Hood Losing Suction? Airflow Is Usually the Key

A hood only moves as much air as the whole path allows: filter, fan, duct and the outdoor termination. The hood manuals for La Cornue put the weight on the duct. The Chateau motorized hood guide says duct design is the biggest factor in performance, and that more than two 90-degree bends significantly degrades extraction. It specifies metal ducting only. The CornuFe hood guide says no duct section should be smaller than the hood’s collar, runs should be short and direct with few elbows, and rigid metal is the only duct it recommends; flex duct is not.

These are installation facts, which is why a hood that has lost suction over time and one that never had good suction are two different problems. The first often responds to cleaning. The second usually does not.

Because grease collects on the filters and fan, the CornuFe guide tells owners to clean them frequently so buildup does not form. Baffle filters can go in the dishwasher with the detergent inlet holes facing up, and must be completely dry before they go back in. On the Chateau hood, the controller flashes all six indicators after 30 hours of running to signal grease-filter cleaning, and the guide gives dishwasher or hot detergent water every 2 months or sooner. If your hood recirculates, the HP4 carbon filters are consumables and are not a washable fix once they are spent.

Check also that the filters are seated fully. A filter left slightly out of position lets air bypass it and changes the sound as well as the pull.

For the CornuFe 390 CFM models, the guide says the duct run should not exceed 20 linear feet with two 90-degree elbows. Each 90-degree elbow counts as 8 feet and each 45-degree elbow as 4 feet. It also says ducts must not be arranged so that exhaust flows downward. You can use this to compare your layout with the manual, but have the measurement done by whoever installed or maintains the duct, since reaching it often means working in a ceiling or wall.

Room pressure matters too. The Chateau guide notes that strong extraction can create negative pressure that affects fuel-burning appliances, cites a 4 Pa limit, and advises providing make-up air or not running both together if in doubt. A kitchen that is sealed tight can make a hood feel weak and also interferes with burners, so a nearby window opened slightly during a test is a sensible check on a day you are cooking. If the pull improves, tell your installer.

Cooking style changes how quickly the problem returns. Frying, searing and wok cooking load the filter faster than simmering, and the manuals advise running the hood for high heat or flambe cooking. Running the hood whenever the burners are on high keeps grease from settling on the filters.

If cleaning the filters restores the pull, the filters were the cause and a calendar reminder will keep it that way. If it does not, the duct, make-up air or the fan itself is the next candidate. A rattle with weak extraction fits the duct explanation in the manual, while a hood that is quiet and weak could have a restriction near the outlet. None of this tells you exactly which part is at fault, and a measurement is what settles it.

Remote and display behavior is a separate matter. For the Chateau hood, if the remote does not respond, the guide lists checking power, the latching red reset switch behind the grease filter, the battery, and re-registering the remote within the 15-second start sequence. The hood also shuts off by itself after 4 hours without operator action, which can look like lost suction during a long cook.

Stop if the hood loses power entirely, smells hot or electrical, or a breaker trips. Do not open the housing or reach into the motor area, and note that the built-in LEDs on the Chateau hood are not user-replaceable. If you also notice that burners behave oddly when the hood runs, such as flames that lean or extinguish, treat it as a ventilation problem with gas appliances. The CornuFe range guide warns that systems directing air downward at the range can cause ignition and combustion problems. Record the hood model, the speed where the problem appears, when you last cleaned the filters and any indicators that were lit.

Why is my new hood weak?

The manuals identify the duct as the main factor: size, length, bends and material. Compare the installation to the guide.

Can I use flexible duct to fix a tight spot?

The CornuFe guide does not recommend flex duct and calls for rigid metal.

How do I reset the filter reminder?

On the Chateau hood, the guide says to reset it with RUN ON TIMER after cleaning the filters.

Should I open a window while cooking?

The Chateau guide advises make-up air where strong extraction could affect fuel-burning appliances. Ask your installer what suits your kitchen.

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Official manuals and support notes are available on La Cornue Support.