Salt air and the hood blower

Of everything in a coastal kitchen, the extraction system is the part that ages fastest and complains least. It fails gradually, nothing burns, and the lights go on working. The kitchen simply takes twenty minutes to clear instead of five, and by the time anyone says so out loud the repair has grown.

There is a reliable early warning, and it is audible.

Why salt is worse than salt water

The intuition most people have is that salt corrodes metal because it is corrosive. That is not quite the mechanism, and the difference explains why an inland kitchen and a kitchen in 32080 behave so unlike each other.

Salt is hygroscopic. It absorbs water vapour out of the surrounding air and holds it. A film of airborne salt that has settled on a steel surface does not simply sit there; it keeps that surface wet at humidity levels where a clean surface would be bone dry. On the coast, the relevant number is not how often it rains. It is that the metal is damp far more of the time than it looks.

That is also why the marsh side of Anastasia Island is not obviously better off than the beach side. Beachfront gets salt dramatically, in weather. A house behind the dune line on the marsh gets it steadily, at lower concentration, on the prevailing breeze, without pause. For corrosion, steady wins.

Two failures that feed each other

A blower wheel spins at a few thousand rpm, inside a housing above a cooking surface, in that persistently damp air.

The first failure is the bearings. Lubricant degrades, moisture gets where it should not, and the bearing goes from smooth to rough. Roughness is audible long before it is significant, which is the whole point of this article.

The second is balance. Cooking grease condenses on the wheel, salt settles into the grease, and the deposit builds unevenly because airflow across a wheel is not uniform. A wheel that is even slightly out of balance vibrates.

Then the two combine. Vibration loads the bearings sideways and wears them faster. Worn bearings allow more play, which allows more vibration. The curve is not linear, and the last six months of it are much worse than the first three years.

Reading the noise

The useful thing about this failure is its order. On the coast, the hood gets loud before it gets weak.

• A new whine or growl, constant with speed. Bearings. Early. Cheap.
• A rumble or throb that rises and falls. Wheel imbalance, usually deposit. Often cleanable if caught here.
• Rattling on start-up that settles once it is up to speed. Mounting or a wheel that has loosened on its shaft.
• Will not start on low, catches on high. The motor is no longer producing enough starting torque to overcome the drag. This is late. A motor at this stage is a replacement, not a clean.
• Loud but the kitchen is not clearing, and it was always like that. Not a bearing problem at all. That is capture, ducting or make-up air, and replacing the blower will change nothing.

The last of those is worth separating out, because it is the one people most often spend money on wrongly.

What lives outdoors dies faster

If the hood is served by an in-line blower in the attic or a remote blower on the roof, the housing is in the outside air permanently — the same salt, none of the air conditioning, and far more temperature cycling. Those units fail on the identical mechanism, sooner, and out of earshot, so the first symptom is usually performance rather than noise.

Exterior dampers belong in the same category. The flap on the outside wall is the most exposed component in the system and the least inspected. Corroded open, it admits outside air and humidity to the kitchen whenever the fan is off — which is also how salt gets a route inward. Corroded shut, it chokes the hood completely. It is a cheap part in both cases.

What actually helps

Run the fan for a few minutes after cooking ends, so the housing dries in moving air rather than sitting damp. Wash and dry the baffle filters on a real schedule rather than when they look bad; a loaded filter forces more grease past it onto the wheel. Make sure the baffles are seated in their tracks, because one sitting proud short-circuits the capture area. And go outside once a year and look at the damper.

None of that stops the process. It slows it, and on this coast slowing it is the whole of the available strategy.