Cooker Hood for Island - Where do I start ?

[cf-leeds]

Hi all,

I'm currently knocking through the kitchen to the dining room for a total kitchen conversion and will have an Island for the hobs and dishwasher.

Something that I thought was trivial has suddenly revealed itself as quite an in-depth topic.

I want to put in an extraction cooker hood above the island and planned to run a 150mm duct along the ceiling void, to the outer wall. At least a 4m run with one elbow, i.e. the elbow on the extractor - the rest can be a straight run.

Someone told me that a rule of thumb for a straight run is 3.5m assuming a straight tube (non flexi). I'm now having to research this, do I don't screw up and have an ineffective extraction unit.

So here are my quick questions, any answers appreciated:

1. Do hoods exist that have the fan motor on the outside wall, I assume this would be more effective and permit a longer duct length ? Worth looking at ?

1. Hoods without a duct, i.e. recycling hoods. Are they any good ? Can they stop a room streaming up ? Or are they to be avoided ? Do they have expensive proprietary consumables (special filters) ?

2. Any particular brands to consider or avoid ? I'm looking for performance here and not necessarily cheap.

Thanks for any input or sharing of experience. Sorry if this topic has been done to death previously, but I couldn't easily find the answers.

cf

[Bob Minchin]

There are extractors that fit in the counter top behind the hob and extract downwards and out under the floor which might be of interest?

[newshound]

Fan on outside wall would help reduce noise in the kitchen. I can't get worked up about the difference between 3.5 and 4 metres, particularly in

150 mm which is larger than the stuff used in normal domestic kitchens.

I certainly wouldn't bother with a recycling hood since you do have somewhere to send the moisture.

[FMurtz]

You can get axial fans that you can fit anywhere in the tube(more than one if you feel like it)

[tabbypurr]

kitchen conversion and will have an Island for the hobs and dishwasher.

e an in-depth topic.

o run a 150mm duct along the ceiling void, to the outer wall. At least a 4m run with one elbow, i.e. the elbow on the extractor - the rest can be a st raight run.

a straight tube (non flexi). I'm now having to research this, do I don't sc rew up and have an ineffective extraction unit.

his would be more effective and permit a longer duct length ? Worth looking at ?

ey stop a room streaming up ? Or are they to be avoided ? Do they have expe nsive proprietary consumables (special filters) ?

ce here and not necessarily cheap.

en done to death previously, but I couldn't easily find the answers.

If you want a fan on an outside wall you can mount an extractor fan there. But appreciate that axial fans have little ability to overcome duct resista nce compared to centrifugal. Inline extractor fans are also available. You can then have whatever you want as a hood, since it's only decorative.

Duct should be rigid where possible. Flexi causes a lot of air resistance.

Recirculating hoods don't extract anything. They're a way to pretend to hav e an extractor hood when you don't.

NT

[John Rumm]

Flow resistance will increase linearly with distance. So it stands to reason that if it works with a 3.5m duct, it will still work with a 4m one. However, flow rate will be reduced. Once could compensate for this with a more powerful blower, or by increasing the overall duct CSA - say running a pair of 100mm ducts. (having said that 150mm is fairly generous anyway)

Why do you assume this would be more effective? If you are attempting to move the same volume of air through the same obstruction, whether you push it or "pull" it does not really seem to matter (at least for the pressures and flow rates required for a cooker hood).

A separate motor however will allow you to select where the noise is generated.

(you also have the option of an inline fan - you could have one of these in addition to the one in the hood if you really wanted peak suck)

For some values of good. They normally have an activated charcoal filter and a dust / grease filter. So they reduce cooking smells and trap some of the oild / particulates that would otherwise end up coating the surfaces in the room. However they need more routine maintenance and filter replacements.

Not really - they have no way of actually getting rid of the moisture. They will allow some to soak into the filter, but that will become saturated and need to try out (putting the trapped moisture back into the room)

They are better than nothing, but not as effective as a proper extraction system.

They normally have cartridge filters in addition to the thin blanket style grease / particulate filters. These are more expensive and usually propitiatory.

Once slight gain however is on cold days you won't be venting heated air to the outside... how much of a benefit that is though is debatable since lack of heat is not usually something associated with a busy kitchen.

[cf-leeds]

Thanks for the responses. It's all useful info.

One idea I had is to use the native fan of the hood and have a second suction fan at the wall, powered on together with the hood fan. Worth a go maybe ?

[cf-leeds]

Actually - I see one of the responses already mentioned this (John)

"(you also have the option of an inline fan - you could have one of these in addition to the one in the hood if you really wanted peak suck)"

Thanks

[FMurtz]

That is what I said, (axial)

You can then have whatever you want as a hood, since it's only decorative.

[tabbypurr]

why do you think you need it? AIUI you've not yet used the thing to see if airflow is enough or not.

NT

[John Rumm]

While its an option, I doubt you would actually need it. I just mention it for completeness.

[harry]

Islands are a bad idea. There's a lot more effort inconvenience in walking round them. Just a wealth signalling icon.

[Harry Bloomfield]

[e-mail] presented the following explanation :

Correct, at best they might filter out some of the grease.