Restaurant Air Conditioning and Kitchen Ventilation

Extract and make-up air: the relationship that governs everything

A commercial kitchen extracts a large volume of air continuously to remove heat, steam, smoke and grease-laden vapour. That air has to be replaced. If it is not replaced deliberately, the building will find it — pulling air in through every gap, crack, door and flue it can.

The result is negative pressure, and its symptoms are unmistakable once you know what you are looking at: front doors that become heavy to pull open, whistling at door and window gaps, persistent cold draughts across the dining room whenever the kitchen is busy, and extract hoods that stop capturing properly because there is simply not enough air available for them to move. In the most serious cases it can affect the safe operation of open-flued combustion appliances, which is a safety matter rather than a comfort one.

The correct approach is to supply make-up air deliberately, in a controlled and — importantly — tempered way. Introducing large volumes of untreated outside air into a kitchen in January creates a different problem: a freezing kitchen and staff who block the supply grilles. Make-up air normally needs heating, and heat recovery from the extract stream is the sensible way to pay for that. Our ventilation and MVHR page covers the principles.

Balance is not a one-off calculation. It should be verified at commissioning with measured figures, and re-checked when anything changes — a new extract canopy, a blocked-off doorway, a re-fit of the front of house.

Grease, ductwork and fire risk

Kitchen extract air carries grease, which condenses and accumulates on the inside of ductwork. Over time this builds a combustible deposit along the full run of the duct, which is why kitchen extract cleaning is a fire-risk control rather than a housekeeping task.

The industry reference is TR19 Grease, published by BESA, which sets out how kitchen extract systems should be cleaned, to what standard, and how the result should be verified and recorded. Cleaning frequency depends on usage and cooking type — a high-volume operation with heavy frying needs far more frequent attention than a light-use kitchen.

Two practical consequences. First, insurers commonly require evidence of duct cleaning to a recognised standard, and a claim following a duct fire without that evidence is a difficult conversation. Second, systems must be designed to be cleanable — with adequate access panels along the full run. A duct with no access hatches cannot be properly cleaned, only certified as inaccessible, and that is a design failure that is expensive to correct later.

Grease also travels beyond the duct. It coats the extract fan, reducing performance, and it fouls anything on the roof near the discharge — including air conditioning condensers, which is a common and easily-missed cause of poor cooling performance in a restaurant. See AC servicing.

Gas interlocks and safety systems

Where a commercial kitchen uses gas appliances, the ventilation system and the gas supply must be interlocked, so that gas cannot be used unless the ventilation is running and proven. This prevents the accumulation of combustion products in a space where extract has failed or been switched off.

The interlock is a safety system and needs to be tested and maintained accordingly, with records kept. It is also a common cause of operational frustration — a kitchen where the gas has "stopped working" is frequently an interlock correctly doing its job because an extract fan has failed or an air-pressure switch has drifted. Understanding that saves a great deal of misdirected troubleshooting.

Front of house: comfort next to a heat source

The dining area has its own requirements and they conflict with the kitchen next door.

Heat migration from the kitchen is a constant load on the dining room, worst near the pass and any serving opening. Occupancy swings are extreme — an empty restaurant at 5pm and a full one at 8pm are very different loads, which again favours inverter plant that modulates well rather than fixed-speed equipment that cycles. Draughts matter more here than almost anywhere else, because a seated diner beneath a poorly-positioned diffuser will not return; terminal placement should be planned against the actual table layout rather than on a symmetrical grid. And noise from indoor units directly affects the atmosphere the operator is trying to create.

Where a venue has a cellar, that system runs continuously and is usually the largest single electrical load on site — covered separately on our cellar cooling page. Pubs and bars often need cellar cooling, kitchen extract and front-of-house comfort cooling considered as one problem, since they share plant space, roof area and electrical capacity.

Neighbours, noise and planning

Hospitality plant runs late, and hospitality premises frequently sit under or beside residential accommodation. That combination makes noise a leading cause of difficulty, including enforcement action.

The relevant assessment is BS 4142, comparing the plant's rating level with the existing background at the nearest noise-sensitive receptor — and background levels at 11pm are far lower than during the day, which is precisely when a restaurant's extract and condensers are working hardest. Assessing against daytime background is a common and expensive mistake.

Mitigation is available — attenuators on extract discharge, acoustic housings for condensers, careful siting, and anti-vibration mounting to stop structure-borne noise transmitting into flats above. All of it is markedly cheaper designed in than retrofitted after a complaint. Odour is the related issue: extract discharge position and height, and where necessary odour abatement, are commonly conditions of planning consent for a new restaurant.

Maintenance in a hospitality environment

Hospitality is among the most demanding environments for HVAC plant, and service intervals should reflect that. Grease fouls condensers and extract fans quickly. Kitchen extract duct cleaning runs to its own TR19 Grease schedule. Gas interlocks need periodic testing. Cellar cooling runs continuously and warrants quarterly attention. And front-of-house filters load faster than in an office.

Because a hospitality site typically has several distinct systems with different requirements, a single planned maintenance contract covering the whole site is usually more effective than separate arrangements — see maintenance and PPM and the SFG20 explainer. The usual compliance duties apply throughout: F-Gas on all refrigerant plant including cellar cooling, and TM44 where the site's air conditioning exceeds 12 kW, which in a restaurant with front-of-house cooling it very often does.

Frequently asked questions

Why is our restaurant front door so hard to open?

Almost certainly negative pressure caused by the kitchen extracting more air than is being supplied back into the building. The extract pulls replacement air in through every available gap, including the door. The fix is supplying tempered make-up air to balance the extract rate — adjusting the air conditioning will not solve it.

How often should kitchen extract ductwork be cleaned?

It depends on usage and cooking type — heavy frying and high volume need far more frequent cleaning than light use. The reference standard is TR19 Grease, published by BESA, which sets out the cleaning standard and how results should be verified and recorded. Insurers commonly require documented evidence of cleaning to a recognised standard.

Why does our air conditioning struggle even though it was fine when installed?

In a restaurant the most common cause is grease fouling the condenser, particularly where it sits on a roof near the kitchen extract discharge. A greased coil cannot reject heat properly, so the system runs longer and delivers less. It is a maintenance issue rather than a fault, and it needs a shorter service interval than an office would.

Our kitchen gas keeps cutting out — is the ventilation to blame?

Very likely, and it is the safety system working correctly. Gas appliances in a commercial kitchen are interlocked with the ventilation so gas cannot be used unless extract is running and proven. A failed extract fan or a drifted air-pressure switch will cut the gas, so the ventilation system is the place to look first.

Can our extract system cause problems with neighbours?

It is one of the most common sources of complaint and enforcement in hospitality, because plant runs late at night when background noise levels are much lower. Assessment under BS 4142 should use the night-time background, not the daytime figure. Odour from extract discharge is the related issue and is frequently a planning condition.

We work across hospitality — kitchen ventilation, front-of-house comfort cooling and cellar cooling — throughout the UK. See ventilation and heat recovery, servicing and TM44, and the sectors index for other building types. Or request a quote.