Residential duct leakage testing — commonly called a duct blaster test — measures how much conditioned air your duct system is losing to unconditioned spaces like attics, crawlspaces, and garages before it ever reaches the rooms it was meant to heat or cool. dL Flow Tech performs duct leakage testing throughout the Hudson Valley and NYC metro for new construction energy code compliance, HERS ratings, and diagnostic testing on existing homes. We use calibrated RetroTec equipment and produce the documentation your HERS rater, building department, or energy program requires.
Schedule duct leakage testing: Call (845) 265-2828 or request a quote. Combined blower door and duct blaster tests available in one visit.
What is a duct blaster test?
A duct blaster is a calibrated fan connected to the duct system — typically at the air handler or a return grille — that pressurizes the duct system to a standard 25-Pascal test pressure. The airflow required to maintain that pressure is a direct measure of how much air is escaping through duct leaks: joints, connections, plenums, boots, and any other unsealed opening in the duct assembly.
The duct blaster measures:
- CFM25,total — total duct leakage at 25 Pascals, including leakage to both conditioned and unconditioned spaces.
- CFM25,out (Qn,out) — leakage to outside, meaning leakage specifically to unconditioned spaces (attic, crawlspace, garage, exterior). This is the energy-penalty metric the energy code limits.
Qn,out is measured by testing the duct system while also using the blower door to pressurize the house interior, which allows the calculation to isolate only the leaks that go to outside. This combined test is more informative than total duct leakage alone and is required when demonstrating code compliance using the leakage-to-outside metric.
New York State energy code — duct leakage requirements
The New York State Energy Conservation Construction Code (ECCC), based on the IECC, sets mandatory duct leakage limits for new residential construction:
| Compliance Path | Leakage Limit | Basis |
|---|---|---|
| Leakage to outside | ≤ 4 CFM25 per 100 sq ft CFA | Preferred — energy penalty leakage only |
| Total duct leakage | ≤ 12 CFM25 per 100 sq ft CFA | Alternative — harder to achieve |
CFA = conditioned floor area. Testing must be performed by a qualified third party. We produce the documentation the building department needs for certificate-of-occupancy signoff.
HERS ratings and duct leakage
HERS ratings (Home Energy Rating System) incorporate duct leakage directly into the energy score calculation. A duct system leaking 15% of conditioned air to outside contributes substantially to the HERS index — and reducing that to code-compliant levels can improve the HERS score significantly. For builders seeking Energy Star certification or meeting green building standards, certified duct leakage testing by a HERS rater or third-party tester is required.
Energy impact of duct leakage
Duct leakage to outside is one of the most significant and often overlooked sources of energy waste in residential HVAC systems. Conditioned air — air you paid to heat in winter or cool in summer — leaks out of the duct system before it reaches the living space. Simultaneously, unconditioned air from the attic or crawlspace is drawn into the return side of the duct system. The combined effect:
- Heating and cooling loads increase because the HVAC system is conditioning exterior air rather than recirculating interior air.
- Rooms at the end of the duct run don't receive their design airflow — comfort problems result.
- Attic or crawlspace dust and contaminants can be drawn into the duct system and distributed to living spaces.
- Pressure imbalances from leaky ducts can cause rooms to go positive or negative, driving infiltration through the building envelope.
Industry data suggests homes with uninsulated, leaky duct systems in unconditioned attics can lose 25–30% of HVAC capacity to duct leakage. Sealing ducts is consistently one of the highest-return weatherization investments in the Northeast.
Combined blower door and duct blaster testing
For new construction code compliance, a combined test using both the blower door and the duct blaster simultaneously is the most efficient and accurate way to measure duct leakage to outside. We perform both tests in a single visit — setup, test, documentation, and report — so builders don't need to schedule two separate appointments before calling for final inspection.
Duct leakage testing for existing homes
Existing homes with high energy bills, uneven temperature between rooms, or comfort complaints that HVAC adjustments haven't resolved are often candidates for duct leakage testing. For homes with duct systems in unconditioned attics or crawlspaces, duct leakage is often a larger energy loss than envelope infiltration.
A duct leakage test on an existing home identifies the total leakage and, where possible, the dominant leak locations — so sealing work can be targeted rather than speculative. Post-sealing testing confirms the improvement.
Service area
dL Flow Tech performs residential duct leakage testing throughout the Hudson Valley and NYC metro: Dutchess, Westchester, Orange, Putnam, Rockland, and Ulster counties, the five boroughs, and surrounding communities. Based in Fishkill, NY.
Ready to test? Call (845) 265-2828 or request a quote. Combined blower door + duct blaster tests available in a single visit.
Frequently asked questions
- What is a duct blaster test?
- A duct blaster test uses a calibrated fan connected to the duct system to pressurize the ducts and measure how much air escapes through leaks. The result tells you — and the building department or HERS rater — how tight the duct system is.
- What is the difference between total duct leakage and leakage to outside?
- Total duct leakage measures all escaping air, including into conditioned space. Leakage to outside (Qn,out) measures only leakage to unconditioned spaces — attics, crawlspaces, garages. Energy codes limit Qn,out because that is the energy-penalty leakage.
- What is the New York State energy code requirement for duct leakage?
- The NY ECCC requires duct leakage to outside (Qn,out) ≤ 4 CFM25 per 100 sq ft of conditioned floor area, or total leakage ≤ 12 CFM25 per 100 sq ft. Testing must be by a qualified third party.
- Can the duct blaster test be done at the same time as the blower door test?
- Yes — and we do combined testing routinely. One visit, both tests performed, one report. More efficient and less expensive than two separate appointments.
- What does duct leakage mean for my energy bill?
- Duct leakage to outside is conditioned air dumped into unconditioned spaces. Industry estimates suggest 20–30% of heating and cooling energy is lost to duct leakage in homes with leaky duct systems — one of the highest-impact weatherization issues to fix.
Last updated June 2025