Extractor hood duct - to reduce or to elbow?

[Brad.BradShaw]

Hi All,

Lots of helpful discussion in previous threads, but my question is now specific.

Background: I have just redone my kitchen. In an effort to do all the dirty work up front I drilled the core hole for the extractor hood pre-plastering. 120mm straight (slight angle down) through two skins of brick, was going to use a solid duct through it for all the good reasons.

Problem: Some alterations to range cooker positioning occurred - which meant my lovely straight hole is now 25mm to the left of where it needs to be and I don't have enough play in the chimney enclosure to get away with it.

The question: Given the assumption that I am not trying to core another hole and mess up the outside brickwork, should I:
A) Reduce to 100mm, remaining straight
B) Knock out / drill out on the internal skin allowing an offset in either rigid or flexible but staying at 120mm

I know I will take a performance and noise level hit with either, but which will have less effect. I did try to calculate it myself, but I was struggling.

Thanks in advance.

Brad

 

[^woody^]

B

 

[Ian H]

A, with it being such a short run.

 

[JohnD]

C

Put the hood 25mm out of line with the cooker.

 

[bradshawjgc]

Thanks Chaps. Wonderfully conclusive!

I shall await a vote to sway. Anyone fancy pointing me at the maths to calculate the performance of A Vs B, albeit approximately?

Thanks

James

 

[^woody^]

There is no performance hit, nor noise increase.

This is what, a metre of duct from fan to terminal? You are worrying about nothing.

 

[Brad.BradShaw]

Thank you Woody.

 

[pilsbury]

Flexi hose?

 

[John D v2.0]

D change to recirculating



Just kidding, I'd go for B enlarging the hole and sticking with 5 inch pipe. As pilsbury suggests the "semiFlexi" hose is not a bad idea

 

[jasonzyx]

E, redesign the kitchen?