Commercial Kitchen Make-Up Air Explained

Commercial kitchen make-up air—also called replacement air—is the air introduced to replace what the extract system removes. Without a controlled replacement-air strategy, the kitchen can become excessively negative, causing draughts, difficult doors, poor canopy capture and potentially unsafe interaction with gas appliances or flues.

Why extraction creates a building-wide issue

An extract fan does not create air; it moves it out of the building. If replacement air is not deliberately supplied, air will be pulled through whatever routes are available:

  • external doors and gaps;
  • serving hatches;
  • toilets and waste areas;
  • dining rooms;
  • neighbouring tenancies;
  • service risers;
  • chimneys and flues.

Those uncontrolled paths can create hygiene, comfort, energy and combustion-safety problems.

The kitchen usually needs some pressure relationship

Commercial kitchens are often kept slightly negative relative to cleaner adjacent areas so cooking smells do not migrate into dining or circulation spaces. “Slightly negative” is not the same as maximally negative.

The desired relationship must be designed across the whole building. Extract systems in toilets, bars, dishwash areas and neighbouring units can all influence it.

Doors being held shut by pressure is not proof that the extract is powerful and successful. It can be evidence that the system balance is wrong.

Common symptoms of inadequate replacement air

  • external doors are hard to open or slam shut;
  • strong cold draughts cross the cookline;
  • smoke or steam escapes from the canopy;
  • the dining room smells when the kitchen starts;
  • staff prop open doors to make the system behave;
  • fan noise changes when a door opens;
  • pilot lights or combustion appliances behave irregularly;
  • condensation or excessive heat remains despite high fan noise;
  • air is pulled from toilets or waste areas;
  • the measured extract flow is below the design duty.

These symptoms need investigation, not a bigger extract fan by default.

Natural make-up air versus mechanical supply

Replacement air can enter through designed passive openings or a mechanical supply system. The choice depends on airflow, building layout, climate, comfort, noise, security and control requirements.

Passive provision

Purpose-designed openings can be simple, but their performance varies with wind and pressure. Large openings may create draughts, noise or security concerns and can be difficult to route in dense sites.

Mechanical supply

A supply fan can provide more controlled air quantity and distribution. It adds filters, controls, ductwork, energy use, heating/cooling considerations and maintenance.

Neither approach should be reduced to leaving a door open. The opening may be closed during cold weather, service or security incidents, immediately changing the safety and performance assumptions.

Where supply air enters matters

Replacement air should reach the occupied space and canopy without disrupting the cooking plume.

Poor distribution can cause:

  • high-velocity air across the canopy face;
  • draughts at staff level;
  • hot and cold spots;
  • short-circuiting directly into the extract;
  • contamination moving from dirty to clean zones;
  • poor performance when only some fans operate.

The HSE's kitchen ventilation guidance emphasises both removal of fumes and adequate air replacement. DW/172 provides the kitchen-specific industry framework.

Gas appliances make balance safety-critical

Gas appliances need combustion air and safe removal of combustion products. The pressure created by extraction can affect open-flued or canopy-flued equipment.

The gas engineer, ventilation designer and controls contractor need a shared design basis covering:

  • appliance type and heat input;
  • extract and supply air quantities;
  • flue or canopy arrangement;
  • interlock/proving strategy;
  • start-up and shutdown sequences;
  • other fans operating in the building;
  • commissioning under realistic conditions.

The HSE states that employers should ensure relevant gas supplies are interlocked with ventilation and that enough ventilation exists to remove combustion products: HSE gas safety for employers.

Heating and energy implications

Large volumes of outdoor air may need heating in winter and can increase cooling loads in summer. Energy-saving ideas must not compromise safe capture or ventilation.

Options such as demand-controlled kitchen ventilation require:

  • compatible appliances and controls;
  • a defined minimum safe operating condition;
  • reliable sensing;
  • coordinated extract and supply modulation;
  • gas interlock compatibility;
  • commissioning across operating modes;
  • a maintenance and fault strategy.

Turning fans down without proving containment and safety is not a control strategy.

Survey questions

Record:

  • all extract and supply fans serving the tenancy;
  • proposed and existing airflow data;
  • outdoor-air intake options;
  • adjacent room uses and pressure relationships;
  • external doors and loading activity;
  • gas and other combustion appliances;
  • heating/cooling provision;
  • ceiling and riser routes;
  • noise-sensitive areas;
  • controls and interlocks;
  • how the building operates outside kitchen hours.

A shop within a larger development may depend on landlord air systems or pressure regimes. Obtain the base-build design information before fixing the tenant system.

Commissioning should test the real operating modes

Commissioning should not be limited to reading one fan at full speed. Test, as applicable:

  • extract and supply quantities;
  • room pressure relationships;
  • canopy capture/containment;
  • door operation;
  • minimum and maximum fan modes;
  • all relevant combinations of kitchen and building fans;
  • interlock operation;
  • performance with filters in their intended condition;
  • controls after power interruption;
  • staff-understandable operating instructions.

Retain results as the benchmark for future maintenance and fault finding.

Common mistakes

  • specifying extract before finding a route for supply air;
  • using transfer air from an unsuitable or dirty area;
  • directing supply jets at the canopy;
  • omitting winter comfort and heating capacity;
  • letting the landlord and tenant designs use conflicting air assumptions;
  • balancing with doors propped open;
  • adding odour filters without checking the changed operating point;
  • changing fan speeds after commissioning without retesting gas interlocks and capture.

Coordinate air, equipment and room layout

The KIG 317 Commercial Kitchen Installation Guide helps teams identify replacement air, services and coordination requirements while the layout is still changeable.

Sources and further reading

This is general guidance, not an airflow calculation or gas-safety assessment. A competent designer must establish supply, extract and pressure relationships for the actual building and appliances. Last reviewed: 13 August 2026.