inline fan/ condensation trap/ ducting /botch job

Discussion in 'Electricians' Talk' started by bunhead, Nov 30, 2017.

  1. Sparkielev

    Sparkielev Well-Known Member

    D A is right the issue is with the T junction try turning around it may help, if it were me I'd add another fan and T into the straight duct going up
    bunhead likes this.
  2. bunhead

    bunhead Member

    Thank you Sparkielev...

    I actually have 2 pics where the old fan vent used to be. Its where right below where i put down a tape measure on the floor .

    I also show another full length picture for comparison. The pale vertical wood i leaned against the wall is where the old fan vent exit used to be, to the left of the main vertical plastic pipe.

    Attached Files:

  3. bunhead

    bunhead Member

    Sparkieliev... does my kitchen extractor hood/fan above the oven not count as a fan?
  4. Yes it does, but the issue is that the kitchen extractor 'pushes' the air along that pipe, so the air pressure is higher in that flow. Hence the air will try and find any way out before it finally reaches the external vent. And that bathroom vent is a good candidate.

    I know you can fit one-way 'flaps', but these are not air tight. They will stop strong gusts and air currents, but not 'seepage'...

    The idea of having the in-line fan as close to the exit vent as possible in a 'twin' situation like yours is that by having the fan 'sucking' the air out of that pipe it is now creating a lower pressure environment, so that will tend to draw air in to the pipe from every orifice.

    I really don't know if there's a perfect solution in your case, one that is guaranteed to work. The only proper solution is a second, separate external vent - is there no chance of this?

    The only other 'guaranteed' solution is to have that in-line fan wired to both the bathroom switch and the kitchen extractor so it comes on and draws from both whenever either is called on, but that's hardly practical, is it?

    Failing that, the best result will almost certainly be by taking each extractor vent - the kitchen and bathroom - via separate ducts as far as possible towards the ext vent and then join them using a 'Y' branch (which are available) as close to that ext vent as possible. You then hope that when the bathroom fan is on all the air will choose the easiest path - out that ext vent - and none will be forced all the way back down the long tube to the kitchen.

    But, as will water and leccy, some will always go the difficult paths too - it's all in proportion.
  5. bunhead

    bunhead Member

    This sounds as though i will be paying for something that has no guarantee that it will work unless i can get a second hole in the roof installed. I will ask the guy if he can do this but I am not hopeful

    The problem i live in a top floor flat (its a low rise flat on the 3rd floor.

    The price i got quoted to get the 2 separate ducts done that will exit out of the single exit are over 1k which is scary.

    I just didn’t know who to turn to as the two guys who did the job charged charged me 280 pounds but they did bad jobs.

    The old original system before i had ANY in-line fan worked. I was thinking, to save money ,to just have the old system reinstalled and to get a weak silent fan and let it run for half an hour

    D, A.... this is a long shot, but do you work in London at all?
  6. Not only do I not work in London, I don't work anywhere :)

    The original cost of £280 is probably fair enough for the work done, BUT they should have been clued up enough to not have done it in the first place as it wasn't likely to perform correctly. And, when it then did not work, they should have been either called back to sort it FOC or else sued for the return of the money.

    The one that allowed bathroom smells in to the kitchen could easily have been reported to the BCO - that SURELY contravenes regs.

    I would not consider handing over £1k for a second - even IF this came with a guarantee of working. That's crazy money.

    Can you describe - ideally with a pic - what the outlet vent in your roof looks like? I wonder if there's any way of 'splitting' it to allow two smaller pipes through? This would reduce flow, of course, but it certainly wouldn't be an issue for the current in-line fan as it's more than powerful enough to cope.

    The addition of such a powerful in-line fan is probably contributing to the issue - a gentler fan might not have been a problem. The reason is that the air is like water or leccy - if you increase the pressure in the hose/wire, leaks are more likely. Ie - some will escape wherever there is a path out.

    Anyhoo, the ultimate solution - I think - would be to contrive a split exit. The only issue then would be the effectiveness of the kitchen extractor as they don't tend to be that powerful in general. What speed do you currently run it at? If 1 or 2, then you'd have to have it on three...

