Residential split-system and air-source heat pump commissioning under the new low-GWP rules.

The Field Problem: Mildly Flammable Refrigerants Are Now the Default

Residential contractors in Louisville and across Kentucky are commissioning R-454B and R-32 systems by default for new construction and most replacements. These A2L refrigerants are mildly flammable, and that single chemistry change ripples through every functional test, leak check, and combustion-safety verification HECS performs on a single-family or low-rise multifamily project.

The field issues are not theoretical. Based on HECS project data, the most common failures on A2L commissioning are charge weight miscalculation, installed-where-the-manufacturer-didn't-list-it violations, and inadequate combustion air documentation on gas furnaces paired with A2L coil boxes in closets. Each one of those creates a reject on the third-party certification path, delaying certificate of occupancy.

The Code Stack: What's Actually Changing

The regulatory floor is layered. EPA's AIM Act framework phases R-410A out of new residential HVAC equipment in favor of A2L alternatives, with the bulk of residential equipment transitions already in effect through 2025 and continuing through 2026 production runs. Louisville contractors are seeing R-454B as the dominant replacement for R-410A in unitary splits and heat pumps; R-32 shows up primarily in ductless mini-splits from certain manufacturers.

Above the EPA floor, builder-driven programs are unchanged in scope but tightened in proof. A2L commissioning must be documented under 2024 IECC R403.3.5 for duct sealing, ASHRAE 62.2-2022 §4.1 whole-building ventilation rates, and NGBS-2023 verifier credentials per §702.1.1.1, the refrigerant change does not relax any of those requirements.

For multifamily work qualifying for the federal credit, the timeline anchor is harder than the chemistry: the 45L credit for builders of energy-efficient homes sunsets for homes acquired after June 30, 2026. A2L commissioning is only one of a dozen 45L items that must close by that deadline.

What HECS Verifies on an A2L Commissioning Walk

HECS treats A2L as a charge-test-and-document scope, not a refrigerant swap. The deliverable HECS produces for a Louisville-area split system or heat pump typically includes the following field items, itemized for the builder's rater file:

• Refrigerant charge verification per manufacturer procedure, with subcooling or superheat recorded against the manufacturer's A2L charging chart.
• Leak check at the nameplate test pressure appropriate to the refrigerant, with the test medium and duration documented.
• Installed-location check against the manufacturer's listed component clearances, with photo evidence for closet and attic installations.
• Line-set isolation and joint accessibility verification, since A2L service port requirements diverge from legacy R-410A practice in some equipment families.
• Combustion air and vent clearance documentation where a gas furnace shares the air handler cabinet or closet.
• Duct leakage to outside per the governing code path. Under 2024 IECC R403.3.5, total leakage must not exceed 4 CFM25 per 100 ft² of conditioned floor area, HECS reports this against conditioned floor area, never nominal tonnage.
• Whole-building ventilation rate verification against ASHRAE 62.2-2022 §4.1, including the MERV filtration credit path where applicable.
• Refrigerant leak-detection circuitry operational check where the equipment ships with the required sensor package for the installed location class.

HECS delivers these as a single commissioning report formatted to be dropped directly into the rater file for ENERGY STAR, NGBS Green, or 45L certification.

Working with HECS

HECS handles HVAC Testing & Balancing for A2L-equipped projects throughout Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a scope call on a Louisville single-family or Lexington-area multifamily A2L commissioning: (859) 983-7382 or hecsusa.com/contact/.

Comparison of Governing Thresholds That Apply to A2L Projects

Common Pitfall: A2L in a Closet Without a Leak Sensor

Based on HECS field experience, the most frequent A2L reject on Louisville-area jobs is a furnace and coil in a small interior closet where the manufacturer's installation instructions require a refrigerant leak-detection device and the installer's standard practice from the R-410A era did not. The sensor package was either not ordered, not wired to the indoor unit control board, or installed without the required annunciation path. The fix is rarely hard, it is paperwork and re-wire, but it is consistently missed until HECS flags it on the commissioning walk.

A close second is refrigerant overcharge. A2L thermophysical properties differ from R-410A; subcooling targets that landed a contractor within tolerance last year now leave the system two ounces high. HECS verifies the manufacturer charging chart on every commissioning, not the contractor's recall of last year's number.

Frequently Asked Questions

Does R-454B require a different blower door test than R-410A?

No. The refrigerant chemistry does not change the building envelope test. Per 2024 IECC R402.4.1.2, blower door verification at 3.0 ACH50 (Kentucky CZ 4A) is unchanged.

What credential does HECS carry for testing and balancing?

HECS field staff hold the NCI Commercial Air Balancer credential, among other NCI certifications, and operate as a third-party verifier, not an installer, on every project.

Where does A2L commissioning fit into a 45L certification file?

A2L commissioning documentation is one element within the broader certification package required for the §45L credit, which expires for qualifying homes acquired after June 30, 2026.

How to Engage HECS

HECS commissions A2L-equipped residential HVAC for Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For Louisville and Lexington projects, see the HECS services page and the HECS Louisville service area page. Field staff also serve Cincinnati, Indianapolis, Nashville, Evansville, and St. Louis. Reach HECS at (859) 983-7382 or [email protected] to schedule a commissioning walk. A2L projects typically need two weeks lead time ahead of the certificate of occupancy date, not because the field work is slow, but because the rater file must be clean before final inspection.