Your hood is fine — the kitchen has nowhere to draw air from

A hood running flat out while smoke rolls along the ceiling looks exactly like a failing blower, and it very often is not one. Extraction is not something a hood does on its own. It is a trade: for every cubic foot of air the hood pushes outside, one cubic foot has to get back into the house from somewhere. If the house has nowhere to supply it from, the hood ends up fighting the building instead of the cooktop, and no amount of motor will win that argument.

This is the single most common misdiagnosis in kitchen ventilation, and it has become much more common as older housing gets tightened up. Test for it before you buy anything, because the test takes one minute.

The open-door test

Cook something that smokes — searing a pan is ideal. Shut the kitchen up: windows closed, interior doors as they normally are, hood on its highest speed. Watch what the smoke does.

Now open an exterior door or a window on the same floor, and watch again.

If the smoke visibly snaps up into the canopy the moment the door opens, your hood is mechanically fine. What was missing was air. The blower had built up enough negative pressure in a sealed kitchen that it could no longer move what it is rated to move, and giving the house a supply path handed it back.

If nothing changes when the door opens — same lazy pull, same smoke on the ceiling — then the problem really is on the hood side, and the next three checks are worth doing.

What actually fails on the hood itself

Loaded baffles. The most common genuine fault and the only one on this list you can fix in the sink. Baffles choke airflow long before they look dirty, and on a hood over a range that gets used most nights they want pulling and washing about monthly. They are dishwasher-safe on nearly every professional hood. Pull them, hold them up to the light, and if you cannot see clearly between the vanes they are overdue.

A crushed or over-elbowed duct. Every bend costs you, and flexible duct costs you far more than smooth rigid pipe of the same diameter. This is worth thinking about in older houses on the northwest side in particular, where a hood often has to reach an outside wall through a masonry chase and the duct takes two or three turns it was never supposed to take. A run installed with four elbows and a length of flex can deliver a fraction of what the hood is rated for while the blower spins perfectly happily.

A stuck damper. There is a backdraft damper somewhere in the run, usually at the wall or roof cap, and it is a flap on a hinge. Grease stiffens it and it stops opening fully. From inside the kitchen a half-open damper is indistinguishable from a tired blower — and from outside, with the hood running, it is obvious in about ten seconds.

The blower itself. Real, but the last thing to suspect rather than the first. A failing blower usually announces itself with noise or with a speed that no longer changes when you switch it: bearing rumble, a drumming vibration at top speed, or a motor that runs at one pace whatever the control says.

Lights are a different circuit entirely

One question that comes up alongside every hood complaint: a pair of lamps has gone dark while the other pair still works.

That is almost never the lamps, and swapping them proves it in a minute. Professional hoods commonly run their lighting in pairs off a transformer or a driver, so one dead pair points at that supply or at the switching, not at the bulbs. Halogen sockets also corrode in a greasy environment, and a socket that has gone high-resistance produces exactly the flicker people describe. Both are ordinary repairs, and neither has anything to do with why the kitchen is full of smoke.

What to do with the answer

If the open-door test transforms the problem, stop shopping for a blower. What you have is a supply-air question, and on a large professional hood the real answer is a dedicated make-up air path — building work, not appliance work. In the meantime, cracking a window on the same floor while you cook is a legitimate stopgap and it costs nothing to try.

If the test changes nothing, pull the baffles and wash them, then look at the damper from outside with the hood running. Those two account for most of what is left.

Everything after that — duct diagnosis, blower measurement under load, lighting circuits — needs somebody with a meter and access to the run. What is worth insisting on, from whoever you call, is that they do the supply-air test before quoting you a motor. It costs them a minute and it is the difference between a repair that works and a part that changes nothing.