Ventilation ducting for kitchen

[Jon R Smith]

Is it more efficient to use round or rectangular ducting?

[Ralph]

For a given cross sectional area of duct, the circumference of the circular duct will be less than a rectangular duct, meaning there will be less drag as the air moves through the duct if it's circular. So you could use a smaller fan but the difference is likely to be quite small. Your choice is more likely to be driven by what size and shape holes you've got available for routing the duct.

[landie]

Depends whether or not the the diameter of the round duct is the same as across flats, or across corners, of the square. If it's across corners it will be bigger than the square and capable of moving more air. It may also be flexible, something you rarely get with square ducting.

What shape is the hole in your wall?

[landie]

Sorry Ralph, I mis-read your answer, you are quite correct. My apologies.

regards

[Tim Baxter]

Don't forget that because there is more drag in the box section then, grease and dust will build up more quickly where eddies occur thus making the circular section cleaner for longer.