Kitchen cooker hood: recirculating or with long extraction duct?

[Harry Bloomfield]

Go for round, single lengths if at all possible, but if it must be rectangular could you get alloy to avoid rusting and or seal the joints with clear mastic? A sheet metal fabricator, could probably make longer sections, in the metal of your choice and for not much more than ready rolled. Would round work, if it were squished down a bit into an oval, then boxed in? Air ducting I have seen on commercial sites, comes in lengths of many metres - the type with a spiral seam all the way along.

The holes in airbricks are quite narrow, so will dramatically impede the air flow, so a bad idea. Use a panel which includes a gravity closing system, to prevent wind blowing in, but opens with air flow out. Mine works well, just a single circular flap, pivoted above the flap centre.

 

[jacoscar]

Go for round, single lengths if at all possible, but if it must be rectangular could you get alloy to avoid rusting and or seal the joints with clear mastic? A sheet metal fabricator, could probably make longer sections, in the metal of your choice and for not much more than ready rolled. Would round work, if it were squished down a bit into an oval, then boxed in? Air ducting I have seen on commercial sites, comes in lengths of many metres - the type with a spiral seam all the way along.

The holes in airbricks are quite narrow, so will dramatically impede the air flow, so a bad idea. Use a panel which includes a gravity closing system, to prevent wind blowing in, but opens with air flow out. Mine works well, just a single circular flap, pivoted above the flap centre.

I was looking at PVC ducting, rectangular in the kitchen (as with the current kitchen design I only have 7 cm between top of cabinets and ceiling), possibly rectangular in the utility room and then convert to circular before meeting the external wall, or convert to circular as soon as it enters the utility room

Another route I am considering now is going up into the ceiling void in the kitchen and then straight out horizontally (the ceiling void is higher than the external flat roof); that will dramatically reduce the run length
I have a scheme here, hopefully it’s clear (thanks to my phone’s LiDaR scanner)

 

[Harry Bloomfield]

Another route I am considering now is going up into the ceiling void in the kitchen and then straight out horizontally (the ceiling void is higher than the external flat roof); that will dramatically reduce the run length
I have a scheme here, hopefully it’s clear (thanks to my phone’s LiDaR scanner)

I have not been able to make much sense of the scan, but might you be able to mix and match between the two routes? Up into void, then bring it down gradually through the utility room ceiling, then through the wall?

 

[jacoscar]

I have not been able to make much sense of the scan, but might you be able to mix and match between the two routes? Up into void, then bring it down gradually through the utility room ceiling, then through the wall?

Basically if I go up into the ceiling void above the kitchen and then horizontally through the wall I'm already outside, just above the flat roof of the utility room

(In the picture I've drawn also the other route)

 

[Harry Bloomfield]

Basically if I go up into the ceiling void above the kitchen and then horizontally through the wall I'm already outside, just above the flat roof of the utility room

(In the picture I've drawn also the other route)

So, is there space to install an out on that wall, without disturbing the flashing of the flat roof - if so, that seems like your best plan.

 

[Deleted member 174758]

I am looking at 204mmx60mm rectangular ducting and they only come in 1m lenghts...

Find a different supplier. The first 204 x 60 supplier I Googled (Greenmill) do 1.5mm in 204 x 60mm. If you go to 220 x 90 you'll get 2m lengths. Lindab do semi flexible round duct in 63 and 75mm with a smooth internal bore in lengths of 5m

 

[jacoscar]

How do I connect pvc ducts together?

 

[Deleted member 174758]

I've seen them screwed together (pan head self tappers into pilot holes). Silicon caulk to seal

 

[jacoscar]

I have bought this wall outlet from TS

https://www.toolstation.com/search?q=82914

And I need to connect it to a round 150 mm pipe; however the diameter of the wall plate is a lot smaller than the pipe
Is it supposed to be like that?

 

[jacoscar]

Adding the second picture

 

[Deleted member 174758]

You can get wall outlets to directly fit onto flat rectangular ducting - just not from TS (I thought you were using flat rectangulat ducting). Always best to get the ductwork and the vent from the same manufacturer

 

[jacoscar]

You can get wall outlets to directly fit onto flat rectangular ducting - just not from TS (I thought you were using flat rectangulat ducting). Always best to get the ductwork and the vent from the same manufacturer

I am converting from rectangular to round ducting in the ceiling void as it’s easier to drill a round hole than a rectangular one (the external walls are render on blocks)

 

[Deleted member 174758]

You could always just make a collar from closed cell foam, like a Fossa Caulk Saver or similar, then silicone it in place. Even expanding foam (ideally the low expansion stuff) would work. Comprand would also do the job but is a bit pricy for a one off job like this

 

[jacoscar]

You could always just make a collar from closed cell foam, like a Fossa Caulk Saver or similar, then silicone it in place. Even expanding foam (ideally the low expansion stuff) would work. Comprand would also do the job but is a bit pricy for a one off job like this

I guess if I just seal the round section of pipe to the wall with expanding foam, then it doesn’t matter if the pipe and the outlet plate aren’t sealed between them

 

[jacoscar]

It looks like I’ll have to drill through the flashing despite my earlier conclusion
Is this a bad idea or can it be made watertight again once the pipe is in place?