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Fundamentals: Trickle Ventilator problems

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    • CommentAuthortony
    • CommentTimeMar 7th 2026
     
    Trickle ventilators

    During the 2021/2022 season at DraughtBusters we started to encounter a lot of problems with trickle ventilators. These have been even more of a problem prevalent in 2026.

    Some of the problems are : -

    Draughty when closed
    Insect protection gone or decayed
    Wouldn’t or couldn’t close
    Householder didn’t know how to open or close them

    Draughty when closed.
    We found that in a lot of cases draughts were emanating from the trickle vents even when closed. These vents were surprisingly insubstantial and it was rather a shame to find that they were letting in draughts. It would be possible to seal them to the frames to prevent some of the draughts but this would be tricky. If the windows can be used on a ventilate position, i.e. fixed in a secure vent position using the second position on the window handle then we recommend sealing up the trickle ventilators.

    Insect protection gone or decayed.
    We have identified whole estates where trickle ventilators have lost their insect protection, these are often with ‘over the head’ type ventilator arrangements. The insect grilles become brittle and fall out or are knocked out with window cleaner’s brushes.

    Won’t close - this is different from draughty when closed as those do close but a draught enters between the frame and the vent. Some ventilators have plastic clips that hold the vent in place and these can break and the vent flaps about remaining open all the time, others just don’t close and allow draughts all the time even when closed.

    Householder can’t open them, we didn’t like this one! There are a lot of different types of trickle ventilators many and varied ways of opening them some push left or right some up and or down, others click open, while others need a sharp but gentle press. It is nor really surprising that some people can’t open them.

    Trickle ventilators are the bane of a DraughtBusters life, they are intended to let draughts in, in a controlled way. They are proving themselves to be unfit for purpose. We see ventilation as an active thing, to be controlled by occupants as and when required and a general government directive of ‘one size fits all’ is resulting in draughty homes. We have said before that draughts do too much by way of ventilation when it is windy and not enough when it is calm. Trickle ventilators should now be outlawed in favour of saving energy. Controlled ventilation is what we need.

    The adage, ‘build tight ventilate right’ is a very good one, unfortunately trickle vents although the intention was for them to help have turned out to be unhelpful, they cause draughts as highlighted above, do not ventilate right and it will take a lot of work to rectify the situation. Sadly this is a repeat of the same mistake made in the fifties with compulsory through the wall vents in all bedrooms in new homes, DraughtBusters expend a lot of effort blocking those ones up even two generations after they were installed.

    The next generation of DraughtBusters will need to spend even more time sorting out leaking trickle ventilators in windows.
    •  
      CommentAuthordjh
    • CommentTimeMar 7th 2026
     
    So options:
    (1) make everybody install MVHR - problem solved
    (2) are there any good trickle ventilators that the draughtbusters have identified? If so, replace every trickle ventilator in the land with a known good one!
    (3) Teach everybody how to perform Stoßlüften
    •  
      CommentAuthorfostertom
    • CommentTimeMar 7th 2026 edited
     
    (2) trickle-type vents that have built-in humidity sensors tend to be much higher quality (and cost), as well as regulating ventilation-or-not intelligently (humidity is a fair proxy for CO2 concentration).
    • CommentAuthortony
    • CommentTimeMar 7th 2026
     
    Thanks for the comments, I agree that an incredible number of them need to be replaced or sealed up.
    The best ones we have seen apart from not having then are Velfac ones.
  5.  
    Have you had any dealings with the Glidevale Acoustic Energy Saver, (Humidity-sensitive) vents?

    https://www.bpdstore.co.uk/glidevale-acoustic-energy-saver-humidity-sensitive-trickle-ventilator/p/183

    I'm just about to pull the trigger on these as part of their i-PSV system, although I will need to make some adaptors as the current ventilators are wider. Eye watering prices...
    •  
      CommentAuthorfostertom
    • CommentTimeMar 9th 2026 edited
     
    Interested to hear what was your thinking to specify such a system. Does one of these provide enough flow for a typical(?) room? If so, gd value, neatly providing as it does the per-room 'intelligence' in the system.
    • CommentAuthortony
    • CommentTimeMar 9th 2026
     
    The Scottish results on trickle ventilators showed that they work best with the door open ?
    • CommentAuthorsgt_woulds
    • CommentTimeMar 10th 2026
     
    The iPSV system does need door undercuts or vents between rooms to allow air to flow to the central extract point. Internal vents are also moisture controlled.

    (Bathrooms and utility rooms are on a seperate stack and need to draw air into the rooms from heated parts of the building, so again, door undercuts required. No trickle vents on the bathroom windowas this would feel cold on wet skin).

