45L Tax Credit Compliance for Kentucky Multifamily Developers: 2026 Field Guide

Practical documentation and field-testing steps for builders claiming §45L in the Ohio Valley.

Why §45L Still Matters After the OBBB Extension

The §45L energy-efficient home credit was extended and modified by the One Big Beautiful Bill, but the core documentation discipline did not change: an eligible contractor must still produce a certified energy analysis and field-verified performance data on every claimed unit. For multifamily developers in Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri, that means HERS Index or ENERGY STAR MFNC verification on every building in the project — not just the model unit.

Two program paths remain dominant for §45L in our region:

• ENERGY STAR Multifamily New Construction (MFNC) certified to the current national revision
• DOE Zero Energy Ready Home (ZERH) with a confirmed HERS Index threshold

Both paths require a certified Rater — RESNET-accredited — to seal the certificate before the contractor files. The deadline pressure is real: projects placed in service after June 30, 2026, fall under revised credit values, and pre-construction eligibility determinations carry forward only when field performance matches the design.

Field Tests HECS Runs for 45L Documentation

For MFNC projects, HECS bundles four field tests into a single mobilization. Each produces a separate deliverable that flows into the RESNET registry and the ENERGY STAR submission.

• Blower door testing at 50 Pa to confirm the building envelope meets the program's ACH50 target (typically 3–5 ACH50 for ENERGY STAR MFNC; the binding value depends on the certified software report)
• Duct leakage testing to the outside, CFM25 per 100 sq ft of conditioned floor area
• Air-handler airflow verification using a flow plate or capture hood, with duct-leakage-to-inside flagged separately
• Thermal imaging of the envelope and duct trunk lines during the blower door depressurization to identify gap locations

For ENERGY STAR MFNC v3.1 and v3.2 projects, the verification checklists require the Rater to confirm HVAC design per ACCA Manual S and Manual D, with Manual J load calcs retained in the project file. HECS retains those documents in the certification packet we hand back to the developer.

Working with HECS

HECS handles blower door testing, duct leakage testing, and HERS Rater certification for multifamily projects in Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a pre-construction scope review: (859) 983-7382 or [email protected]. We staff up to four mobilizations per week in the Cincinnati–Louisville–Lexington corridor.

Code Context: IECC, ASHRAE 90.1, and 90.1-2019 Thresholds

The 2024 IECC residential provisions (R402.4.2 and Table R402.4.1.1) govern air-leakage testing for dwelling units in our region, which falls in climate zones 4A and 5A. The 5 ACH50 ceiling for CZ 4A was established in the 2012/2015 IECC cycle and was largely reaffirmed by the 2024 IECC — not reversed. Buildings pursuing the 2024 IECC must also meet the corresponding duct-leakage target in Table R402.4.2.

Projects that opt into ASHRAE 90.1-2019 follow a different compliance pathway but produce overlapping field data. In our experience, a building that clears the 2024 IECC envelope numbers typically also clears 90.1-2019 §6.5.7 with margin. The two programs diverge most on HVAC efficiency metrics, where 90.1-2019 carries higher minimum equipment efficiencies.

For projects also pursuing NGBS-2023 certification, the air-leakage provisions apply at the dwelling-unit level, but the program adds a separate duct-leakage maximum in the mechanical sections. HECS verifies both at the same visit.

Common Pitfalls on §45L Submissions

Three recurring failures show up in our project files:

1. Duct leakage to inside measured at the air handler exceeds program limits, even when total duct leakage passes. The inside fraction is checked separately.
2. Manual J loads were never sealed by the HVAC contractor. ENERGY STAR MFNC requires sealed design documentation, not a stamped sales sheet.
3. The Rater of record changes mid-project without a registry update, which invalidates the registration file.

The fix is procedural: lock the design and the verifier before insulation, not after drywall.

Frequently Asked Questions

Does the §45L credit require a HERS Index, or is ENERGY STAR MFNC certification sufficient on its own? ENERGY STAR MFNC certification is sufficient for the §45L base credit, provided a RESNET-accredited Rater signs the certification and the building is placed in service within the eligibility window. A separate HERS Index is required only when the contractor pursues the DOE ZERH alternative path.

What field tests does HECS run for a 50-unit garden-style project in Louisville or Lexington? HECS runs blower door, duct leakage (total and to outside), air-handler airflow, and thermal imaging on a sampled set of units per the program sampling protocol. The same mobilization covers NGBS verification where applicable, reducing return trips to the site.

Can a project still claim §45L if the 2024 IECC air-leakage test fails on one unit? A single unit failure does not automatically disqualify the project, but it does require corrective work and a re-test before the certification is sealed. In our experience, builders budget two re-test mobilizations to absorb the typical punch-list failures.

How does HECS coordinate with the HVAC contractor during construction? HECS reviews the ACCA Manual J/S/D design package before rough-in inspection, flags oversized or undersized equipment against the load calc, and returns to the site for the air-handler flow verification at trim-out. That coordination is what produces a clean submission packet at final inspection.

What documentation should the developer retain for an IRS substantiation review? Retain the certified Rater registration, the ENERGY STAR MFNC certificate or DOE ZERH certificate, the field-test report (blower door, duct leakage, airflow), and the sealed energy analysis. HECS provides all four in the final certification packet.

How to Engage HECS

HECS scopes §45L certification, ENERGY STAR MFNC verification, blower door testing, duct leakage testing, and FORTIFIED Home evaluation for multifamily projects across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. Our team serves Louisville KY, Lexington KY, Cincinnati OH, Indianapolis IN, Nashville TN, Evansville IN, and Columbus OH — with two-person mobilizations typically deployable within 10 business days. Call (859) 983-7382 or email [email protected] to start a pre-construction scope review. Service details: hecsusa.com/services/. Project intake form: hecsusa.com/contact/. For 45L-specific scoping in Louisville: hecsusa.com/45l-tax-credit-louisville-ky/.