Commercial Kitchen Canopy Sizing and Overhang

A commercial kitchen canopy must be large and correctly positioned enough to capture and contain the full cooking plume under real operating conditions. There is no safe universal overhang number for every appliance and hood. Wall or island position, appliance duty, door opening, side exposure, mounting height, replacement air and cross-draughts all affect the design.

Why the canopy is larger than the cookline

Hot contaminated air rises and expands as it leaves an appliance. It can also move sideways due to room currents, operator movement and the opening of oven doors.

The canopy capture zone therefore normally needs to extend beyond the physical edge of the source. The amount and direction of projection should be established using the current design specification and appliance information.

Copying a standard-looking dimension from another kitchen can fail when:

  • the new equipment has a higher duty;
  • an oven door releases a forward plume;
  • appliances sit further from the wall;
  • the canopy is mounted higher;
  • one or more sides are exposed;
  • supply air blows across the plume;
  • equipment moves on castors outside the intended position.

Wall canopies and island canopies behave differently

A wall helps contain the plume and reduces exposure on one side. An island canopy is exposed to air movement around more edges and often needs a different capture strategy.

Other arrangements include:

  • back-to-back island cooklines;
  • pass-over or front-of-house cooking;
  • low-level or proximity extraction;
  • ventilated ceilings;
  • dedicated condensate hoods for steam-producing equipment;
  • appliance-integrated ventilation.

The hood type must suit the emission source. A condensate hood designed mainly for steam is not automatically a grease extract canopy.

Start with an accurate appliance schedule

The designer needs more than approximate blocks on a plan. Record:

  • manufacturer and model;
  • dimensions and height;
  • gas, electric or solid-fuel operation;
  • rated input and cooking duty;
  • door, lid or loading direction;
  • whether the appliance is fixed or movable;
  • manufacturer ventilation and clearance requirements;
  • likely use during peak service;
  • future appliances the operator intends to add.

Combination ovens, pressure steamers and pizza ovens can release concentrated plumes when doors open. Fryers, woks and chargrills produce different grease, heat and smoke loads. Those differences affect hood geometry as well as airflow.

DW/172 is the main kitchen-ventilation reference

BESA's DW/172 is the recognised specification for commercial kitchen ventilation systems. It addresses appliance-based airflow assessment, canopy design, grease separation, replacement air, controls, ductwork and commissioning.

The current publication is the second edition from 2018 incorporating a May 2024 addendum. Use the actual specification for design. Do not rely on a blog that reproduces one old dimension without its conditions or context.

Airflow and geometry have to work together

A larger fan cannot reliably compensate for a badly positioned canopy. Similarly, a generous canopy can spill fumes if airflow is too low or disrupted.

Capture depends on:

  • plume volume and momentum;
  • canopy dimensions and mounting height;
  • extract air quantity;
  • filter arrangement and pressure drop;
  • room air movement;
  • replacement-air quantity and distribution;
  • adjacent walls or side panels;
  • operator movement and door opening;
  • system cleanliness and actual fan performance.

This is why “air changes per hour” is not enough for a local capture design. General ventilation and source capture solve different problems.

Replacement air can help or destroy capture

Supply air should replace extracted air without blowing the cooking plume out of the capture zone.

Common problems include:

  • high-velocity grilles directed at the canopy face;
  • ceiling diffusers creating cross-currents;
  • open doors beside the cookline;
  • excessive air introduced through the canopy perimeter;
  • a kitchen kept so negative that uncontrolled draughts dominate airflow.

Observe the room under realistic conditions. A smoke-visualisation or containment test carried out safely by competent people can reveal problems that are not obvious from a drawing.

Physical details that are often missed

Oven-door opening

The plume may project forward as the door opens. The canopy arrangement must consider the opening path and operator position.

Mobile equipment

Castors make cleaning easier but also allow an appliance to move outside the designed capture position. Use correct restraints and clear position marks where relevant.

Filter access

Filters need to be removable without unsafe lifting or obstructing nearby equipment. The plenum also needs appropriate drainage/cleaning consideration.

Lights and services

Lighting, fire-suppression pipework and services should not disrupt filters, access or cleanability.

Ceiling and structure

The canopy, duct and services require coordinated supports. Do not assume the ceiling grid or decorative lining can carry them.

Combustible surfaces

Appliance and building fire-clearance requirements must be addressed separately from capture geometry.

What to ask the canopy designer

  1. Which edition of DW/172 and other documents form the design basis?
  2. What exact appliance schedule was used?
  3. How were extract air quantities established?
  4. How were door-opening and exposed-edge plumes considered?
  5. Where does replacement air enter and at what velocity?
  6. Which filters are proposed and at what operating condition?
  7. What external resistance has been allowed for?
  8. How are the canopy, duct and services supported?
  9. How will capture and containment be commissioned?
  10. What changes would invalidate the design?

Common site changes that require review

  • swapping a boiling appliance for a fryer;
  • adding a chargrill or wok range;
  • changing fuel;
  • pushing equipment forward to clear services;
  • raising the canopy;
  • adding shelving beneath the hood;
  • changing the supply-air grilles;
  • adding dense filtration without checking the fan;
  • removing side panels;
  • extending operating hours or production intensity.

Plan canopy and cookline together

The KIG 317 Commercial Kitchen Installation Guide helps teams coordinate appliance positions, extraction, utilities, access and installation information before the canopy becomes a fixed constraint.

Sources and further reading

This article explains design considerations and intentionally does not reproduce DW/172 design tables. A competent ventilation designer must size the canopy and airflow for the actual appliance schedule and room. Last reviewed: 13 August 2026.