HVAC codes & standards

The model mechanical code adopted at state or local level in most US jurisdictions. IRC Chapter 14 covers one- and two-family dwellings; IMC covers multifamily over three stories and commercial.

The 2024 IMC adds Group A2L and B2L refrigerant provisions, requires leak-detection alarms where safety-relief discharge is not readily visible to occupants, raises minimum dwelling-unit outside-air requirements, and adds rules for common exhaust ducts in multifamily. The 2024 IFGC (companion fuel-gas code) updates A2L/A2/A3/B1 refrigerant equipment standards.

Governs installation of fuel-gas piping systems, gas appliances, venting, and combustion air. Adopted as state or local law in most US jurisdictions. The 2024 IFGC is the ICC parallel.

NFPA 54 covers everything from the gas meter to the appliance: pipe sizing, materials, joint construction, leak testing, appliance connectors, shutoff valves, venting categories, and combustion-air calculations. Updated every three years. NFPA 58 covers propane (LP-gas) specifically. Pressure testing must use air, nitrogen, CO₂, or an inert gas — never fuel gas, propane, or oxygen.

Safety Standard for Refrigeration Systems. The paired UL 60335-2-40 / CSA C22.2 No. 60335-2-40 is the equipment-listing standard for A2L comfort cooling.

A2L refrigerants (R-32 GWP 675, R-454B GWP 466) are "mildly flammable" and replace R-410A in most new residential and light-commercial HVAC equipment. ASHRAE 15-2022 sets the maximum charge per occupied volume, requires factory-installed refrigerant detection and dissipation for systems over ~3.91 lb A2L, and mandates A2L-rated recovery equipment, manifold gauges, and leak detectors. Sensors trip at 20% of the lower flammability limit and trigger fan dissipation airflow.

62.1 governs ventilation for non-residential buildings; 62.2 covers residential. Adopted as the basis for ventilation requirements in IRC, IECC, Energy Star, LEED, and Passive House.

ASHRAE 62.1-2025 (published late 2025) adds two new requirements: an Economizer Shutdown mode for use "in the event that the outdoor air is more contaminated than typical, for example during a wildfire event," and an Infection Risk Management Mode. ASHRAE 62.2 residential rate: Qtot = 0.03 × Afloor + 7.5 × (Nbr + 1), in CFM. AHJ adoption of 62.1-2025 lags publication — confirm the in-force edition.

Energy standard for buildings except low-rise residential. Adopted by reference in many state energy codes. Defines minimum equipment efficiency, building envelope, duct sealing/leakage, and controls.

For HVAC the most-cited 90.1-2022 provisions are §6.4.4.2 (all ducts sealed; ducts >3 in. w.g. require leakage testing per the SMACNA leakage manual), Tables 6.8.1 (commercial equipment minimum efficiency), and Appendix L (Total System Performance Ratio pathway).

National Electrical Code. Articles 422 (appliances), 424 (fixed electric space-heating), 430 (motors), and 440 (air-conditioning and refrigerating equipment) cover HVAC.

NEC 2023 closed a long-running ambiguity in §440.14: the disconnect must meet §110.26(A) working-clearance dimensions (≥36″ depth, ≥30″ width or width of equipment, ≥6′6″ height). §440.11 requires tool-or-lockable enclosures where the disconnect is accessible to unqualified persons. §210.63 requires a 125V receptacle within 25 ft of HVAC equipment, on the same level, accessible.

Federal certification required for anyone who services, repairs, or disposes of refrigerant-containing equipment. Certifications do not expire. Section 608 covers A2Ls; A2L-specific safety training is additionally recommended.

Type I (small appliances ≤5 lb), Type II (high-pressure systems including residential/commercial AC), Type III (low-pressure chillers), or Universal. The Core test must be proctored to obtain Universal. Connecting a manifold to a sealed residential system, recovering refrigerant before scrapping equipment, and purchasing refrigerant all require certification.

Per EPA, the AIM Act "mandates the phasedown of HFCs by 85 percent from historic baseline levels by 2036." The Technology Transitions Rule imposed a 700-GWP cap on new residential/light-commercial AC and heat-pump equipment.

R-410A new-equipment manufacturing stopped January 1, 2025. The current dominant replacements are R-454B ("Opteon XL41" / "Puron Advance"; GWP 466) for ducted split systems and R-32 (GWP 675) for ductless mini-splits — both A2L. The original January 1, 2026 installation cutoff for pre-2025 R-410A residential/light-commercial equipment has been removed: after the Oct 3, 2025 reconsideration proposal (comment period closed November 21, 2025), EPA published a final rule on May 26, 2026 eliminating the residential/light-commercial install cutoff, so existing R-410A inventory may continue to be installed. State laws (CA, CO, NY, WA, NJ) may still apply, and the 700-GWP cap on new manufacturing remains the law.

Leak detection and repair requirements drop from 50 lb to 15 lb charge threshold on January 1, 2026 (for refrigerants with GWP >53). Annual leak inspection required.

Beginning 2026-01-01, any HFC-containing appliance with ≥15 lb refrigerant charge is subject to leak-rate triggers: 20% for commercial refrigeration, 30% for industrial process, 10% for comfort cooling — leaks above these thresholds must be repaired within 30 days or a retrofit/retirement plan submitted within 120 days. Automatic leak detection systems are required on industrial/commercial refrigeration ≥1,500 lb charge (new systems by 2026-01-01; existing by 2027-01-01). Supermarket / refrigerated-transport / ice-maker servicing must use reclaimed HFCs starting 2029-01-01.

Effective January 1, 2023. Test procedures use 0.5 in. w.g. external static pressure (5× the previous test value), so SEER2 numbers run lower than the legacy SEER scale.

North region (most states above the 35th parallel) allows sell-through based on manufacture date; Southeast and Southwest are install-date based — non-compliant equipment cannot be legally installed after the cutoff. Southwest adds EER2 requirements to protect peak-load grid stress.

Revised PPE rule for construction. Took effect January 13, 2025. PPE must be of safe design and properly fit each employee.

The amendment explicitly closes the "one-size-fits-all" loophole. PPE that does not fit the worker (gloves too large, eye protection that slips, hard hats poorly sized) is no longer compliant even if the item itself is rated correctly. This is now a frequent OSHA citation driver.

Trenches and excavations on construction sites. Protective system required at ≥5 ft (sloping, benching, shoring, or shielding); RPE-designed system required ≥20 ft.

Daily inspection by a competent person, spoils kept ≥2 ft from edge, ladder/ramp egress within 25 ft of workers in trenches ≥4 ft. Trench collapse is the single most common fatal injury in plumbing service-line work.

1910.146 is the General Industry permit-required confined-space rule; 1926 Subpart AA is the Construction-industry equivalent. Atmospheric testing order: O₂ (19.5–23.5%), combustibles (<10% LEL), toxics.

Many plumbing and HVAC service spaces qualify: tanks, vaults, sewer manholes, crawlspaces, large duct/AHU interiors. Permit, attendant, retrieval system, communication, and a written rescue plan are all required for permit-required confined spaces.

Notice of Proposed Rulemaking 89 FR 70698, published August 30, 2024. Informal hearing concluded July 2, 2025; post-hearing comments closed October 30, 2025. No final standard yet.

Until a federal standard is finalized, OSHA enforces heat hazards through the General Duty Clause and the 2022 National Emphasis Program on heat. State standards exist in California (Title 8 §3395), Colorado, Minnesota, Oregon, Washington, and Maryland (proposed). Nevada's heat regulation R131-24AP was adopted October 28, 2024 and approved by the Legislative Commission November 15, 2024, with enforcement beginning April 29, 2025.