condensation inside kitchen extractor duct?

I am about to fit an extractor fan in the kitchen. It's a conventional Elica unit (with filters) and has an external fan. The duct goes up from the extractor, runs for 3 metres horizontally (between the joists, above the ceiling) and then out through an external wall into the fan unit (mounted outside). The duct will be the flexible sort (150mm) with fibre glass noise insulation round it.
I am worried that the duct will collect water and/or grease etc. Should I worry about this? What do people do about it? Is access to the duct important?
thanks for any advice ... Robert
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On 06/11/2012 09:17, RobertL wrote:

unit (with filters) and has an external fan. The duct goes up from the extractor, runs for 3 metres horizontally (between the joists, above the ceiling) and then out through an external wall into the fan unit (mounted outside). The duct will be the flexible sort (150mm) with fibre glass noise insulation round it.

I would consider using rigid ducting , round or rectangular. This will give you far less resistance and better airflow and if installed with a slope will allow any condensation to exit and not accumulate. If you want to reduce noise then you really need "heavy" insulation the more mass the better I doubt normal glassfibre will help much. You can buy specialised duct and pipe noise insulation material, it is not cheap but works very well . I used it on my internal soil pipes to good effect. Having the fan external however does make a far quieter system as far as the kitchen is concerned.
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On Nov 6, 9:17 am, RobertL wrote:

Don't use the flexible duct, it will collect grease. Use smooth wall duct or PVC soilpipe and slope it slightly yo the outside.
Owain
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Thanks very much for these comments. I'll change to gently sloping 150mm plastic pipe within the 185mm joist depth.
Robert
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