such appliances operate safely under normal and abnormal conditions.
The scope excludes electric compression refrigerators and any appliance not primarily designed for refrigeration through absorption. It also does not cover gas-fired absorption heat pumps or air conditioners, which are addressed by separate standards (e.g., ANSI Z21.40.1). By harmonizing U.S. and Canadian requirements, this standard facilitates cross-border certification and reduces duplication of testing.
Technical Requirements
Safety and Combustion
The standard mandates stringent safety provisions, including flame failure devices that automatically shut off gas supply if the burner flame is extinguished. It also requires over-temperature protection (e.g., fusible links or thermostats) to prevent overheating of the absorber generator. All igniters must be spark or glow-coil types that achieve reliable ignition within four seconds. Combustion chamber integrity is validated by a 1.0 psig (6.9 kPa) air pressure test, with no leaks permitted.
Emissions and Efficiency
Maximum allowable carbon monoxide (CO) in undiluted flue gas is 400 ppm air-free, a limit consistent with contemporary gas appliance standards. The standard also requires that the appliance achieve a minimum coefficient of performance (COP) of 0.45 when tested at design conditions (75 °F ambient, 40 °F cold box). Efficiency is measured using the ANSI Z21.40.2 calorimeter method, which accounts for burner input, refrigeration capacity, and auxiliary energy consumption.
Construction and Materials
All wetted parts in the refrigerant circuit must be made of corrosion-resistant materials (e.g., copper, stainless steel, or suitably coated steel). The pressure vessel containing the ammonia-water solution must meet the ASME Boiler and Pressure Vessel Code for a maximum allowable working pressure (MAWP) of 300 psig (2.07 MPa). Joints must be brazed or welded, and threaded connections are prohibited in refrigerant piping to avoid leakage.
| Requirement Type | Specification | Testing Method |
|---|---|---|
| Maximum CO (air-free) | 400 ppm | ANSI Z21.40.2 §4.4 flue gas analysis |
| Minimum COP | 0.45 | ASHRAE 117-1986 calorimeter method |
| Gas supply pressure range | 5–14 inches WC (1.24–3.48 kPa) for natural gas; 10–14 inches WC (2.49–3.48 kPa) for propane | Portable manometer at appliance inlet |
| Burner enclosure air pressure test | No leak at 1.0 psig (6.9 kPa) | Soap bubble test or pressure decay |
| Flame failure response time | < 30 seconds | ANSI Z21.20 flame safeguard test |
Implementation Highlights
Manufacturer Certification
Compliance with ANSI Z21.40.2-1996 is typically demonstrated through third-party testing by a Nationally Recognized Testing Laboratory (NRTL) such as CSA, UL, or Intertek. Manufacturers must submit detailed drawings, bill of materials, and production samples for evaluation. The standard requires that all production units be essentially identical to the tested prototype; any deviation must trigger a re-evaluation.
Tip: When designing the absorption generator, ensure that the solution heat exchanger provides at least 5 °F subcooling at the condenser inlet to maintain COP above the threshold. Early prototype testing with flue gas analysis can identify combustion issues before full-scale certification.
Field Installation and Use
The standard includes installation requirements, such as minimum clearances to combustible surfaces (typically 6 inches from sidewalls and 18 inches above the burner compartment). Appliances must be installed in accordance with the National Fuel Gas Code (NFPA 54) or CSA B149.1. For RV applications, additional vibration testing is required to ensure burner retention during travel.
Warning: Gas-fired absorption refrigerators produce hydrogen gas during operation, which can become explosive if ventilation is inadequate. Ensure proper make‑up air is provided per the manufacturer’s instructions and local codes. Never block the air slots at the bottom of the refrigerator cabinet.
Compliance Notes
Marking and Documentation
Each appliance must bear a permanent nameplate indicating the standard number (ANSI Z21.40.2-1996 or CSA 2.2-1996), the certification mark of the accredited agency, gas type, and input rating. Operation and maintenance manuals must include flue gas CO limits and a warning against operating the appliance when gas odor is detected.
Periodic Re-Assessment
While the standard itself is static, compliance verification may be required at intervals specified by the certification body. Some NRTLs mandate annual follow-up inspections at the manufacturing facility to ensure continued conformity. Changes in materials or suppliers that affect safety must be reported within 30 days.
Compliance Success: Many manufacturers achieve a streamlined certification process by designing their refrigerators to meet the 1996 requirements even when targeting later editions of the standard. Using redundant flame sensors and corrosion-resistant materials often yields zero-defect test results on first submission.
Non‑Compliance Risk: A common failure point is insufficient over‑temperature protection. If the generator temperature exceeds the factory‑set limit (typically 375 °F / 190 °C) for more than 2 minutes, the fusible link must de‑energize the gas valve. Testing with a calibrated thermocouple must confirm this before production approval.
Frequently Asked Questions
Q: Is ANSI Z21.40.2-1996 still active?
A: No, this specific edition has been replaced by later versions (e.g., ANSI Z21.40.2-2012). However, many older installations still operate under the 1996 requirements, and the standard remains a reference for legacy equipment and for jurisdictions that adopt earlier editions by reference.
A: No, this specific edition has been replaced by later versions (e.g., ANSI Z21.40.2-2012). However, many older installations still operate under the 1996 requirements, and the standard remains a reference for legacy equipment and for jurisdictions that adopt earlier editions by reference.
Q: What gas types are covered by the standard?
A: The standard covers natural gas (NG, with a specific gravity of 0.60–0.70) and liquefied petroleum gases (propane and butane). It does not cover biogas or other alternative gases unless they meet the same combustion characteristics defined in the standard’s fuel classification table.
A: The standard covers natural gas (NG, with a specific gravity of 0.60–0.70) and liquefied petroleum gases (propane and butane). It does not cover biogas or other alternative gases unless they meet the same combustion characteristics defined in the standard’s fuel classification table.
Q: Can a gas-fired absorption refrigerator be converted from propane to natural gas?
A: Yes, provided the conversion kit is listed by the appliance manufacturer and the change does not alter the CO emissions beyond 400 ppm. The standard requires that the appliance be retested after conversion to verify compliance. In practice, most NRTLs affix a permanent label indicating which gas type the unit is configured for.
A: Yes, provided the conversion kit is listed by the appliance manufacturer and the change does not alter the CO emissions beyond 400 ppm. The standard requires that the appliance be retested after conversion to verify compliance. In practice, most NRTLs affix a permanent label indicating which gas type the unit is configured for.
© 2026 — Technical article based on ANSI Z21.40.2-1996 and CGA 2.2. For official requirements, refer to the latest published edition.