    (Or else wire a supplementary in-line fan to work with it - £20's worth...)
  7. bunhead

    bunhead Member

    That's a real shame, you would be a master tradesman...

    All these things you mention, NO one else knew... The person who installed the system with the hard duct and t jucntion was my plumber , so he should have known about about flow and substances like water etc finding the easiest way out

    Only 20 pounds for another fan... that would be ok!

    The kitchen hood does not do much on 1 or 2. However 3 its really quite powerful. when it goes all the way down the bathroom duct, the force of the kitchen fan is like a mini hair-dryer and makes the shower curtain sway very gently!

    I think because i dont know anyone else , and originally got my plumber to do the ducting as i trusted him, and then another a handyman who i once used before, and it went so wrong, i tried to get quotes from people who were affiliated with checkatrade and trustmark, hoping they would know more.However because they are part of these bodies they charge a lot more and got 2 quotes for £ 1,100 which is scary

    I have attached the picture of the top of the duct by the roof below :0)

    Attached Files:

  8. Thank you. But as many would testify on here, I am a master bull*****r.

    (Except when it comes to Brexit - hey-ho...)

    Ironically, part of the issue you are having may be down to the power of that in-line fan that was fitted - it is almost certain to cause some draught to flow back down any other pipes it has access to. That roof outlet ain't huge, and probably has some flow resistance in it, especially when given a fast flow, so at that point there could be a pressure build-up, so air will try and find other routes to some extent.

    There are backdraught flaps available that fit inside 4" pipes to try and prevent your issue, but I cannot see how they are 100% air-tight, so there's always a risk of some bathroom odours getting back to the kitchen even with one of these fitted.

    Lawdie, I'm not sure what to suggest. Are you not a DIYer to any extent - any chance you can run some ducting yourself? It doesn't have to be pretty, and you have tons of room to play with up there.

    Ok, if this were my hoosie, this is what I'd do. Or, there are two things I would try... The first is more Heath Robinson, but would hopefully do away with the need for backflaps. But, realistically, the 'acceptable' solution would be to use two backflaps and less of the Heath bit.

    First the 'acceptable' solution, which should hopefully work... Very simple and very straight-forward. Fit one of these: ae235.jpg to the grey roof vent adaptor you've shown in your last photo. Attach and seal it well in place.

    Each extractor - kitchen and bathroom's in-line fan - will now have their own completely separate ducting going up to this 'Y' branch. Before attaching the ducting to the Y branch, a backdraught flap should be installed inside each pipe, the correct way around.

    That's it. (Except you'd also have to allow for the condensate collectors...)

    In theory the effect of each air flow would have minimum impact on the other ducting since they only meet at the exit where the back pressure is at a minimum. Therefore the flowing air would much rather go straight oot rather than try and find it's way back down the other duct to the other room. And the backflaps should hinder that even more.

    I can see issues, tho'. How reliable are these backflaps? I can see the kitchen one beginning to stick closed after a year or so once the ducting has a thin layer of grease on it... Since only the force of air will operate them, they will probably (tho' I don't know) be easy to stick closed.

    Because you bathroom in-line fan is sooo powerful, there is also still a risk of some bathroom smells being forced past the backflap and all the way down the kitchen duct to the hood.

    If this were my home I'd go more Heath Rob: I would remove the connector that goes on to the vent grill on the roof. That grey adaptor turns the round fitting in to an elongated rectangular one to suit the vent grill - it looks as tho' it could be secured with a screw at each end? I would then trim a piece of firm PVC sheet to fit inside it, following its internal profile to separate that adaptor in to two halves - this would be fixed in place inside using Stixall. I would then attach te Y branch - and this would also have a PVC 'wall' trimmed and fitted inside to also halve the adaptor. I would then run each extractor's ducting completely separately up to the two ends of the 'Y' and not bother with backflaps. There is a drawback to this idea - apart from no plumber being willing to try it - and that's that the outlet size for each pipe will effectively be halved, so reducing the flow a bit. This would certainly not a problem for the powerful bathroom inline fan, but may affect the kitchen extractor a bit.
  9. bunhead

    bunhead Member

    Well, I am in awe!

