| Measured Airflow | Pressure (Pa) | Volume | Envelope Area | Expected ACH | Expected L/s·m² |
|---|---|---|---|---|---|
| 1200 CFM | 50 | 18,000 ft³ | 5,400 ft² | 4.00 | 0.52 |
| 650 L/s | 50 | 1,200 m³ | 900 m² | 1.95 | 0.72 |
1) Air changes per hour at test pressure
Convert airflow to m³/s. Convert volume to m³.
2) Area-normalized leakage
3) Equivalent leakage area
These equations provide consistent comparisons across projects and specifications.
- Enter the measured airflow from your enclosure test.
- Enter the test pressure used in the report.
- Add building volume and enclosure surface area.
- Keep units consistent with your measurement method.
- Adjust Cd and air density for improved ELA accuracy.
- Press Calculate to view results above the form.
- Download CSV or PDF for submittals and records.
Why leakage rate reporting matters on projects
Measured leakage turns air sealing into a verifiable deliverable for owners, lenders, and code officials. It supports commissioning, reduces comfort complaints, and improves moisture control at cold surfaces. When results are documented early, trades can coordinate interfaces, penetrations, and transitions before finishes conceal defects and rework becomes expensive. By tying results to acceptance criteria, teams can close gaps systematically, justify temporary enclosures, and demonstrate that the installed air barrier meets design intent at handover for tested zone.
Selecting inputs that reflect the true enclosure
Use conditioned volume that matches the pressure boundary, not the entire building shell. Exclude vented attics, crawlspaces, and shafts if they are outside the air barrier. Envelope area should align with your specification basis, whether gross exterior surface or a defined test boundary, so comparisons remain fair between phases and similar buildings.
Interpreting ACH and area-normalized leakage together
ACH expresses how quickly air is exchanged relative to volume at the test pressure, often 50 Pa. It relates to infiltration load sensitivity and how much uncontrolled air can bypass ventilation systems. Area-normalized leakage highlights surface quality, helping larger buildings compare performance even when volumes differ. Reviewing both metrics prevents one number from masking poor detailing.
Using equivalent leakage area to guide repairs
Equivalent leakage area converts airflow into an opening size at the stated pressure using Cd and air density. Field teams can visualize whether leakage resembles a few large gaps or many small cracks. A rising ELA frequently points to missing seals at curtainwall joints, slab edges, or mechanical sleeves. Retest after repairs to confirm durable improvement.
Turning results into a practical action plan
Start with smoke tracing, infrared scans, and pressure diagnostics to locate dominant pathways during pressurization and depressurization. Prioritize durable measures such as gasketed access panels, sealed sleeves, continuous membranes, and tested transition materials. Document corrective actions, then export the CSV or PDF to track revisions, compare zones, and support closeout, warranty, and energy model updates.
What does ACH at test pressure represent?
It is air changes per hour calculated from measured airflow and enclosure volume at the stated pressure. It helps compare airtightness across buildings and indicates potential infiltration and exfiltration impacts on energy use and comfort.
Which volume should I use for the calculation?
Use the conditioned volume inside the pressure boundary. Include spaces served by the HVAC system and exclude vented attics, unconditioned crawlspaces, or shafts that are outside the air barrier.
Why is area-normalized leakage useful?
Leakage per unit area reduces the influence of building size. It is helpful for comparing enclosures with similar detailing, tracking contractor performance, and checking targets written as L/s·m² or CFM/ft².
How is equivalent leakage area different from crack length?
ELA expresses the total leakage as an orifice area at the test pressure using Cd and air density. It does not locate leaks, but it helps visualize the combined size of openings that would pass the same airflow.
Can I change Cd and air density?
Yes. Use Cd that matches your method if specified, and adjust air density for altitude or temperature when you want a closer ELA estimate. ACH and area-normalized leakage are less sensitive to those settings.
When should I retest the enclosure?
Retest after major air-sealing work, after façade closures, or when results are near acceptance thresholds. Testing both before and after fixes confirms that improvements are real and supports closeout documentation.