Short answer: Some proprietary recirculating systems are designed for defined electric appliances and cooking duties, but recirculation is not suitable as a general substitute for external discharge. Heat, moisture, grease, smoke, gaseous odour and—where combustion occurs—combustion products must all be addressed under product, building, fire, workplace and local-authority requirements.
A recirculation unit returns treated air to the occupied building. Any pollutant not captured remains indoors, and filter failure affects staff and customers rather than only the external plume. The proposal therefore requires a clearly bounded appliance/menu duty, multi-stage filtration, monitoring, maintenance and replacement air/general ventilation strategy.
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.
Start with the appliance and fuel restrictions
A proprietary ventless hood may be certified or approved only for listed electric appliances and loads. Gas and solid-fuel combustion introduce products that must not be assumed treatable by recirculating odour filters. Follow the unit and appliance manufacturer’s exact limitations.
- Approved appliance models and power.
- Electric-only restriction where stated.
- Maximum cooking duty and food type.
- Fire suppression or interlock requirements.
- Prohibited fuels and operations.
Account for heat and moisture
Particle and carbon filters do not remove all sensible heat or water vapour. Cooking, washing and people still add loads to the room. The mechanical and comfort design must show how temperature, humidity and general air quality remain acceptable throughout peak operation.
- Heat gain from appliances.
- Steam and moisture release.
- General ventilation and cooling capacity.
- Condensate management.
- Room pressure and transfer air.
Treat failure as an indoor-air event
Recirculation needs visible status, defined filter-change triggers and controls that prevent cooking outside the approved operating condition. Grease filters, fine filters and carbon must remain correctly fitted. Operators need an immediate plan for alarms or odour breakthrough.
- Filter presence/pressure monitoring where provided.
- Interlock to approved appliances.
- Planned media replacement.
- Indoor odour/air-quality complaint response.
- No bypass operation.
What the observation may be telling you
| Observation | What it may mean | Correct next step |
|---|---|---|
| Listed electric appliance within approved duty | Recirculation may be technically feasible | Verify full product/site requirements |
| Gas or solid-fuel appliance | Combustion products create major safety issue | Use specialist externally discharged design |
| High steam production | Humidity/condensation may remain | Provide suitable ventilation and moisture control |
| No filter alarm or maintenance plan | Failure can affect occupied room | Do not rely on unmanaged recirculation |
| Menu likely to change | Approved duty can be exceeded | Use strict change control |
A practical evidence workflow
Planning evidence and commissioning evidence answer different questions but should describe the same installed system. The first explains why the proposal should control impact; the second proves what was actually fitted and how it performed on the day of test.
- Freeze the operating brief. Record appliances, fuel, menu, hours, peak demand and delivery constraints. Note assumptions that may change, such as a future chargrill or later opening hours, because they can alter both treatment duty and planning risk.
- Issue a coordinated specification. Align the drawings, equipment schedule, treatment stages, duct route, discharge, access, acoustic measures, utilities, controls and maintenance requirements. Assign responsibility for every interface.
- Inspect before concealment. Photograph labels, access panels, fire-rated penetrations, drains, isolators, controls and service clearances. Resolve substitutions against the approved performance requirement rather than accepting a similar-looking unit.
- Commission and close out. Measure airflow and relevant pressure, electrical, water, gas, temperature or control values. Record test conditions, instruments and defects. Retest corrective work and provide the operator with the final evidence set.
Keep a useful record: Use a controlled index for drawings, calculations, product data, approvals, test sheets, certificates, photographs, training and maintenance information. Mark superseded versions clearly. A concise, traceable pack is stronger than hundreds of unindexed pages.
Project or service checks
- Obtain the proprietary system’s approved appliance list.
- Confirm fuel and duty restrictions.
- Calculate room heat and moisture loads.
- Define filtration stages and replacement triggers.
- Coordinate fire and appliance interlocks.
- Obtain building control/local-authority input.
- Train staff not to bypass alarms or filters.
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
- Calling a carbon hood equivalent to external extraction.
- Using an unapproved fryer or griddle beneath the unit.
- Ignoring heat and humidity.
- Removing filters to restore airflow.
- Allowing tenant menu changes without review.
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 gas cooking be recirculated?
Do not assume so. Combustion products require safe ventilation, and many proprietary recirculation systems are limited to specific electric appliances.
Does recirculation avoid planning permission?
It may reduce external plant, but change of use, noise, building and food-premises requirements can still apply. Check locally.
Are ventless hoods maintenance free?
No. Their performance depends heavily on filter cleaning/replacement, controls and staying within the approved cooking duty.
Related Kitchen Install Guide reading
- Commercial Kitchen Equipment Duty Categories
- Commercial Kitchen Make-Up Air Explained
- Planning Permission for Kitchen Extraction UK
Plan the whole commercial kitchen, not one isolated component
Use the Commercial Kitchen Install Guide to coordinate extraction, equipment, utilities, drainage, safety, access and handover before work reaches site.
Sources and further guidance
- BESA: DW/172 Specification for Kitchen Ventilation Systems
- HSE: Ventilation of kitchens and catering establishments
- HSE: Gas safety in catering and hospitality
- Purified Air: Commercial kitchen multi-filter units
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.