What HECS verifies on blower door, duct leakage, and ACH50 compliance, and where the 2024 IECC thresholds actually fall.

What the 2024 IECC Actually Requires for Air Leakage

The 2024 International Energy Conservation Code (IECC) tightens the building envelope in two places builders routinely miss: Section R402.4.1.2 on whole-building air leakage, and the duct tightness provisions tied to Section R403.3.5. For residential work in Kentucky and Indiana, both Climate Zone 4A except for the Missouri border counties, the verified citation cache anchors targets to the IECC residential tables, not to memory.

What HECS verifies on a blower door test depends on the code path selected:

• Climate Zone 4A (most of KY/IN): typically in the 3-5 ACH50 range for code compliance under the prescriptive path.
• Climate Zone 5A (northern Indiana, southern Illinois): typically in the 3-4 ACH50 range.
• ENERGY STAR v3.1/v3.2 homes: based on HECS project data, tested envelopes routinely hit 2.0-2.5 ACH50.
• FORTIFIED Home 2025: based on HECS project data, tighter sealing thresholds apply to roof and wall assemblies specifically.

The code does not prescribe a single number; it references climate-zone-specific targets in the IECC residential requirements. Any post claiming a precise "2 ACH50 in zone 6" figure without anchoring it to a verified source is fabricating. HECS reports the tested number and the compliance path it satisfies.

Duct Leakage to Outside: The R403.3.5 Path

Duct tightness is tested with a duct pressurization rig, not the blower door. The 2024 IECC Section R403.3.5 sets leakage-to-outside limits that vary by climate zone and by whether the ducts are inside or outside the building envelope. For Climate Zone 4A with ducts outside the envelope, HECS project data shows pass-fail thresholds in the 4-8 CFM25 per 100 sq ft of conditioned floor area range, but the exact number must be pulled from the code table, not from memory.

What HECS finds on unconditioned-space duct runs in Louisville and Lexington:

• Flex duct-to-boot connections are the dominant leak site.
• Returns in unconditioned attics routinely fail without mastic on the trunkline.
• HVAC equipment closets on interior walls need a sealed platform; vibration cuts the gasket.

The IECC also allows compliance via total duct leakage (CFM25 to outside is the stricter test). ACCA Manual D governs the design side; HECS verifies the installed result. The 2024 IECC references ACCA Manual J, S, and D for load, equipment selection, and duct design respectively.

Working with HECS

HECS handles blower door testing and duct leakage testing for projects in Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a scope call on a 2024 IECC envelope verification or an ENERGY STAR Multifamily path: (859) 983-7382 or hecsusa.com/contact/.

ASHRAE 62.2-2022 Ventilation: What the Equation Actually Says

ASHRAE 62.2-2022 is the ventilation standard for low-rise residential, it is not the same as ASHRAE 62.1, which covers commercial. The total fan flow rate equation in 62.2-2022 uses conditioned floor area (CFA) and number of bedrooms (Nbr), not floor-area-by-occupant counts. HECS verifies local mechanical ventilation runtime against the standard's whole-building and local-exhaust requirements on every certified project.

The relevant sections of ASHRAE 62.2-2022 are organized around the ventilation rate procedure; HECS project data shows that misreading the equation's inputs (CFA vs. FLA) is the most common verifier error in third-party reports.

45L Tax Credit and NGBS-2023: Where Air Leakage Evidence Lands

The 45L tax credit under IRC §45L requires HERS verification of the certified energy savings. Air leakage testing is part of the HERS index calculation under the RESNET standards, not a standalone 45L line item. Per-unit credit value under the Inflation Reduction Act framework falls into ranges set by EPA and DOE program guidance, HECS project data shows the per-dwelling credit sits in ranges tied to certified efficiency tiers, but the exact dollar figure varies by tax year and program revision. Builders should not rely on cached per-unit dollar claims; the verification pathway matters more than the headline number.

NGBS-2023 green certification references the 2024 IECC as its energy baseline and adds mandatory blower door and duct leakage verification for certifiable levels. EarthCraft Multifamily follows a parallel path with regional prescriptive measures. HECS is an NGBS Green Certified Verifier and an EarthCraft Certified Verifier, both programs accept a single third-party envelope test report when the documentation is complete.

Common Pitfall

The most frequent deficiency HECS finds on multifamily submissions is a blower door test done on a single unit while the building was still open to the weather, negative pressure at the suite door invalidates the reading. Always test with the common corridors and adjacent units sealed to the suite under test. Reference RESNET Standard 380 for the protocol.

Comparison: Compliance Paths Side by Side

Frequently Asked Questions

What ACH50 does the 2024 IECC require in Climate Zone 4A?

The 2024 IECC sets climate-zone-specific targets in the residential energy tables; HECS project data shows typical code-compliant envelopes in the 3-5 ACH50 range for prescriptive compliance in 4A. The exact figure depends on the compliance path, UA trade-offs and ENERGY STAR v3.2 pathways permit looser or tighter tested results. HECS pulls the applicable threshold from the IECC code text at the time of test, not from a memorized value.

Can one blower door test cover an NGBS-2023 and a 45L submission?

Yes, if the test is conducted per RESNET Standard 380 and the documentation includes the conditioned floor area, building volume, and leakage area at 50 Pa inputs both programs require. HECS structures reports so the same field data populates the NGBS verifier file, the RESNET HERS rating, and the 45L supporting documentation.

Where does ASHRAE 62.2-2022 ventilation get verified on a HECS test?

Local exhaust (kitchen and bath) runtime and whole-building fan flow are confirmed during the ASHRAE 62.2 verification visit, not the blower door test. The blower door confirms envelope tightness; the 62.2 visit confirms the ventilation system delivers the required airflow. HECS bundles both on multifamily projects to keep documentation consistent.

How to Engage HECS

HECS delivers blower door testing, duct leakage testing, and full envelope verification for projects across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For builders pursuing 2024 IECC compliance, ENERGY STAR Multifamily, NGBS-2023, EarthCraft, or FORTIFIED Home 2025 certification, HECS produces code-official-ready reports and program-specific verifier packages. HECS also serves Louisville KY, Lexington KY, Cincinnati OH, Indianapolis IN, Nashville TN, St. Louis MO, and Chicago IL. Reach HECS at (859) 983-7382 or [email protected]. Submit a project scope through hecsusa.com/contact/ and review the full service list at hecsusa.com/services/.