We're having our kitchen extended and the architect has noted (on our building plans) that we need an air extraction rate of 60 l/min. Question: Can this all be catered for just using a cooker hood (extraction to the outside), or does it need a 'higher up' fan?
On Mon, 23 Jan 2006 16:57:24 -0000 someone who may be "Grumps" wrote this:-
You may not think this a helpful reply, but that depends on the cooker hood.
Agreed, although I think your average cooker hood is designed to provide adequate ventilation to your average kitchen... it would be a bit of a mess to have a cooker hood slurping up 90% of the steam and fumes from the hob, only to have 10% sucked away across the room to the extractor fan on the opposite wall!
David
OK. Say the hood in question has an extraction rate >2 times what is specified by my architect. Is that going to be adequate, or is one still needed at ceiling height?
Yes.
Why do you think you need one at ceiling height?
With an oven under a hob the one extractor ought to be fine. But with an eye-level oven separate from the hob (IYSWIM) then any vapours or smoke coming out of the oven will not be so easily sucked out by the cooker hood.
Whatever you choose, I'd recommend installing a "damper" as per the BES web site
HTH
Mungo
Because my Draft 2006 copy of the building regs (section F1) says that mechanical extractors and fans should be preferably less than 400mm from ceiling height. Of course, the use of the word preferable must leave it open to interpretation. And there is also the question as to whether additional ventilation is required in the first place.
The cheap-as-chips bottom of the range hood I fitted a few weeks ago had one included within it, actually.
Dvaid
Be careful if you are using any length of ducting. Any significant length will annihilate the extraction rate, especially if it is an axial fan, rather than centrifugal. If it is straight through an external wall, then there is no problem.
Christian.
Thanks. It'll be a twin centrifugal fan unit, and straight through to the outside.
I hope you can turn it down!
Did you buy the optional wind tunnel attachment?
Christian.
:)
I thought the general consensus in this group was that two is better than one! Or am I talking drivel?
On Mon, 23 Jan 2006 16:57:24 -0000, a particular chimpanzee named "Grumps" randomly hit the keyboard and produced:
First, your plans should say, "60 l/second", not 60 l/min.
Second, a cooker hood capable of extracting at least 30 litres/sec will comply.
Yes, of course. They do! My typo.
Why is this?
It's in the regs. I believe it is because a cooker hood extracts from where the steam and fumes are generated, so is considered to have the same effectiveness as an extractor twice the size that might situated away from the cooker.
Christian.
Thanks. Sounds logical. I wonder why my architect didn't mention this. I don't suppose you know where abouts in the regs?
Part F.
Table 1.1a Extract ventilation rates
Kitchen 30 l/s (adjacent to hob); or 60 l/s (elsewhere) Utility room 30 l/s Bathroom 15 l/s Sanitary accommodation 6 l/s
Christian.
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