Reading a CFD Ventilation Report for a Commercial Kitchen: What It Should Show Before You Accept It

The CFD report lands in your inbox as a PDF full of colour: red where the air is hot, blue where it is moving, arrows curling out of a hood. It looks like proof. It is not proof of anything until you know what was fed into the model and what question it was asked, and that is the part most kitchen owners never see.

This is a short guide to reading one. We model airflow for commercial kitchen ventilation at design stage and balance it at commissioning, so we know how easily a handsome report can say very little. None of what follows needs an engineering degree, and you can put every point to whoever produced the report, whether that is us or someone else.

First: what question was the model asked?

A useful study answers a specific question. "Will this hood capture the plume from this wok range at this height?" is a question. "Model the kitchen" is not, and a report built on the second tends to describe the room rather than answer anything about it.

The first page should say what the study set out to find out, in plain words. If you cannot tell from the opening page what decision the report was supposed to support, ask. We cover when a study is worth commissioning at all in when a CFD ventilation study is worth paying for; this article assumes you already have one in front of you.

Second: what went in?

A model only reports what it was told. Every result is a consequence of its inputs, and the inputs are where reports quietly differ. Look for a page or table that states:

• The design exhaust and make-up air figures. This is the single most important line. The model is run to those numbers, and the commissioning measurement is later compared against the same numbers. If the report never states them, there is nothing for anyone to be held to.
• The cooking equipment. Which appliances sit under the hood, where they are, and what heat they put out. A wok range and a steamer under one canopy do not behave alike, and the interaction between them is exactly what a model is good for.
• The room. The hood and canopy, the ceiling height, the doors and openings, and where the make-up air actually enters. A model of a sealed empty box says little about a kitchen with a pass window and a door to the dining room.
• The conditions assumed. Which appliances are running at once, whether doors are shut or open, and whether the make-up air is on. If the report only models the best case, it has not tested the system.

Ask for these in writing, on the page, not in a covering email. A study with no stated inputs cannot be checked by anyone later.

Third: what did it actually show?

The pictures should answer the question from the first page. For a commercial kitchen that usually means a handful of things:

• Capture at the hood. Does the plume from each appliance get drawn in, or does some of it escape past the edge of the canopy? This is the heart of the matter for a cooking line, and it is the same capture the air balancing step later verifies on the finished system.
• Where the air goes outside the hood. Heat and smoke that miss the hood do not disappear; they travel. A good report shows where they end up, including towards the dining area.
• The pressure between kitchen and dining. Whether the kitchen is pulled negative, and what that does to doors and to the air-conditioned side. This is the same family of symptoms we describe in make-up air and air balancing: doors that slam, smell in the dining area, air-conditioning fighting the exhaust.
• Where the make-up air arrives. Make-up air thrown straight across the hood face can disturb capture. A report that never mentions where the replacement air enters is skipping half of the system.

Colour plots are fine, but each one should be labelled with what is being shown and where the slice was taken. A plot with no label tells you nothing you can use.

Fourth: how many scenarios?

A kitchen is never in one state. One run of one condition is a snapshot. Ask which cases were modelled and which were left out. A sensible set covers the busy case with the main appliances running together, a quieter case, and at least one awkward one, such as a door open to the dining room or the make-up air reduced. The awkward case is where a marginal design shows itself, and it is the one a tidy report is most tempted to leave out.

On a live fit-out the layout changes, and a model that was right for the first drawing may not be right for the last. That is one reason we run the modelling ourselves: when an appliance moves or a duct route changes, the scenario can be re-run quickly rather than waiting on an outside consultant. Ask whoever produced your report what happens to the study when the drawings change, because on most projects they will.

Fifth: what changed because of it?

The test of a study is not the report. It is whether the design was different afterwards. A model that finds nothing to change is possible, but it is worth asking: did the hood position, the make-up air route or the duct layout move as a result? If every finding says "no change needed", ask what the model was able to disprove.

The best reports end with a short list: what the model found, what was changed on the drawings, and what is still to be confirmed on site. That last item matters most.

Where the report ends and the site begins

A model predicts. It does not prove the finished kitchen. The proof is the commissioning measurement: once the system is installed, the exhaust and make-up air are measured and adjusted to the design figures, the hood capture is verified over the cooking line, and the pressure between the kitchen and the dining area is corrected.

That is why the design figures in the report matter so much. They are the numbers the measurement is held against. A system that was modelled but never balanced is a theory, and a system balanced with no design figures to balance to is guesswork with a meter in its hand. Before you accept the report, check three things with whoever is doing the work:

1. Is balancing in the programme, with a date? It belongs on the schedule, not in the goodwill at the end of the job.
2. Will you receive the measured figures? Ask for them, and keep them next to the report. They are the baseline for any complaint later.
3. Do the measured figures get compared with the report's design figures? If nobody plans to put the two side by side, the study and the site are not connected.

If you are taking over a newly built kitchen, the same documents belong in your handover pack. We list what to ask for in new kitchen exhaust handover: the readings and documents to ask for.

Warning signs in a CFD report

• No stated airflow figures, so nothing to balance to.
• Only one scenario, and it is the easy one.
• The model leaves out the doors, the pass window or the make-up air route.
• Plots with no labels and no stated slice position.
• No link to the drawings: it is unclear which version of the layout was modelled.
• A confident conclusion with no list of what is still to be verified on site.

None of these means the engineer was careless. They mean the report cannot yet be relied on, and the fix is usually a few extra lines that the author can add in an afternoon.

The short version

Read a CFD report in five steps: the question it answers, the inputs it was given, what it showed at the hood and across the room, the scenarios it covered, and what changed as a result. Then connect it to the site: the same design figures go on to the commissioning measurement, and the measured numbers come back to you.

If you already have a report, or a design stage and want to know whether modelling or air balancing is the right step for your kitchen, tell us the unit, the cooking line and whether the system is built yet. Every system is sized to the specific kitchen, so there is no fixed price, and we will come back with a clear, no-obligation quotation. Our CFD modelling and air balancing page explains how the two fit together. WhatsApp BC Air on 8989 2833 and we are on standby 24/7.

Related reading: when a CFD ventilation study is worth paying for · make-up air and air balancing · ventilation for open-concept and show kitchens