extractor fan ducting

[nospam]

Hello,

Is any one type of ducting better than any other (I'm thinking square, round, etc)?

Also, is flexible ducting worse than rigid ducting? I had to use some flexible ducting because of an inconveniently located concrete lintel, and I would think that having to deflect the air around a corner must slow it down.

I'd like to add a fan to our downstairs toilet. I need a decent length to get it outside. If I used the flexible ducting, even in a straight line, would there be turbulence because the edges are not as smooth as rigid tube? Should I use rigid tube wherever possible and just tape small lengths of flexible duct to it when I need to go around a corner?

Thanks.

[Andy Hall]

The rectangular stuff is a little worse than round because the sharper internal corners result in more turbulence in the duct. The surface areas may be smaller as well.

This depends on the ducting. Some has a fairly smooth internal surface.

It's better to make fairly gentle curves rather than sharp ones if you can.

That would be best if you can. Anothe approach is to use a larger duct size. Rather than 100mm that would be typical for a small fan, you could go up a size to 125mm for example.

You can use a more powerful fan and improve flow that way, but against a resistance, the fan will be noisier.

This can be compensated to some extent by using a good quality one such as a Vent Axia.

[djc]

Round is better than square, and rigid is better than flexible if flexible means that concertina type. For the best flow you want to minimise turbulence caused by sharp corners.

The Vent-Axia website has a very detailed document on the subject see