Cooker hood flaps?

[thewarlock]

Fitting a new kitchen, bought a new cooker hood. On the outlet on top of the unit, there's a 150mm dia exhaust, which has a pair of hinged flaps, presumable to stop a draught coming back jn.





But, when I put the flexible ducting on top, there isn't clearance for them to open their full 90 degrees, or really very far at all



I imagine this will dramatically reduce the amount of air the fan can shift, and probably won't be very good for it either.

Should I just remove them? The outlet isn't just going through an external wall, it's going through an old external wall, into a void space in the garage where it'll turn 90 degrees and attach to a pipe that runs about 2m, and vents out the front of the house in a fairly sheltered place.

I've seen 150mm straight pieces, ~60mm long that might sort the problem, but I'm quite tight on space between the top of the hood and the hole through the wall, so not sure that'll work.
Anyone got any ideas? Ran into a similar problem?

Cheers

[Vtekkers]

Stretch out the pipe, it might be because of the corrugations in the flue while compressed in the way for it to open

[jfdi]

If you can, avoid using the flexible pipe. Solid pipe as big and as straight as possible will make a big difference to the performance.

[Simpo Two]

jfdi said:

If you can, avoid using the flexible pipe. Solid pipe as big and as straight as possible will make a big difference to the performance.

This. I used 150mm diameter duct all the way - up, 90 degree bend then out.

[thewarlock]

Thanks all, I'll take it all onboard. For £3, I'll grab a 150mm 60mm straight piece and see if I can make it fit to solve this problem, I see what you're saying about stretching it out but I'm worried if the length is use isn't tight, it'll slump and stop them from opening.

It supposedly shifts 780 cubes/hour so I'm not too concerned about poor smoke clearing performance, but I'll see what I can manage in terms of solid pipe through the wall and connecting on the garage side.

For daft reasons the hole through the wall is at a downwards angle, so I doubt I'll be able to make the whole run from solid pipe, but I'll bear it in mind when I get to it at the weekend.

Thanks again.

[Simpo Two]

thewarlock said:

Thanks all, I'll take it all onboard. For £3, I'll grab a 150mm 60mm straight piece and see if I can make it fit to solve this problem, I see what you're saying about stretching it out but I'm worried if the length is use isn't tight, it'll slump and stop them from opening.

All the more reason to use ducting if at all possible.

thewarlock said:

For daft reasons the hole through the wall is at a downwards angle, so I doubt I'll be able to make the whole run from solid pipe, but I'll bear it in mind when I get to it at the weekend.

45 degree angles might help: https://www.amazon.co.uk/Fantronix-Degree-Elbow-Co...

Better still, set about the angled hole with a large power tool until it's horizontal

[Crumpet]

I didn’t have the space on mine to have an initial straight run, so had to use the flexi pipe like you have to make an immediate 90 bend.

As a result I had the same issue with the flaps being obstructed. I managed to get the pipe straight enough that they worked properly but then after a few days the pipe must have moved a bit and obstructed it, so out they came!

I bought some upgraded external vents that have decent sealing flaps on them and, to be honest, it’s fine. I think ideally try and get the flaps on the extractor to work, but removing them and adding some flaps further down the line also works.

Also worth noting that it’s significantly quieter without the flaps!

[thewarlock]

You never get closure on threads like this, so thought I'd post a couple of pics.

Was a faff, but was worth it!

Thanks for the advice