    Very creative....

    I just hope i can get someone to do this for me!!

    so with this way does it mean that that they will kind of have 2 separate ducts in a ways they wont ever really join?....:)

    It definately sounds better than using the bacdraft shutter that would stick over time with the grease.

    I will try and get someone to do this.... and see what price they charge. I did see one builder who said he could do it for 500, he is also trustmark rated but he didnt even spot the massive stain by the fan and he never bothers to get back at all ....
    I am trying to get someone who seems to know a little bit what he is doing but they come with an awful price tag

    If I cant get someone who will be willing to try the way you suggest, then i am in the sewage....
    do you know any places i can try where they wont charge to much but have some kind of idea what they are doing?

    If i CANT get someone Then i might then I might have to fibnd someone someone cheap who does not require too much skill to simply reinstall the old original system without any in-line fanm buy and buy a weaker fanwith a long overrun timer

    About DIY... Unfortunately i am not very good at diy...
    I once went on a female empowerment plumbing course to get woemn to be more cofident with DIY. We had to disassemble a toilet and put a new one one in place. Unfortunately we forgot to turn the water off first!! The whole room flooded....
    Deleted member 33931 likes this.

  10. "So with this way does it mean that that they will kind of have 2 separate ducts in a ways they wont ever really join?" Yes, that's the idea with the Heath Robinson method. But I doubt you'll find someone willing to do this - it ain't 'normal'.

    So - I think - the most obvious 'normal' way would be to have both extractors running their outputs in completely separate ducting all the way to the external vent before then having to join them together. But you'd need backflaps. And even then it's no guarantee.
  11. bunhead

    bunhead Member

    where would the best place be to put the back flaps? on each y batch of the y junction?

    I will ask the person who will take a look at it if he can do this your way or with the 2 backlaps... I asked him if over the phone he can cut another exit in the roof and he refused.
    What do you think is better bet? doing the separate ducts that join that may not work, or reverting to the the original set-up and getting rid of the inline fan?

    If trying th 2 ducts joining at the end with potential another fan and reversing the t junction and blocking it off and installing another little kitchen fan, so a combination of sparkilievs and your method.
  12. I just don't know, Buns, sorry.

    I think your issue is compounded by your new fan being so powerful. It drives so much air along that, if it doesn't have a full-flow escape out the external grill, then some air will be trying to work its way back down any other route.

    I also don't know how effective these backflaps are - how air-tight.

    Anyone else on here with thoughts on this?
  13. bunhead

    bunhead Member

    No worries D.A!!

    Thank you for helping me so much before... Really appreciate it :0)
  14. bunhead

    bunhead Member

    I thinking that whatever i do i think a good idea is to get a much less powerful fan.

    The fan will be a silent one so i can run it for 30 mins after use in the bathroom as i gets lots of condensation, and be quiet enough not to bother anyone.
    So although the fan will be mounted in the bathroom instead of the loft:

    1 should still keep the condensation trap ? (never had one before this)
    2 The weakest fan i found online is an intermittent silent fan with a timer, whose strength i can change:
    • Extract performance (FID, M³/h) Max/Min: 54 to / 76
    • Extract performance (FID, l/s) Max/Min: 15 to / 21

    I couldn’t find a weaker constant flow fan that had a good length guarantee (its a 3 years garantee) with a timer on it,and the fan is reduced from £36 to to £23 (Expelair simply silent C4TS square extract fan with timer).
    Unfortunately the weaker fans with a long guarantee and with a timer are only intermittent fans

    They have some intermittent or axial fans that are a bit stronger but i will not be able to adjust the strength if i find that the fan is still too strong for my duct. Their airflow is at around 21 (FID, l/s)

    3. Is an inconstant fan appropriate?

    i was wondering if an inconstant flow fan is appropriate for either scenario,( splitting the duct to join near the top of the roof, or keeping it to the very original isntallation).

