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Is it the hood, or is it the air that never comes back?
Two different problems produce most kitchen complaints, and they need opposite work. Tick what you see during service.
The check
Symptoms point; measurements decide. What settles it on site is airflow at the hood and the building pressure with the kitchen running — half a day with instruments. This runs in your browser and nothing is sent anywhere.
What this points at
Tick what you actually see during a busy service rather than what the building does when it is empty — the difference between the two is the whole subject.
These symptoms are what a building does when more air leaves than arrives. The extract is doing its job; nothing is replacing what it removes, so the building pulls air through doors, gaps and — dangerously — through flues.
- Measure the building pressure with the kitchen running and with it off. That single measurement usually settles it.
- Check whether a make-up air unit exists, whether it runs, and whether it is interlocked with the hood.
- Look at what has changed: a new extractor, a sealed-up louvre, a door propped shut, a tenant fit-out next door.
- Fix the supply side. A bigger extractor makes this worse, not better.
These point at capture and extract rather than building pressure: a hood that is not pulling what it should, ducting that has lost velocity, or a fan that is no longer doing its work.
- Measure the airflow at the hood and compare it with what the equipment beneath it needs.
- Check the fan, the belt if there is one, and the duct for grease build-up.
- Check the filters and how often they are actually cleaned — this is the cheapest thing on the list.
- Grease cleaning inside the duct is a specialist job and a fire matter; we will tell you when it is due rather than work around it.
A hood struggling to capture and a building short of make-up air produce the same complaints and amplify each other. Measuring both is the only way to know which to fix first.
- Measure hood airflow and building pressure in the same visit, with the kitchen running as it does in service.
- Expect the answer to be supply air first: a hood cannot pull what the room cannot give it.
- Then re-measure the hood. Some capture problems disappear once the pressure is right.
- Agree what is done during service and what needs a closed morning.
One thing that is never a comfort question: if gas appliances are blowing out, or if you smell exhaust in the kitchen, a flue may be back-drafting. That is a carbon monoxide risk and a same-day matter — ventilate, stop using the appliance and call, whatever the rest of this page says.
Four practical routes
- A make-up air unitTempered supply air interlocked with the hood. The proper answer where extraction is heavy, and the one that fixes the doors as well as the dining room.
- Rebalancing what existsSometimes the supply is there and switched off, throttled, or fighting an economiser. Cheap to find and cheaper to fix.
- Hood and duct workFan, belts, filters and duct condition — plus the cleaning schedule that keeps them working.
- Zoning the front of houseWhere the dining room suffers, separating it from the kitchen's air can be worth more than extra cooling.
