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I am looking for a extractor hood, and I see that there exist ones with air recirculation, so a pipe to lead the smoke/greasy air away is not needed.

So I wonder, how good are these?

Can they really clean the smoke/greasy air they pull in?

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I had one once. Utterly worthless. All they do is filter out large grease particles. The day you burn something on the stove is the day you'll wish you had an exhaust fan. – Carey Gregory Jan 14 '12 at 23:19

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If you have a gas stove, you need a hood to send the exhaust outside. One that recirculates is not sufficient.

In my experience, the recirculator hoods work OK if you're not doing a lot of cooking. If you do, however, you'll end up with a nasty, greasy dusty coating on everything in your kitchen. I wouldn't bother with a recirculation hood if you ever cook things that involve grease or smoke. For someone who mostly heats up processed foods, it's probably good enough.

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You hit spot on. It is a gas stove I have =) – Sandra Schlichting Jan 14 '12 at 22:21
Here, in Poland, it is perfectly normal to have a gas stove (very, if not the most, popular here) and no hood with external exhaust. In fact it may be impossible to legally install such hood in our kitchens. – Jacek Konieczny Jan 15 '12 at 20:21
Speaking as someone with a gas stove and no exhaust duct (apartment), Adam is absolutely correct. Anything we store high-up in the kitchen has to be cleaned with Goo Gone once a year. – FuzzyChef Jan 15 '12 at 22:44
With gas, not only do you have the grease, smoke, steam, and odors from cooking, you also have the combustion products of your stove. Depending on how cleanly your stove burns, there may be significant levels of carbon monoxide. Even if there aren't, your stove is still putting out significant amounts of carbon dioxide, so you want fresh air coming in to replace it. – Adam Jaskiewicz Jan 15 '12 at 23:41
This is all true, but in the case where the choice is: recirculating vs nothing at all, from experience, recirculating is better. – yossarian♦ Mar 25 at 20:48
up vote 3 down vote

Burning gas produces noxious gases such as carbon monoxide and nitrogen dioxide that recirculating hoods do not remove.

Ducted hoods can be made quieter by locating the extractor fan at the far end of the ducting, away from the kitchen.

Recirculating hoods require regular replacement of their carbon filters, meaning expense. Ducted hoods don't have or require filters.

Because of the carbon filters in recirculating hoods they can not achieve the airflow ducted hoods can for equivalent motor sizes. If you're doing lots of frying or high heat wok cooking, your hood must be sufficiently capable or you will just get a horrible nasty grease film EVERYWHERE. This is indeed a fire hazard with under-spec'd extraction often being the cause of Chinese restaurants burning down.

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To all the people who have already commented, Please, please, please do not comment unless you actually understand what you are saying. Two people have stated that CO gas can be produced and while this is true, as a gas it is heavier than air and will sink in a room, so any type of extractor will not help at all. To the person who said nitrogen dioxide can be produced, you are simply wrong. This can be produced in CAR engine combustion due to the high pressures and temperatures or in lightning strikes, it is never produced in cookers. It is very misleading if people write incorrect information – Alf Mar 25 at 18:37
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@Alf Well, CO is (a) about the same density of air, it takes a while to settle, and only if the room is still; (b) is actually lighter than air at both NTP and STP; (c) the CO is also hot, further lowering density; (d) there is an air current pulling gases (all of them) up and out. Maybe you looked up CO₂ instead of CO by mistake? – derobert Mar 25 at 21:27
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@Alf: From epa.gov/iaq/no2.html: The two most prevalent oxides of nitrogen are nitrogen dioxide (NO2) and nitric oxide (NO). Both are toxic gases with NO2 being a highly reactive oxidant and corrosive. The primary sources indoors are combustion processes, such as unvented combustion appliances, e.g. gas stoves, vented appliances with defective installations, welding, and tobacco smoke. – cookie Apr 9 at 8:59
up vote 2 down vote

In some kitchens external exhaust just cannot be done e.g. a flat in a block of flats, with shared ventilation shaft. In such case the choice is: recirculation hood or no hood at all. In such case the former may be better that nothing, as it catches at least a bit of the unwanted particles and odors, provided the filters are regularly replaced.

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