Extractor cooker hood with no vent

keith969

Meepster wrote: »

I could go into a lot of detail here, but I haven't got the time, however a recirculating hood can actually be better at getting rid of smells and steam than one that is vented.

This is due to the fact that 99% of people don't use them properly in the first place and if it's not being used properly, recirculating hoods are usually working more efficiently.

This is simply not true. An extractor will remove all stuff while a filter does a half hearted job and eventually gets choked by fat.

Sandtree

keith969 wrote: »

This is simply not true. An extractor will remove all stuff while a filter does a half hearted job and eventually gets choked by fat.

The fat filter is way before the additional filters for recirculating hoods (fat filters are the same for vented and recirculating) so if your carbon filters are getting clogged with fat then your grease filters are no good.

no1catman

I'm in the opposite position of currently have an extractor fan that vents outside, but in order to have a working gas fire, I'll need to convert it.
Probably block up the hole with expanding foam.
At the previous house, gas cooker was a shared wall with next-door.

Unfortunately, gas fire was disconnected, because when the extractor fan was on at max. it drew in the fumes etc into the room rather than go up the chimney! No matter how much I protested about how unlikely it was to happen - have to accept reality - they are not going to change.

keith969

Sandtree wrote: »

The fat filter is way before the additional filters for recirculating hoods (fat filters are the same for vented and recirculating) so if your carbon filters are getting clogged with fat then your grease filters are no good.

Simple physics would tell you that an extractor, as opposed to a recirculating filter, will perform better and last longer. Filters have their place but - having had both - extractors still perform long after a filter gets clogged up.

ComicGeek

keith969 wrote: »

Simple physics would tell you that an extractor, as opposed to a recirculating filter, will perform better and last longer. Filters have their place but - having had both - extractors still perform long after a filter gets clogged up.

No - simple physics will tell you that a recirculating hood, without the additional air resistance of ducting and external grilles, will have a higher air flow rate than an extractor with the same fan motor. Simple physics will also tell you that as the filter gets clogged up the air resistance significantly increases, resulting in a significant reduction in air flow - neither system will work once the filter is blocked.

coffeehound

ComicGeek wrote: »

No - simple physics will tell you that a recirculating hood, without the additional air resistance of ducting and external grilles, will have a higher air flow rate than an extractor with the same fan motor.

Another problem is that with modern draught-proofed homes, there is often no provision for make-up air to enter the building, so an extractor simply can't extract at a useful rate. Opening a window in another room can help with that.

keith969

ComicGeek wrote: »

No - simple physics will tell you that a recirculating hood, without the additional air resistance of ducting and external grilles, will have a higher air flow rate than an extractor with the same fan motor. Simple physics will also tell you that as the filter gets clogged up the air resistance significantly increases, resulting in a significant reduction in air flow - neither system will work once the filter is blocked.

That's just sooo not true (and my background is physics btw) . Ducting and external grilles have a minuscule impact on airflow. And all the air goes out, unlike a filter which returns the (partially filtered) air to the room. I've had both - and my experience is that an externally vented hood works *far* better then a filter.

PasturesNew

Whatever responses you have received, or wanted to see, bear in mind: Extractor hoods are a fairly new thing and nobody had them a few decades ago.

The main thing is that when you cook you are confident that moisture/smells/whatever are sufficiently removed.... and so long as you're happy with what you see/smell an hour after you've cooked is "good enough" then that's sufficient.

Meepster

keith969 wrote: »

This is simply not true. An extractor will remove all stuff while a filter does a half hearted job and eventually gets choked by fat.

A vented cooker hood will "remove all the stuff", as long as the following criteria is met:

- The air flow of the hood is correct for the size of room (cubic m per hour)
- The ducting length is equal to or less than the maximum stated length (typically 5m, with a 25% reduction for every 90 deg bend)
- The correct diameter of venting is used (this varies from model to model, usually 100mm, 150mm or 200mm)
- The amount of air coming back into the room is equal to, or greater than what is being pushed out, to prevent negative pressure. This means opening an external window or door whilst the hood is in operation.
- The hood is positioned exactly the correct distance above the hob.
- The hood is switched on at least 10 minutes before cooking (and left on for 15-20 minutes afterwards too)
- The hood is set to the correct setting in relation to the amount of steam being released.

99% of the time, all these conditions aren't met, so no where near 100% of the "stuff" is being removed. The stuff being steam and odours - which also has a positive effect on humidity.

Whilst recirculating hoods aren't ever going to be 100% efficient, notice the point above in red; a recirculating hood doesn't need this, as the air isn't being lost from the room, whereas this has a HUGE effect on the efficiency of a vented hood. The majority of consumers don't know or understand this - believe me, I know from experience.

As someone else has already pointed out, the grease filter gets rid of the grease (fat). If the grease filter isn't cleaned or replaced often enough, the grease will clog up the filter. This can affect both types of hood.

And for the record I'm a kitchen designer, with a background in electronic and mechanical engineering.

grumbler

Bollo2019 wrote: »

So will filters be effective in extracting or will the steam, smells and grease not just bypass and end up being blown into the ceiling the hood is fixed to?

Don't know if some sophisticated filters exist (and cost arm and leg accordingly), but basic ones remove only grease. Not smell and definitely not steam.