Quantify airflow leaks and their operational cost quickly. See energy, carbon, and severity instantly. Improve comfort, reduce bills, and protect project budgets.
| Scenario | Airflow (CFM) | Leak (%) | Hours (cool/fan) |
|---|---|---|---|
| Retail fit-out | 1,200 | 10 | 700 / 1,200 |
| Office mid-rise | 1,800 | 12 | 900 / 1,400 |
| Warehouse office | 2,400 | 18 | 600 / 1,800 |
Use these as starting points, then refine with site-specific hours and tariffs.
Unsealed joints, torn flex, and unbalanced returns can waste a measurable share of delivered airflow. A 12% leak on a 1,600 CFM system equals 192 CFM escaping to ceilings or shafts. That lost flow reduces zone air changes and can increase complaints, especially during commissioning and seasonal switchover. Leakage can pull dusty air into returns, increasing filter loading.
This calculator converts leaked airflow to mass flow, then estimates thermal load using air density 1.2 kg/m³ and Cp 1.006 kJ/kg·K. With a 17°C cooling temperature difference and 900 cooling hours, even modest leakage can add hundreds of kWh. Lower equipment COP amplifies electrical impact and may push peak demand. With fixed capacity, sensible delivery drops with reduced delivered airflow.
Fans often run longer than conditioning hours. The tool applies a planning value in W/CFM to approximate the electrical penalty of moving air that never reaches occupied zones. Leakage also distorts measured terminal flows, causing over-throttling at branches, higher static pressure, and increased noise. These effects can hide until testing. A small leak near the fan can cascade into oversized fan speed and unstable control at low loads.
Use measured leakage percentages from duct testing or inferred values from TAB reports and pressure maps. Record operating hours from controls trends, not nameplate assumptions. Export the results as CSV for submittals and as PDF for closeout packages, linking each scenario to drawing references, zones, and corrective actions. Include pre and post repair readings so the owner can verify savings claims later.
Prioritize sealing upstream of VAV boxes, at riser transitions, and around access doors. Replace degraded tape with mastic or approved sealant, and verify insulation integrity to prevent condensation. After repairs, recheck delivered CFM and re-run the calculator to quantify savings, then update the commissioning log. For renovation work, schedule smoke checks and quick pressure tests before ceilings close, reducing costly rework.
Start with 10–15% for typical installed ductwork, then refine using TAB airflow shortfalls, pressure readings, and visual inspection. Use higher values for older systems or poor access conditions.
No. It estimates sensible thermal impact using temperature difference only. If leakage draws humid air into conditioned spaces, actual cooling energy may be higher than this planning estimate.
It is a simplified fan energy intensity that converts leaked airflow into wasted fan kWh. You can approximate it from measured fan power divided by delivered airflow, or use a conservative default.
If ambient temperature is above the supply temperature, the heating temperature difference becomes zero in this model. Enter winter ambient conditions and heating hours to evaluate heating-season leakage.
Run the calculator twice with the same hours, tariffs, and temperatures. Change only the leakage percentage or airflow to reflect measured improvement, then compare total kWh and cost results.
Yes. Attach the CSV/PDF output to your closeout package, alongside test reports and corrective action notes. Treat values as estimates unless backed by metered energy and verified operating hours.
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.