Short answer: An ESP can often be retrofitted, but it is not a simple matter of cutting a box into the duct. The existing system must be surveyed for real airflow, available fan pressure, duct condition, fire strategy, space, supports, electrical supply, controls, safe maintenance access and the intended odour-control outcome.
Retrofits commonly follow smoke complaints, a planning condition, a menu change or visible grease at the discharge. If the original extract is already underperforming, adding resistance or turbulence can make canopy capture worse. The upgrade should begin with measurements and drawings, not a product size guessed from duct dimensions.
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.
Survey the system in operation
Measure extract and replacement air, inspect canopy capture, confirm fan details and identify every existing filter, silencer, fire treatment and control. Record duct dimensions and route rather than relying on old drawings. Grease contamination, leakage or inaccessible sections may need correction before new equipment is added.
- Measured extract airflow and fan speed.
- Canopy capture observations under representative cooking.
- Duct cleanliness, leakage and access.
- Available static pressure and fan curve.
- Existing planning and fire information.
Coordinate physical and electrical installation
The ESP needs structural support, a service envelope, a cell-removal route and an isolatable power supply. Its controls normally need to prove extract operation so the unit does not energise without airflow. Roof or external locations introduce weather and safe-access requirements; ceiling locations create manual-handling and dirty-cell transport issues.
- Casing weight and support details.
- Lifting and delivery route.
- Electrical load, isolator and interlock.
- Access doors, lighting and safe standing area.
- Cleaning location and drainage arrangements.
Recommission the whole system
After installation, verify total airflow, branch balance, canopy containment, ESP operation, alarms and every related fan or gas interlock. Compare the readings with pre-retrofit measurements. The project is not complete when the casing is fitted; it is complete when the combined system delivers its intended duty and the operator has a maintenance plan.
- Measure extract and supply air.
- Function-test ESP enable and fault status.
- Confirm no unintended air leakage.
- Issue updated drawings and service instructions.
What the observation may be telling you
| Observation | What it may mean | Correct next step |
|---|---|---|
| Existing fan has pressure reserve | Retrofit may be feasible without fan replacement | Verify at the new system operating point |
| Fan already at maximum and airflow low | Added equipment may worsen capture | Resolve fan/system deficiency first |
| No cell withdrawal space | Maintenance will be impractical | Change location or create proper access |
| Duct heavily contaminated | Fire and performance risks pre-exist | Clean, inspect and repair before installation |
| Complaint is mainly gaseous odour | ESP alone may not meet the objective | Specify a complete treatment and dispersion solution |
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 a pre-retrofit airflow and condition report.
- Confirm what pollutant the upgrade is intended to control.
- Check fan curve and new total resistance.
- Review planning conditions and fire strategy.
- Show support and service access on coordinated drawings.
- Design safe electrical isolation and fan interlocking.
- Require full recommissioning and updated 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 from duct width alone.
- Installing onto a dirty or leaking extract system.
- Assuming the existing fan will absorb extra resistance.
- Treating the retrofit as an odour guarantee.
- Leaving the operator without a cell-cleaning arrangement.
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
Does an ESP retrofit require planning permission?
The internal equipment may not by itself, but changes to external plant, noise, discharge or an existing planning condition can require review with the local authority.
Must the kitchen close during installation?
That depends on access, isolation and hygiene controls. Work on a grease extract and electrical system normally requires a planned shutdown and safe work area.
Should the duct be cleaned first?
A condition inspection and, where necessary, cleaning are sensible so the new system is installed into a known and maintainable extract path.
Related Kitchen Install Guide reading
- Commercial Kitchen Site Survey Checklist
- Best Route for Commercial Kitchen Extract Ductwork
- 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: Duct design and ESP performance
- GOV.UK: How councils deal with nuisance smells
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.