Extractor hood

[John]

Just been admiring a friend's new kitchen. He commented the extractor wasn't very good and I suggested he gives some thought to how air is allowed to enter the kitchen to replace the air that is being taken out.

We got to thinking about why the fan is in the hood - and why isn't it on the outside at the end of the duct (he has quite a long duct - crossing the kitchen above the ceiling to get to the outside wall). I guess it makes things easy from a selling point of view to have everything in one unit - but we could see advantages in moving the source of noise to the outside.

Any thoughts or experiences of an external extractor fan?

[Andrew Gabriel]

It may be that the fan isn't suitable for a long pipe run. You can get hoods with powerful centrigugal fans designed for driving long pipe runs, but they're often significantly more expensive. It could also be that he has used too small a pipe for a long run.

That's normal for commercial grade kitchen extractors.

I built one for a shower room some years back. It was a 13" brick wall which already had a 3.5" old boiler flue pipe through the wall, so I built a waterproof extractor to go on the outside wall. The inside of the pipe is in the shower cubicle, and just has a grille. It saved trying to widen the existing hole, and there's nothing live in the shower cubicle.

did have a hunt around for an externally mounted extractor for this type of scenario, but was rather surprised to find nothing at the time. In the case of a kitchen hood extractor, the design would have to be different, as the fan I used here would clog with grease. They are usually centrifugal fans with the motor mounted out of the greasy airflow.

[Hugo Nebula]

On Sat, 3 Jan 2009 18:21:28 -0000, a certain chimpanzee, "John" randomly hit the keyboard and produced:

My completely un-scientific rule of thumb for a kitchen extract fan is that it should be able to hold up two sheets of A4 paper. Switch it on, then put a couple of sheets of paper under the grille. If it won't hold them, it's probably not powerful enough.

[JSM Distribution]

There are a few inline fans that we use that do a great job. Just fit a grill in a box unit above the hob at one end and a grill on the outside wall at the other.

Most hoods are manufactured as a compromise as not everyone wants to(or can) vent to an outside wall, so, for those who just want to put in a carbon filter, the motor stays in the body of the hood.

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