Cooker Hood ducting upgrade

[JamieH]

My current cooker hood ducting consists of white PVC hose connected to the hood's 120mm adaptor by tape. It travels up through a hole in the kitchen ceiling to the loft where it travels 1.8m horizontally along the loft insulation before turning 90 degrees downward to a hole in the loft floor/outside ceiling and a standard grille.

Although it's lasted for 15 years, I gather that rigid piping makes for a greater flow and reduced air resistance.

I intend to use 2 metres of 125mm rigid ducting and a couple of 90 degree round bends.
That covers the ducting travelling through the loft but what's recommended/best for the area from the ceiling hole above the cooker hood straight down 40-50cm to the 120mm adaptor?
Is a type of flexible aluminium ducting recommended for the final run?

Also, is it OK to use 3m foil duct tape on the 90 degree round bends in the loft or a specific type of sealant?

Finally, how would the 'final run' be connected to the round bend situated 40-50cm above the appliance?

Thanks in advance.

 

[JamieH]

Any suggestions would be much appreciated.

 

[cdbe]

Plastic all the way, not sure many people tape the joints but when I did mine I used foil tape on the "home made" joints and was very happy with it.

 

[JamieH]

What's best to connect down to the plastic adaptor on top of the hood?
I'm wondering if a short run of flexible silver ducting might be best if it's easier to connect to the adaptor (with a Jubilee clip) than rigid piping would be.

 

[phatboy]

In the loft, don't forget some pipe clamps to support the pipe, or in very hot weather it may sag a bit.

I used Soudal Duct Sealant in the joints, but as you only have a short amount, some silicone should be fine, then foil tape over.

Allow the rigid pipe to come down through the ceiling and seal the gap around, and you only need about 50mm of gap between that rigid pipe and the cooker hood. I used a piece of plastic flexi-duct to connect them, but metal would also be fine. TBH a taut plastic bag all taped on would probably be fine!

You mention an adapter, some hoods are 6", so you may find you can remove the 5" reducer and then duct it all in 6", would be quieter that way....