How to Brief a Ventilation Designer

How to brief a ventilation designer, step by step

1. Lead with the menu and the appliance schedule. The single most useful thing you can hand a designer is a full list of cooking appliances with their plan dimensions, fuel type and duty - light, medium or heavy. DW/172, the BESA specification that underpins UK kitchen ventilation, sizes extract from the appliances themselves using the thermal convection method, so a chargrill, a solid-top range and a bain-marie all pull very different air volumes. If the menu is likely to change, say so now, because designing for the busiest possible line is far cheaper than retrofitting later.
2. Name the standards you expect the design to meet. State plainly that you want the system designed to DW/172 (2018), with canopy and hood construction to the relevant parts of BS EN 16282, gas safety to BS 6173:2020, and grease handling that will pass a TR/19 clean. Writing the standards into the brief stops a designer quietly defaulting to a cheaper air-changes rule of thumb, which DW/172 itself discourages as a primary method. It also gives you a clear yardstick at commissioning and hand-over.
3. Describe the space and the building it sits in. Give ceiling heights, the position of structural steel, where the plant can go and how far the duct must travel to reach outside air. A short, straight duct run behaves very differently from a long route with several bends, and the designer needs to know the constraints before promising a fan size or a noise level. Flag any listed fabric, shared walls or neighbours whose windows sit near your proposed discharge point.
4. Set out make-up air and pressure from the outset. For every cubic metre you extract, roughly the same volume has to be replaced, or the kitchen goes into negative pressure and doors become hard to open while combustion appliances starve of air. Tell the designer how replacement air will arrive - tempered supply, transfer air from front of house, or ambient through louvres - and that you expect the make-up to be balanced against the extract, commonly around 85% mechanically supplied. Under-supplied kitchens are one of the most common causes of nuisance draughts and cold spots.
5. Specify cleaning access and grease management. Ask for the duct to be designed to TR/19 grease standards, with access doors at every change of direction and at spacings that let a technician reach the whole internal run. Keeping duct velocities high enough to carry grease along rather than let it settle, typically in the 7.5 to 10 m/s range, is a design decision, not an afterthought. A system that cannot be reached cannot be cleaned, and an uncleanable duct is both a fire risk and an insurance problem.
6. Fix the interlocks, controls and fire strategy. Where you cook on gas, BS 6173 requires a gas interlock so the appliances cannot fire unless the extract is proven to be moving air, usually through an air-pressure differential switch. Make clear whether you want variable-speed control tied to demand, how the canopy integrates with any fire suppression under BS EN 16282-7, and how the system should behave on fan failure. These are safety-critical decisions that are far cheaper to specify now than to bolt on afterwards.
7. Say how the system will be run, maintained and signed off. Tell the designer who will operate the controls, how often the kitchen runs and what your planned cleaning frequency will be, because a heavy-use fryer line needs a very different maintenance regime from an occasional function kitchen. Ask for a commissioning record with measured air volumes, a clear operation and maintenance manual, and duct access marked up on a drawing. That paperwork is what your insurer, your environmental health officer and your future cleaning contractor will all ask to see.

What a good brief unlocks in return

Once the designer has the information above, the conversation stops being a guessing game and becomes engineering. Expect them to come back with a calculated extract volume - for medium to heavy duty cooking that usually lands around 0.4 to 0.6 m³/s per metre of canopy length - together with a fan selection, an estimated noise level and a proposed duct route. If any of those numbers feels wrong for your space, this is the moment to challenge them, while everything still lives on a drawing rather than on a wall. A designer worth their fee will happily talk you through the assumptions behind each figure.

A thorough brief also forces coordination that is easy to forget. Kitchen extract rarely sits on its own - it shares plant space, risers and sometimes a facade with other building systems, and in larger premises it has to be reconciled with the life-safety strategy. If your building has mechanical smoke ventilation, the two systems must not fight each other, and it is worth reading how smoke control and everyday ventilation interact before you finalise anything. Getting the make-up air right matters beyond the kitchen too, because poorly supplied or unbalanced ventilation drives condensation into surrounding spaces, which is exactly the mechanism behind mould problems in commercial buildings.

There are a few red flags to watch for in the designer's response. Be wary of any scheme sized purely on air changes per hour, of a duct route with no access doors shown, of a make-up air strategy that amounts to leaving the back door open, and of a gas kitchen with no interlock detailed. None of these will pass a serious commissioning check, and all of them tend to surface as running problems within the first year. Push for the design to be captured as a proper specification with drawings, calculations and a commissioning target, so there is something concrete to test the finished installation against.

Finally, treat the brief as a living document rather than a one-off email. As the fit-out develops, appliances get swapped, ceilings drop and plant positions move, and each of those changes ripples back into the ventilation numbers. Keep the designer informed as decisions firm up, and insist that the final commissioning record reflects the kitchen as actually built, not as first imagined. That single habit is the difference between a system you fight for years and one that simply does its job quietly in the background.