Analyze infiltration from airflow, volume, pressure, and leakage. Switch units, methods, and reporting without confusion. Build smarter upgrades with fast calculations, visuals, and downloads.
Choose a method, enter your building dimensions, and the calculator will estimate natural infiltration flow, ACH, normalized leakage, and annual air volume.
These sample cases illustrate how different test methods and assumptions can change the reported natural infiltration rate.
| Scenario | Method | Floor Area | Height | Volume | Key Input | Estimated Natural ACH |
|---|---|---|---|---|---|---|
| Office Retrofit | Direct airflow | 250 m² | 3.2 m | 800 m³ | 480 m³/h | 0.600 |
| Warehouse Bay | Blower-door with N-factor | 420 m² | 6.0 m | 2,520 m³ | 2,400 CFM @ 50 Pa, N = 20 | 0.081 |
| Small Retail Unit | Blower-door with power law | 140 m² | 3.4 m | 476 m³ | 1,100 CFM @ 50 Pa, n = 0.65, P = 4 Pa | 0.415 |
1) Building volume
V = Floor Area × Ceiling Height
2) Direct measured airflow method
ACH = Q / V
3) Blower-door conversion with N-factor
ACH50 = Q50 / V, then ACHn = ACH50 / N
4) Blower-door conversion with power law
Qnat = Q50 × (Pnat / 50)n, then ACH = Qnat / V
5) Time-based air volume
Daily Volume = Qnat × Hours/Day, Annual Volume = Daily Volume × Days/Year
Keep units consistent during calculations. This file converts entered values internally so the reported outputs remain comparable.
Infiltration rate is the amount of outside air entering a building through cracks, joints, and small openings over time. It is commonly reported as ACH, CFM, L/s, or m³/h.
Direct airflow uses measured operating leakage under natural or known conditions. Blower-door testing measures envelope leakage at a reference pressure, usually 50 Pa, then converts that result into an expected natural infiltration rate.
ACH means air changes per hour. A value of 0.50 means a volume of outside air equal to half the building volume enters each hour under the chosen assumptions.
N-factor converts ACH50 into an estimated natural ACH. Lower N-factors produce higher natural infiltration. Use a value appropriate for climate, building exposure, and the testing guidance applied to your project.
The pressure exponent describes how leakage flow changes with pressure. Many buildings fall near 0.60 to 0.70. Measured test data is better than a generic assumption whenever it is available.
Not always. Lower leakage usually improves comfort and energy performance, but buildings still need intentional ventilation for indoor air quality, moisture control, and occupant health.
Normalized flow helps compare buildings of different sizes. It shows leakage intensity rather than only total flow, which is useful during retrofit planning, benchmarking, and envelope design review.
Use it for planning, screening, and documentation support. Final compliance decisions should follow the exact local code, test standard, required pressure conditions, and reviewer instructions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.