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Help Required Selecting a fan to be Ducted 2.5 Metres

Postby ThinkingFrowner » Tue Sep 17, 2019 3:13 pm

Hi there - I am hoping to find some useful help in choosing an extractor fan for my 'internal' bathroom (no windows and 2.5 metres from external wall). Since I moved in in April, there has been a distinct mustiness to the room. This has improved a little with a thorough deep clean and by running water through the sink and bath traps occasionally.

The bathroom is 11.5 cubic metres and I plan to duct the fan through the bathroom (plasterboard) wall and 2.5 metres horizontally (with no turns) through the kitchen and exiting via the kitchen exterior wall.

Unfortunately, there is no space under the floorboards above the bathroom for a more discreet ducted extraction.

Initially I planned to get an in-line fan, which would be sited on the kitchen ceiling. However, I would like to keep the fan noise within the bathroom (if possible), so I have been looking at centrifugal fans.

To this end, I would be really grateful if any of the diydoctor members could advise me on the following questions...:

1) Would you advise purchasing a fan with a trickle function to solve the mustiness aspect? (the vent axia solo plus and the envirovent EFHT2S have a trickle option - both are centrifugal fans)
Solo Plus: Trickle:32m3h, Max boost: 80m3h
Envirovent EFHT2S: Trickle:54m3h, Max boost: 216m3h

2) If I am to do without a trickle function on the fan, do you think a powerful wall fan with over run timer would be sufficient and still perform adequately with 2.5m of ducting? (such as a iCON60 - up to 260m3h)

3) Various professionals have informed me that, for 2.5m rigid ducting servicing a 11.5m3 room, resistance will be anywhere between negligible and 60Pa. Could anyone shed light on how Pascals for ventilation are calculated, and roughly what sort of extraction resistance I should expect?

4) Would an in-line fan be preferable, despite the noise and visual intrusion in the kitchen?

5) Could a trickle function result in condensation forming, necessitating the installation of a condensation trap?

I really would be most grateful for any help on any of this...!
Some tradesfolk have baulked at the job (assumingly because it involves a bit of wall drilling, electric work and tricky ducting and because it won't be beautiful, whichever way it's done!)
Many thanks for tking time to read this.
Kind regards,
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