Make-Up Air in Commercial Kitchens

Why does a kitchen need make-up air at all?

Because a fan is a pump, not a vacuum. It moves air along a path, and a path needs both ends. Take 2 m³/s out of a sealed room and the fan spends its energy pulling against the room rather than moving air through the canopy. Real kitchens are never sealed, so what happens instead is quieter and worse: the fan finds its own supply through the gaps around the back door, the cellar hatch, the dining room and, on a bad system, a flue.

Nothing about that shows up as an obvious fault. The canopy still looks right, the fan still sounds right, and the kitchen slowly gets used to smoke hanging under the canopy at the busiest hour.

How much make-up air does a kitchen need?

The figure the UK trade designs to is up to 85% of the extract volume, and it is commonly attributed to DW/172. Treat it as the convention it is. DW/172 is a paid specification and no source could be found that carries the 85% with a clause reference against it, so the honest description is a widely used design rule rather than a quoted requirement. If a designer states it as a clause, the fair question is which clause.

The reason the number sits below 100% is physical rather than conventional. Supplying less air than you extract leaves the kitchen slightly below the pressure of the rooms next to it, so air moves into the kitchen and out through the canopy rather than the other way round. Food hygiene law asks for the same behaviour in different words: mechanical airflow from a contaminated area to a clean area is to be avoided. Supply 100% and the kitchen is free to push cooking smells into the dining room. Supply far too little and every symptom below appears.

Balance is measured, not assumed. The number that matters on a commissioning sheet is extract and supply measured on the same day against the design figures, not the rating plates on two pieces of equipment.

Where should make-up air come in?

Four routes, and the choice usually comes down to what the building can accommodate rather than what the kitchen would prefer.

Whichever route is used, the supply has to arrive slowly and away from the cooking plume. A canopy captures a rising column of hot air, and a supply jet aimed across that column disperses it into the room. This is the failure mode that produces a kitchen with a correctly sized canopy, a correctly sized fan, a supply system, and smoke at the pass.

What is a make-up air unit?

A packaged unit with its own fan, filtration and, in most UK installations, a heater battery, ducted to deliver replacement air into the kitchen and wired to run with the extract. The heater is the reason it exists. Untempered outside air arriving at a cooking line in winter is a working conditions problem, and workplace law expects a reasonable indoor temperature, normally at least 16°C, or 13°C where the work involves rigorous physical effort.

Which is why the supply half of a system is the half that gets sabotaged. A louvre that blows cold air at the pass gets taped over in the first cold week, and from then on the kitchen has an extract system with no supply and nobody remembers that it once had one.

What does the damper do?

A motorised damper on the supply opens when the system runs and closes when it stops, so the kitchen is not left with an open hole to outside overnight. On an interlocked system the damper position is often part of what the control has to see before it will let anything else start. A damper stuck closed produces the exact symptoms of no make-up air on a system that has one, which is worth knowing before anybody replaces a fan.

How do I know my kitchen has a make-up air problem?

Six symptoms. Any one of them on its own can have another cause. Three of them together rarely does.

The cheapest test is the crudest one. Prop the kitchen door open, run the extract, and see whether the kitchen suddenly clears. If it does, the fan was never the problem: the room was.

Can make-up air be added to an existing kitchen?

Usually, and what decides the cost is the route rather than the equipment. A wall with an outside face and space above the ceiling is a straightforward retrofit. A basement kitchen in a listed terrace with one external wall already carrying the extract discharge is a different conversation, and it is the one where a survey pays for itself before a quote exists.

No installation price appears on this site, and that is deliberate. The published ranges for a supply and install contradict each other by a factor of ten, and measuring your kitchen is a better use of an hour than repeating somebody else’s number. How we approach an installation. See also the DW172 ductwork standard and why a commercial kitchen gets too hot.