Bathroom Extractor Ducting

Bathroom Extractor Ducting

1. Hi all,

   Recently I have noticed condensation falling back down through the extractor fan in my ensuite bathroom so went into the loft space to check it out.
   I noticed the ducting was not insulated which I know I need to sort out from reading other forums on here but also noticed there appears to be far more ducting than is necessary; as a result an awful lot of ducting is sat on top of the loft insulation and doubles back on itself etc. hindering airflow.
   I'd have thought, given hot air rises, the straightest, most direct route from the extractor fan to the external roof vent would be far more efficient and that the excessive ducting currently in the loft only means more pipe for the steam to condense in?
   Before I shorten the ducting myself to make the path from the fan to the exterior vent more direct I wanted to ask whether there is a valid building requirement for ducting to run horizontally across the loft space or is that simply lazy installation by the builders?

   Thanks in advance,
   James

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4. Instructions with some extractor fans will show you to loop the ducting so any condensation will collect in that bit. The only trouble is, I'm not aware of any kit on the market that does this with any drain valve built in. I've only had one customer that knew about this and we made a trap out of 4" waste fittings with a screw access cap so he could undo and remove any water build up..

5. Thanks for that. I am not in a position to build a trap in that I regularly need to empty; especially if there is not a plug and play model on the market. If I shortened the ducting and had it running straight up from the vent to the external roof vent / chimney then surely the water vapour would makes its way outside without giving the vapour time to condense?

6. You can wrap the duct in insulation, such as loft roll. It will then be warmer and get less condensation.

   Photos would be helpful.

7. Lazy builders. Ducts should be as short and straight as possible. The longer they are, the lower the performance of the extractor is.

   • Like x 4
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10. Yes, shorten it as much as you can, but also, make it going up rom the bathroom by as much as needed (foot should be plenty) so to have a slope down to outside.
    Also wrapping the duct in insulation will help.
    I have drained gallons of water from long ducts left resting on loft joists.
    Personally for longer ducts I prefer the rigid kind instead of the corrugated flexible ones.
    It's easier to make a slope and fix them permanently.

    • Thanks x 1

11. Where does the duct leave, in the eaves? Could you replace most of it with a tube? No idea if this is good practice, but my kitchen extractor (in bungalow) goes into roof with a short flexible duct, then runs to the wall in a solid waste tube, which is angled slightly downwards. It's not insulated though.

12. I will get some photos for you all but the chimney vents to the outside through the roof slates as opposed to running across to the soffit. There is approximately 3x metres of distance between the extractor fan and the external roof chimney / vent and the angle between the 2x points is approximately 45° upwards. Hope this description helps; I will try and sort photos today.

13. Short, taught, straight ducting is needed, minimum bends, no sags.

    Definitely needs to be insulated, you can buy pre insulated flexi or rigid ducting nowadays.
    Fan performance also needs to be considered along with back pressure when you have longer duct runs.

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Bathroom Extractor Ducting

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