    There is a pretty good corellation between moisture levels and CO2, so if we can draw in fresh air and control via moisture we should be golden.

    low Installation and maintenance costs and zero running expense is a major attraction of iPSV, as is the absolute silence of operation.

    I'm planning to trail it in the bathroom and utility room first. If it works effectively and doesn't feel 'draughty' then we'll roll it out in the other rooms.
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2026
     
    Posted By: sgt_wouldsThe iPSV system does need door undercuts or vents between rooms to allow air to flow to the central extract point.
    Just to note that an alternative to undercutting doors is to cut a channel in the back of the architrave head at the top of the door. I don't remember where I read about the idea (was it here?) but I can confirm that it works well and gives better sound isolation and appearance (it's invisible).
    • CommentAuthorsgt_woulds
    • CommentTimeMar 11th 2026
     
    I like that Idea, will have to look into it :-)
    •  
      CommentAuthorfostertom
    • CommentTimeMar 11th 2026
     
    Passive ... what size central 'extract' duct does it need, and how tall, to create 'chimney effect'? BedZED-era schemes had enormous ducts complete with cowls that turned away from the wind to create an extraction vacuum.
    https://static.wixstatic.com/media/330c42_5d1c0d537326429b88090179e4855ad0.jpg/v1/fit/w_2500,h_1330,al_c/330c42_5d1c0d537326429b88090179e4855ad0.jpg
    • CommentAuthorGreenPaddy
    • CommentTimeMar 11th 2026
     
    @djh - also liking this idea being less visible, but I'm not quite visualising the air passage route. Want to steal this idea, so would like to understand it. Is it between the door frame and the structural opening?
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2026
     
    Yes, the back of the head of the architrave is cut away (our doors are 832 mm wide, so we rebated 10 x >762 out of the back). I don't remember exactly how the air gets from one side to the other. Maybe we rebated the head of the door frame? I suppose it might have been the structural timber above that, or even an existing gap?
    • CommentAuthorsgt_woulds
    • CommentTimeMar 11th 2026 edited
     
    I installed the GGL solar on Bed zed, and the solar panels on the later Rural zed.

    These were interesting projects that included lots of inovative solutions, not all of which worked, but the passive stack ventilation was successful.

    You don't need a very high stack to get a good passiv draw. Working on most roofs in winter, if you remove a tile and there was a gap in the felt, you could feel the warm air gushing out.

    The Bed zed directional cowls were intended to create more draw in summer conditions when cooler internal air is less boyant. This was important as their projects, espescially Rural zed used a lot of decrement delay, which kept internal temperatures noticably cooler in summer.

    The buzz word at the time was 'Thermal Mass'. I remember having a long discussion with one of their architects at Rural zed whilst watching them fill all the floor voids with seived soil to increase the mass of the building.


    Incidentally I got rudely booted out of a meeting on site at Rural zed. We based our PV design and dimensions off their planning drawings. Later, when I turned up at the site to check the shading and as-built dimensions I had a bit of an issue:

    After measuring the footings 3 times I popped into the site managers office to report that they were building it nearly 1.5 meters too short. I was informed that I was 'an Incompetent F*%$£It, and should learn how to use a tape measure. They'd used laser measures for the setting out and knew exactly what they were doing and I should just Foxtrot Oscar back to my nice warm office.

    I just redesigned our PV system based on the reduced dimensions and submitted it to the customer, along with our revised - and obviously reduced - kWh production estimates.

    Which came as a great surprise to them, and prompted them to make their own measurements... Whoops :-)
    • CommentAuthorsgt_woulds
    • CommentTimeMar 11th 2026
     
    I'm also thinking that it would be easier to fit intumescant fire proofing strips in a slot behind the architrave than find one suitiable for a larger door undercut.

    I assume the more convoluted air path is what attenuates the sound?

    I do wonder if less air would be drawn through the top of the door compared to the bottom due to warm air stratification
    •  
      CommentAuthorfostertom
    • CommentTimeMar 11th 2026 edited
     
    Great Zed stories! He was There.
    Any idea if those cowls still rotate at a touch?
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2026
     
    Posted By: sgt_wouldsI'm also thinking that it would be easier to fit intumescant fire proofing strips in a slot behind the architrave than find one suitiable for a larger door undercut.
    Well the size of the door undercut is the same as the architrave rebate and is set by building regs.

    I assume the more convoluted air path is what attenuates the sound?
    I assume so too.

    I do wonder if less air would be drawn through the top of the door compared to the bottom due to warm air stratification
    Dunno, Ours is propelled by the MVHR, which is a constant volume model.

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