DIY 200-250 Ducting for inline range-hood advice

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#2058684 19-Jul-2018 10:17

Does anyone know which would give me a smoother rectangular curve in a type space

Rigiflex:

https://smooth-air.co.nz/images/stories/products/pdfs/2595.pdf

Un-insulated flex:

https://smooth-air.co.nz/images/stories/products/pdfs/2593.pdf

My plan is to use a reducer to go from 200 -> 250 duct then make a rectangular template 300 x 90, put that inside the tube and deform about 50cm of tube into a rectangular shape, then pull it through the gap, then once out the soffit change about 20cm length into a gradual curve again and attach that to a vent.

PS (In case you suggest the following)...

You can buy a 220x90 mm rectanguar duct with adapter to 150mm, the problem is I can't get this into position, so it's not an option.

^ to get this device into position it would need to fit through a 150mm round hole in the soffit or a 350x100mm gap in the attic framing, which is not possible.

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nickb800

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#2058689 19-Jul-2018 10:25

The full flexible ducting has steel spring wire, so will spring back to ciruclar shape after you try to form it with your rectangular template. The semi-rigid duct probably would retain the rectangular shape, but it would be incredibly difficult to achieve without making a complete hash - crushing or tearing the tube. You would certainly need extra for practice!

I think you are going to have to accept reduced airflow or cutting large holes in the interior ceiling and soffit. Are you sure that the smooth-air adapter DPab229 wouldn't fit? Even if you have to go down in ducting size, say 60x204, the PVC duct has a smooth surface so air will flow more easily than a flexible duct of equivalent cross-section.

nickb800

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#2058694 19-Jul-2018 10:28

Presumably that adapter would fit on the rangehood end, just not the soffit end? What if you used something like the Smooth Air VE8282 on the soffit end, and had a rectangular outlet instead of converting it to a normal circular outlet?

nickb800

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#2058696 19-Jul-2018 10:29

Or if you're really stuck, do something yucky like chop one of those adapters in half to get it through the narrow gap, and tape it back together with aluminium foil tape.

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#2058697 19-Jul-2018 10:30

is there a external vent that can attach directly to 220x90 pvc duct?

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#2058698 19-Jul-2018 10:31

nickb800:

Or if you're really stuck, do something yucky like chop one of those adapters in half to get it through the narrow gap, and tape it back together with aluminium foil tape.

not a bad idea.

I get what you are saying actually if the flexible duct surface through the deformed part isn't nice and smooth even if the cross sectional area is larger the flow will be buggered.

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#2058702 19-Jul-2018 10:43

kiwijunglist:

is there a external vent that can attach directly to 220x90 pvc duct?

Sounds like the external vent is the least of your worries lol

But seriously, I can't see anything from Smooth Air or Simx, but I bet if you went into their stores you could find something that would be a close enough match that you could bridge the gap with aluminium foil tape.

rkl

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#2597195 3-Nov-2020 18:04

Holy thread revival batman!
I'm in the same boat, need to run 200mm duct to a soffit it little access.
What did you end up doing?
Anyone in this thread put a duct through a concrete tile roof, im pretty handy DIY, just unsure with how steep the roof is.

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#2597205 3-Nov-2020 18:20

I did it all myself.

I rounded the edge of the 4x2 slightly in the narrow gap. I compressed the ducting so it was a tiny bit oval / rectangular shape where it passed through the narrow area. The metal spiral was able to hold the shape. I did gradual transition in the shape of the tube.

I exited out the soffit

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MikeAqua

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#2597433 4-Nov-2020 10:00

kiwijunglist: I did it all myself.

I rounded the edge of the 4x2 slightly in the narrow gap. I compressed the ducting so it was a tiny bit oval / rectangular shape where it passed through the narrow area. The metal spiral was able to hold the shape. I did gradual transition in the shape of the tube.

I exited out the soffit

How have you found the performance of the extractor?

Mike

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#2597757 4-Nov-2020 17:34

Very good

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#2597887 4-Nov-2020 22:04

You could have also split it into 2x150mm and had two vents?

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#2597974 5-Nov-2020 06:33

Yup that's what I almost did but when I rounded off the edge of the 4x2 above and below it was squeezing through it gave another 3-4cm and I decided to just leave it at 200mm with a slight squeeze.

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rkl

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#2598034 5-Nov-2020 08:11

Sweet thanks, might get back in there and see if I can do the same. Have got some guys coming out to quote to install the whole system through the roof. Might not be too much more to do that. Looking at $2-300 in parts alone for all the ducting, etc

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#2598157 5-Nov-2020 10:25

$300 sounds like heaps. Duct should be $50-100 and vent should be $25-50.

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