Why coastal hood blowers fail first

Every other motor in a kitchen lives in still, dry air. The hood blower does not. It runs a few hundred cubic feet a minute of whatever is in the room, and in a house a mile from the Atlantic that air carries salt.

Salt does not attack the motor windings directly. It attacks everything around them. It settles on the squirrel cage, where grease aerosol binds it into a crust. The crust is not even — it builds up thicker on one side than the other, and an unbalanced cage puts a side load on bearings that were specified for none.

What you hear, in order

1. A faint rumble at the lowest speed setting only. The bearing is starting to dry out and the imbalance is loading it.
2. A rattle when the blower spins down. The cage is out of true.
3. A rising whine at every speed. The bearing is now the problem, not the cage.
4. Nothing. The thermal cutout has opened, or the winding has.

Stage one is a cleaning job. Stage four is a motor.

Why the sequence matters more than the noise

Owners usually call at stage three, because that is when the sound becomes irritating. Stage one is the cheap stage and it is almost always ignored, partly because a rumble at the lowest speed setting sounds like the blower doing its job and partly because it goes away when you turn the fan up — which feels like evidence that nothing is wrong and is in fact the opposite.

The reason the rumble is worst at low speed is that an out-of-balance wheel passes through a resonance at low rpm and runs above it at high rpm. So the quietest setting is the one telling you the truth.

If the noise appeared over a week rather than over a year, the cause is more likely something that has come loose or a wheel that has picked up a lump of crust in one place, and that is a cleaning and re-seating job.

Why the internal hood does worse than the external one

An in-line or roof-mounted blower sits outside the conditioned envelope. It gets weather, but it also gets airflow that dries it. An internal blower sits in a warm cabinet where condensate forms every time the kitchen cools down. Warm, damp, salty and greasy is the full set.

What actually helps

Wash the baffle filters on a real schedule, not when they look bad — by the time they look bad the grease is already past them. Run the blower for a few minutes after cooking so the housing dries. And if the hood has a removable cage, have it pulled and cleaned before the rumble turns into a whine.

None of that stops corrosion on this coast. It buys years.

The ducting half of the problem

When a hood moves less air than it used to and the motor sounds perfectly healthy, stop looking at the motor.

Roof caps on this coast corrode, and their dampers stick. A damper that sticks shut is an airflow complaint. A damper that sticks part-open is a humidity and insect complaint, and it is the one that gets left until August. Both are cheap to fix and both get blamed on the blower.

Long horizontal runs with several elbows are common in the single-storey and villa-scale houses here, because the duct was routed once, decades ago, on the shortest path available at the time. Every elbow costs airflow, and a blower asked to make that up runs hotter for its whole life — which brings the bearing conversation forward by years.

What we check on a call

Airflow at the hood face, current draw at the motor, the state of the wheel, the condition of the harness terminals in the cabinet, and the damper at the termination. Those five together tell us whether you are buying a clean, a wheel, a motor, or a roof cap.

We would rather sell you the cheapest of those that actually fixes it, because on this coast we will be back for the next one either way.