Smoke coming back into the kitchen: why the chimney is not taking it out

The chimney is on, you can hear it, and the smoke drifts sideways and up into your face anyway. There are a handful of reasons, and one of them is not the chimney's fault at all.

The duct is blocked or crushed

Most common. A flexible duct kinks behind a cabinet, a bird builds in the outlet, or years of grease narrow the pipe. The fan pushes, the air has nowhere to go, and it comes back the easy way — into the room.

The outlet flap is stuck

The cowl or flap at the outside end should swing open when the fan runs. Grease glues them shut. From outside you can often see it not moving.

Backdraught from wind

If the outlet faces the prevailing wind, a gusty day pushes air back down the duct faster than the fan pushes it out. A different cowl usually solves it.

The kitchen is sealed

A chimney can only push air out if air can come in. A tightly closed kitchen with the door shut starves it. Crack a window and see if the smoke behaves.

The fan is too weak

Filters clogged, blades greased, or a motor that has lost its strength. If the chimney is also quieter or slower to spin up than it used to be, this is it.

Try the window test first. If opening it fixes the smoke, the chimney is fine and the room needs an inlet. If not, the duct is the next suspect, and that needs someone on a ladder.