What is ventilation commissioning?

Ventilation commissioning is the process of testing and adjusting a ventilation system to ensure it delivers the design airflow rates at each terminal. This involves measuring airflow at every supply and extract terminal with a calibrated flow hood or anemometer, comparing against the design values, and adjusting dampers until all terminals are within tolerance (typically ±10%).

What tolerance is acceptable for ventilation commissioning?

Approved Document F requires ventilation systems to be commissioned to within ±10% of the design flow rate at each terminal. BSRIA Application Guide AG3 recommends the same ±10% tolerance for most systems. Critical environments (operating theatres, cleanrooms) may require tighter tolerances of ±5%.

Who can commission a domestic ventilation system?

Under Part F, ventilation commissioning must be carried out by a competent person. For domestic installations, the installer is usually responsible. The results must be recorded on a commissioning sheet and a copy given to the building control body. For commercial systems, a specialist commissioning engineer is typically engaged.

What information should a commissioning record include?

A commissioning record should include: the ventilation system type, design flow rates for each terminal, measured flow rates, percentage deviation from design, fan speed settings, SFP measurement, the instrument used and its calibration date, the name and signature of the commissioning engineer, and the date of commissioning.

How do I measure airflow at a terminal?

Use a calibrated balometer (flow hood) placed over the diffuser or grille to directly measure the airflow in L/s. For small terminals, a rotating vane anemometer can be used to measure velocity, then multiply by the duct cross-sectional area. The instrument should be calibrated within the last 12 months per BSRIA guidance.

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Ventilation Commissioning Calculator — Flow Balance Check

Check ventilation system commissioning by comparing target vs measured flow rates at each terminal. Verify system balance within the required tolerance per ADF.

System Type

Number of Terminals

Target Flow Per Terminal

Or leave blank and enter total below

Total Target Flow

Divided equally if per-terminal not set

Measured Flow Rates (comma-separated, L/s)

Enter one value per terminal, separated by commas

How We Calculate This

This calculator compares target design flow rates against measured flow rates for each ventilation terminal to assess system balance and compliance.

Commissioning check

Enter the target flow rate per terminal (or total divided equally)
Enter measured flows as comma-separated values
Each terminal is checked against the ±10% tolerance
Overall system balance is verified

Pass/fail criteria

Each terminal must be within ±10% of its design flow rate (ADF and BSRIA AG3). The total system flow must also be within ±10% of the total design flow. Any terminal outside tolerance requires damper adjustment and re-measurement.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.