    My old fan that was vented to share the kitchen duct was was a 20 year old greenvac fan that ran constantly, not intermittent
  15. It's a bit of a 'mare, Buns. It's all a bit of a compromise due to the fact you only have a single external outlet.

    If you end up having to fit backflaps, then these will add to the flow friction so reducing the volume, so making your bathroom extractor less effective. Your current fan would cope no problem 'cos it's well powerful, but if you fit an asthmatic fan which already has to puch the air through a few metres of ducting, and then add a backflap to that, then gawd knows.

    And gawd ain't telling me.

    Sorry - I don't really know what to advise. And it doesn;t look as tho' others on here have such ducting experience either.

    I'd search for more plumbing forums, specifically ones that deal with this sort of issue. You essentially want to know the best answer to "Can I have two extractors working through a single external vent?"

    A solution that would work is to have your inline fan wired to both extractors so it comes on with either the kitchen or bathroom switch. But that's not ideal either.
  16. bunhead

    bunhead Member

    Thank you D. A

    although the situation is grim , your posts are funny and often make me smile

    Yes, It does seem to be a 'mare, From Buns! :)
  17. DIYDave.

    DIYDave. Well-Known Member

    Although I was the 1st to comment on ur post, haven’t really been following it and now it’s got soooooo long, it’s nearly sent me to sleep b4 my dinner ;)

    I may have this wrong and sorry if it’s been mentioned somewhere in the acres of above text but, looking at 1st pics, it’s a weird set up indeed

    So the kitchen extract (RH side in ali duct) comes from extractor fan above hob, then is kinda boosted by the in-line fan, which was actually fitted for the bathroom, thus giving problems in the bathroom with odours and blowing shower curtains

    Simply extend ali duct and bypass in-line fan, T into vertical soil pipe say half way up

    Luckily all the soil pipe fittings are just push fit so can be removed and reused. Shouldn’t be much wasted materials to re-route and/or expense to extend ali duct

    Has this been mentioned so far ??
    Not really got the inclination to read through entire tome ! :D
    Deleted member 33931 likes this.
  18. bunhead

    bunhead Member

    Hi Dave,

    I don’t think that has been mentioned yet! Thank you...:)
    PS Better you sleep before diner rather than after:D
  19. That hans't been mentioned, Dave, and if it works it would be very simple and cheap to do.

    It does carry the same old risk, tho' - once the powerful in-line fan is on, it delivers so much air flow that pressure will slightly build up in that vertical pipe since the ext grill ain't that big. If so, this will then force some of that bathroom 'air' back down your new Tee and extended duct, right back to the kitchen.

    But, surely worth it as an initial step? If so, simply cut that vertical pipe high up (as near the ext vent as posisble) as Dave says, fit one of these: s-l640.jpg (upside down, of course) and connect the branch to your extended ducting to the kitchen extractor.

    Try it and see.

    If smells do go the wrong way - kitchen to bathroom or vicky-verka - then fit flaps in each inlet to that Y branch.

    Attached Files:

  20. DIYDave.

    DIYDave. Well-Known Member

    Sometimes a fresh pair of eyes looks at the sitaution a little clearer :)

    I think the cause of the issues are now obvious (I was tempted to have a scan through the previous mutterings after all) - c rap on tv but the wife’s silent !

    1. With the kitchen extract ON but the bathroom fan OFF, the air, laden with cooking odours and moisture is slamming into the stationary blades of the in-line fan

    Some of that air will find its way through, although at a much reduced rate and quantity. The majority (I would guess) will take the easiest option and travel back down into bathroom - hence smells and fluttering shower curtain

    2. The reduced air flow, speed and subsequent turbulence will cause the extracted air from kitchen to cool down quicker and shed more of its moisture, just as it enters the in-line fan enclosure and hits the stationary blades. Take another look at the 1st couple of pics you posted. You can clearly see water stains on the loft floor at this point - entrance to fan. This water is clearly coming from the kitchen extract when your boiling ur peas and bathroom fan is OFF. It’s not getting as far as to make use of the condensation trap

    Time to re-jig pipes........ yet again :mad:

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