cooker hood queries (condensation trap, draft shutter)

[seneca]

not sure this is the right forum, but I have a couple of queries.

I want to vent a cooker hood with 150mm duct (70cm high), converting to 220 flat at a 90 bend, then 1m of flat and another 90 bend to outside. I have a powerful hood (650 m3) so it should be able to cope.

queries -
The manual says I should include a condensation trap and i presume this is on the vertical 150mm pipe. Trouble is, I can't find one at this size. They tend to be 100mm, and I would rather not reduce the ducting size. Also, am I right in thinking the trap would need an outlet? There is a stainless steel chimney around the ducting, so where is the outlet meant to go to?

The 220 flat that goes out through an airbrick only has a the dampning louvre design so no back draft shutter. If I were to install one, it would have to be in the ducting somewhere. Should it be nearer the hood's fan, or nearer the wall outlet?

Incidentally, why are the airbrick outlets available in single, or with an adapter to make it into a double? In the double only the top half is used.

 

[dextrous]

Am not really convinced that for that length of ducting a trap will be necessary. My understadning of these is that they are designed to trap condensed fats which may want to fall back onto the hob over time and become a potential fire hazard. For a domestic situation, having access to the ductwork (through dismantling) once in a blue moon would be sufficient to wipe the grease that has got through the paper grease filter within the hood itself.

The (warm) airflow is likely to keep water moisture to a minimum, but it you are worried, then creating a slight fall over the "horizontal" section of the flat ductwork away from the hood should allay your fears.

As for the back-draught, since the grease filter within the hood remains in place, (the charoal one being removed as you're not recycling the air within the kitchen) this will act as a draught excluder in its own right, but a vent flap with a flyscreen would be advisable.

 

[seneca]

thanks for the response. The kit I have got has an single airbrick that fits on to the end of the flat channel. It's the kind that has damping sloped lines on the front, no flyscreen. I might see if i can get the same thing with a flyscreen. Only problem with a flyscreen is it might become clogged up by the extracted air. I have read somewhere that it is useful to have the airbrick sticking out from the wall instead of being flush against it. Something to do with the grease and fats staining the wall. Anything in that?

Any idea why there is an adaptor for a double airbrick, even though only half is used?

 

[dextrous]

Only problem with a flyscreen is it might become clogged up by the extracted air. I have read somewhere that it is useful to have the airbrick sticking out from the wall instead of being flush against it. Something to do with the grease and fats staining the wall. Anything in that?

Think that's more for heavy usage than anything - the grease filter in the extractor (am obviously assuming certain things about the type you've got) will capture most solid bits that might block up the flyscreen anyway. Thinky you're making a bit of a mountain out of a molehill here if you don't mind me saying - no offence, but stop worrying so much.

Any idea why there is an adaptor for a double airbrick, even though only half is used?

It may be that an original hole was for a circular vent and that you need a double plate to cover it for aesthetic purposes. As for only half of the area being used, I suppose this is because the channel vent pipe will only cover half of it anyway, so the other half is obsolete.

 

[seneca]

Thinky you're making a bit of a mountain out of a molehill here if you don't mind me saying - no offence, but stop worrying so much.

point taken. Just want to make sure I'm getting it right, as I really don't want to have to take everything apart to re-do at a later date. Most of my "concerns" were based on not having a decent set of instructions to follow. Having spent over 500 on the hood, I'm a bit disappointed with the installation instructions - one sheet of A4. Not so much worried, as lazy! (with the fear of being endlesly nagged if there is a problem afterwards.)

thanks again for your help.

 

[dextrous]

Thinky you're making a bit of a mountain out of a molehill here if you don't mind me saying - no offence, but stop worrying so much.

point taken. Just want to make sure I'm getting it right, as I really don't want to have to take everything apart to re-do at a later date. Most of my "concerns" were based on not having a decent set of instructions to follow. Having spent over 500 on the hood, I'm a bit disappointed with the installation instructions - one sheet of A4. Not so much worried, as lazy! (with the fear of being endlesly nagged if there is a problem afterwards.)

thanks again for your help.

It amazes me the price of these things - basically a simple fan with a few speed settings, a light and a bit of shapes metal and maybe a piece of safety glass. But I guess that's life.

 

[seneca]

what can i say? when you boil it down you're completely right, but then "those" designing the kitchen know best. Anything for a quiet life sometimes. At least I'm saving something by doing it myself. small victories