Wolf cooker hoods in Mandarin that run but clear almost nothing

A ventilation hood is judged entirely by an outcome nobody can see. Air either leaves the house or it does not, and everything else about the appliance is in service of that. This is why hood complaints are so often misdiagnosed. The part that is easy to look at is the hood, and the part that is usually at fault is the duct.

We start every hood call the same way, by establishing where the air is supposed to go and then finding out whether it gets there.

Which duct this page is about

One clarification before any of the rest of it, because the word duct does a lot of work in a house. The duct on this page is the cooker hood’s own: a short run from the hood, through the ceiling or the wall, to a cap outside. That is the only ducting this shop opens.

It is not the heating and air-conditioning system, and it is not connected to it. We do not service furnaces, air handlers, heat pumps, air conditioners or the supply and return ducts that feed the rest of the house, and a hood that has stopped clearing the kitchen is never a reason to ring us about any of those. If that is the problem, an HVAC contractor is the trade, and we will say so.

Noise that arrived gradually

A blower that has become louder over a year or two is generally telling you about its bearings or about its balance. Bearings dry out and the note gets harsher. Balance changes when grease builds unevenly on the blower wheel, which happens far faster in a kitchen where the filters are cleaned rarely, and an unbalanced wheel produces a low rumble that rises and falls with speed.

Noise that arrived suddenly is a different story and usually means something is touching something. A loose damper flap, a screw that has backed out, a filter that is not seated. Those are quick, and worth mentioning as separate symptoms when you call, because sudden and gradual point at different repairs.

Pull that was never there

Here is the pattern we see most often in Mandarin, and it is a house pattern rather than an appliance pattern. Somebody put a serious range into a kitchen built in the 1970s or 1980s, and put a serious hood above it, and then connected that hood to whatever duct was already in the wall.

The old duct was sized for a modest builder hood. It may be too narrow. It may run a long way through the attic to reach a roof cap. It may take four or five turns to get there, and every turn costs air. It may terminate at a cap with a screen that is now completely closed with lint and grease. A blower rated to move a great deal of air will still spin, still sound powerful, and still move very little through a duct like that, and the owner will reasonably conclude that the hood is failing.

The other version is worse and more common than people expect. The hood was installed with no duct at all, simply venting into the cabinet above or back into the room through a grille. In that arrangement the hood cannot remove anything. It can only filter, badly, and everything else it collects comes back.

We will tell you which of these you have on the first visit, plainly, even when the answer is that the appliance is fine and the installation is not.

The damper

Between the hood and the duct there is usually a backdraft damper, a flap that opens when the blower runs and closes when it stops so that outside air does not come back down. It is a simple part in a hostile place, and in a coastal-humid climate the hinge stiffens and the flap gets tacky with condensed grease.

A damper stuck shut kills the hood’s output completely while everything sounds normal. A damper stuck open lets humid outside air down into the kitchen all summer, which people usually describe as a draught or a smell rather than as a hood fault.

Filters and what goes past them

Baffle filters work by making grease-laden air change direction sharply so the grease strikes metal and runs down. They do that well when they are clean and poorly when they are loaded. Everything that goes past them lands in the plenum above, on the blower wheel, and eventually in the duct.

Degreasing the filters is a household job and we will show you the interval that suits how you cook. Degreasing the plenum and the wheel is ours, and it is worth doing before you conclude that a quiet-sounding hood needs a new motor.

Lights and controls

Lamps and touch controls sit in the hottest, greasiest part of the kitchen and are the parts most often affected by moisture. Flickering lamps are usually a connection rather than a lamp. A control panel that responds intermittently is usually a ribbon connection that has taken on grease. Both are worth checking before anything larger is considered.