Very looo...oong extractor ducting. Is this feasible?

Discussion in 'Plumbers' Talk' started by Theo70695, Sep 13, 2017.

  1. Theo70695

    Theo70695 Member

    I live in a grade II listed building and have been granted permission to covert a small bedromm in the front of the house to a shower room. In applying for the listing I neglected to specify an extractor outlet. I would hate to go through the application process again to get permission to install a grating on the front of the house. It would probably not be granted. So the idea is as follows:

    1. Fit an inline centrifugal fan couped to a ceiling vent above the shower.
    2. Take the exhaust through about 10m of ducting to a Y piece to couple with the bathroom extractor exhaust.

    Points to consider.

    1. Ducting resistance. Would it be crazy to expect a useful flow through this distance? Should I fit a reducer to, say increase the X sectional area to twice that of the 120mm outlet?
    2. Condensation. I would need to duct vertically for about 1.5m above the fan outlet and then elbow to run on what I would hope would be a gradual fall to the Y piece Am I likely to avoid the condensation problem by wrapping and tapping a good thickness of roofing insulation around the duct for its whole length?

    I have no experience of fitting extractors so I will be grateful for any advice.

  2. Pollowick

    Pollowick Well-Known Member

    I would suggest you might need an extra fan in line after the Y-junction. It will need to come on whenever one or both of the others are in use. And put some in-line one way flaps to stop the shower room extract being diverted to the bathroom and the other way too
  3. Tricky Dicky

    Tricky Dicky Active Member

    Also keep corrugated flexi pipework to a minimum, use smooth walled 100/110mm etc pipe or ducting to keep air resistance to a minimum.
  4. Devil's Advocate

    Devil's Advocate Well-Known Member

    Hi Theo.

    Lot's of potential issues with your plan.

    Air will find the paths of least resistance, and will divide in proportion to the resistance of the various paths available to it. So expect some of the ventilated air from your new shower to come out in to the other bathroom. And possibly even a little bit the other way too - enough perhaps for, er, smells to trickle out in to the new shower suite...

    Pollo's idea of an additional fan on the final leg of the ducting before it exits the building is a good one in theory. It would almost certainly work, I think, but then you'd have to figure out how to wire it up - the ideal scenario would be to have it coming on when either of the other fans are running, but that will need complex (or extra-pole) fan switches. Or, you simply have a 2-way switching so that all THREE fans come on every time one is triggered!

    Where does the existing fan exit? Any chance of widening that exit point and adding a second grill so's you can keep both separate? That has to be the best solution.

    As for the distance, it's all possible, but just needs more powerful fans - or even two.

    For the potential condensation issue, yes adding insulation to that vertical section should help, but won't eliminate the problem. I think your best solution is to use a timer fan and have it running for as long as is necessary after use - 5 minutes min, I guess - to ensure that the ducting is effectively 'blow-dried' after each use :)

    On this point, if the noise will cause a problem in the rooms below, consider siting the actual fan in a further away location, and you can even fully-suspend these in-line fans on strong cords to prevent contact vibration.
    PhilSo likes this.
  5. kiaora

    kiaora Active Member

    How about a unit in the roof void? Even a heat recovery unit?
    This can possibly accommodate the whole house?


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