Short answer: Airflow determines how quickly contaminated air passes through an ESP and therefore influences particle-charging and collection opportunity. Too much air through too little effective cell area can reduce performance; too little extract air can undermine canopy capture before the air even reaches the ESP.
The extract system has two linked duties: capture contaminants at the cookline and pass them through treatment equipment within its operating range. Selecting an ESP at a headline maximum airflow without checking the calculated duty, diversity, fan curve, duct resistance and commissioning measurements can fail at either end of that chain.
Important: This guide explains design questions; it is not a product selection, planning approval or performance guarantee. A competent designer should assess the actual kitchen, air system, discharge and maintenance conditions.
Face velocity and collection opportunity
The same volume through a smaller collector face produces a higher velocity. Higher velocity reduces residence time and may carry more particles through the collector. Manufacturers define operating limits for their cells and housings; the designer should use those limits rather than inventing a universal number.
- Use the actual duty in cubic metres per second or litres per second.
- Check effective cell face area, not only casing dimensions.
- Allow for all operating modes where variable-speed control is used.
- Confirm cell configuration matches the selected airflow.
Airflow is set by the complete resistance
The fan operates where its performance curve meets the resistance of the real system. Duct length, bends, filters, attenuators, ESP cells, carbon stages and terminal losses all contribute. If late treatment is added without reselecting the fan, the delivered airflow may fall below the canopy design value.
- Calculate clean system resistance.
- Allow a rational loaded-filter condition.
- Record the selected fan operating point.
- Measure final extract and supply quantities after installation.
Balancing and bypass
Even when the total fan airflow looks correct, air may not be distributed evenly across parallel cells or branches. Gaps around cells, blank spaces and poor internal distribution allow untreated air to bypass the active surface. Commissioning should inspect the physical installation as well as taking duct and grille readings.
- Verify cells and blanking plates are fitted as designed.
- Check access doors and seals.
- Measure branch and total airflow where the layout can become unbalanced.
- Recheck after major filter or fan changes.
What the observation may be telling you
| Observation | What it may mean | Correct next step |
|---|---|---|
| Airflow above ESP range | High velocity and reduced collection opportunity | Increase cell area or revise duty with the designer |
| Airflow below canopy requirement | Poor capture, heat and fumes escaping into kitchen | Review fan duty, resistance and replacement air |
| Correct total but uneven cell loading | Internal distribution or bypass issue | Inspect housing, blanks and branch balancing |
| Airflow falls as filters load | Fan has insufficient reserve or maintenance is late | Define loaded condition and service trigger |
| Variable-speed system at low mode | ESP/control may be outside intended operating state | Commission every control mode and interlock |
A practical design and handover workflow
Treat the filtration unit as one component of an air system. A dependable design starts with the cooking process and ends with a maintainable discharge, rather than starting with a catalogue airflow. The following workflow gives the client, designer and installer a shared audit trail.
- Define the source. List every appliance, fuel, cooking method, duty, diversity assumption and operating period. Chargrilling, frying and light reheating do not create the same grease, smoke or odour load. Record the future menu where the tenant is not yet trading.
- Establish the air duty. Calculate the extract volume and capture arrangement, then record the expected operating range. Check make-up air, duct velocity, leakage class, fan curve and the resistance of clean and loaded treatment stages.
- Select the treatment train. State what each stage is intended to remove, the evidence used for selection and the conditions attached to any performance claim. Include bypass sealing, controls, interlocks, alarms and the effect of failure.
- Prove and maintain it. Commission airflow and functions at the installed condition. Give the operator baseline readings, access instructions, cleaning intervals, consumables and a clear trigger for inspection or replacement.
Keep a useful record: Keep the approved drawing, design airflow, fan duty, clean pressure readings, control cause-and-effect, commissioning results and maintenance log together. When performance changes, comparison with this baseline is more useful than replacing parts by guesswork.
Project or service checks
- Obtain the design extract volume and calculation basis.
- Request the ESP operating airflow range.
- Include every treatment stage in the resistance calculation.
- Coordinate extract and make-up air quantities.
- Commission high, low and demand-control modes.
- Measure actual airflow rather than relying on inverter frequency.
- Keep the final balancing report with the O&M information.
Turn the agreed checks into named deliverables. Each item should have an owner, due date and acceptance method. Where a measurement is required, record the value, unit, instrument or source, operating condition and result. This makes the information usable at handover and during a later investigation.
Common mistakes to avoid
- Sizing to a rounded kitchen-area rule without the appliance duty.
- Equating fan speed percentage with airflow percentage.
- Ignoring dirty-filter resistance.
- Allowing unsealed bypass around treatment cells.
- Commissioning the fan but not the ESP and controls together.
Avoid closing the issue on appearance alone. A new filter, reset controller or revised drawing may change the symptom without resolving the underlying duty, utility, access or maintenance problem. Confirm the completed work under a representative operating condition and keep the evidence with the asset or ventilation record.
Frequently asked questions
Can airflow be checked from the inverter display?
No. Frequency is an input to the motor, not a direct measurement of delivered air volume. The system needs suitable airflow measurements.
Will a larger fan improve ESP performance?
Not automatically. Excess airflow can harm treatment performance and create noise or capture problems elsewhere. The fan and ESP must be selected together.
Should airflow be rechecked after filter changes?
Routine replacement should restore the intended condition. A different filter grade, added stage or altered duct route should trigger a system review and recommissioning.
Related Kitchen Install Guide reading
- Commercial Kitchen Make-Up Air Explained
- What Is DW/172?
- What Should a Kitchen Extraction Quote Include?
Capture the installation and commissioning detail
Use the KIG 318 Commercial Kitchen Installation Checklist to record interfaces, checks, outstanding actions and the evidence needed at handover.
Sources and further guidance
- BESA: DW/172 Specification for Kitchen Ventilation Systems
- HSE: Ventilation of kitchens and catering establishments
- Purified Air: Commercial kitchen ESP systems
- Extechnology: Airflow rates and ESP performance
Last reviewed: 14 August 2026. This article provides general commercial-kitchen design information. It does not replace a site-specific ventilation design, manufacturer instructions, risk assessment, planning conditions or advice from a competent specialist.