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The Passyfier Sleeved 75AB is a compact through-wall dehumidifier vent for targeted condensation control in small spaces such as cupboards, box rooms and utility stores up to 5m². It is a non mechanical, silent solution that allows trapped water vapour to diffuse to the outside without creating uncomfortable draughts or noticeable heat loss.
The kit includes a white internal grille with a built in fly screen, a preformed external louvred airbrick sized 210mm x 65mm and a telescopic sleeve that suits 100mm - 345mm wall thicknesses.
With a maximum water vapour transmission of 0.75L per 24h and simple, tidy installation that can replace a single airbrick opening, it delivers reliable background moisture control with zero running cost.
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✔️ Passive through wall dehumidifier vent for small spaces up to 5m², silent with zero running cost.
✔️ Diffusion based moisture removal reduces condensation and black mould without draughts or noticeable heat loss.
✔️ Fits a single airbrick opening using telescopic sleeve adjustable 100mm to 345mm, ensuring tidy retrofit installations.
✔️ Includes white internal grille with flyscreen and louvred external airbrick for clean aesthetics and tempered draughts.
✔️ Transmits up to 0.75 litres water vapour each day, supporting healthier humidity in cupboards and box rooms.
Passyfier Sleeved 75AB Dehumidifier Vent is a passive solution for compact, enclosed rooms where moisture build up leads to black mould, stale odours, and damage to finishes. By creating a controlled diffusion path through the wall, it allows excess water vapour to escape continuously without fans, motors, or noise. The result is steady background drying that lowers the risk of condensation on cold surfaces and improves everyday comfort.
The operating principle is straightforward. During the heating season indoor air typically carries a higher vapour pressure than outdoor air, so moisture naturally migrates outward. The vent’s sleeved passage and louvred terminations enable this vapour movement while resisting direct through air currents, keeping perceived draughts to a minimum and preserving indoor comfort. This passive process runs quietly around the clock and does not add to energy bills.
The kit is engineered for quick retrofit and clean new build work. The outer duct measures 204 mm by 60 mm to suit a nominal single airbrick opening, and the telescopic sleeve adjusts on site to match common wall depths from 100 mm to 345 mm. A supplied plastic wedge sets a slight outward fall so any incidental moisture drains safely. Internally, a discreet white grille with an integrated flyscreen provides a tidy finish and can be removed for occasional dusting, while the slim external louvred airbrick tempers wind effects and keeps the façade neat.
Because the system is non mechanical there are no electrics to maintain and no running cost. The vent works continuously, transmitting up to 0.75 L of water vapour per 24 hours under typical domestic conditions. It is ideal for smaller rooms where persistent background humidity is the issue rather than short bursts of steam. Used alongside compliant mechanical extract in kitchens and bathrooms, it forms part of a complete, quiet, and economical moisture control strategy.
In practice the vent helps create a drier, fresher environment that resists condensation and limits the conditions in which mould can take hold. Decorations last longer, stored items are better protected, and the overall feel of the space improves without increasing energy use. By removing vapour at source while avoiding large volumes of cold outdoor air, the Passyfier approach is kinder to the building fabric and supports long term indoor air quality.
Targeted Condensation Control For Small Spaces: Designed specifically for cupboards, box rooms and compact stores up to 5m² where background humidity lingers and causes mould.
Passive And Silent Operation: Non mechanical design works continuously without electrics, noise or user input, so there is nothing to switch on and no running cost.
Minimal Heat Loss With Low Draught Risk: The sleeved passage and louvred terminations allow vapour to diffuse out while resisting bulk airflow, which keeps the room comfortable.
Quick, Tidy Retrofit: Outer duct sized to replace a single airbrick opening and a telescopic sleeve that adjusts on site for 100–345mm wall thicknesses makes installation straightforward.
Clean Interior Finish: Supplied white internal grille with built in fly screen keeps insects and debris out and lifts out easily for light cleaning.
Reliable Moisture Transmission: Up to 0.75L per 24h under typical domestic conditions stabilises relative humidity and helps prevent black mould on cold corners and stored items.
No Power And No Maintenance Burden: With no motors or filters to service, upkeep is limited to an occasional wipe of the internal grille.
Cupboards And Built-In Wardrobes: Background drying of enclosed storage where clothes and fabrics are prone to musty odours.
Box Rooms And Small Bedrooms: Continuous moisture control in compact habitable rooms up to 5m² that suffer from window streaming and cold corners.
Utility Stores And Under-Stair Spaces: Helps prevent condensation on cold masonry and on stored belongings in partially heated areas.
Refurbishment Of Older Properties: A neat replacement where an open airbrick caused discomfort yet humidity remained high.
Outbuildings And Ancillary Rooms: Suitable for solid, cavity and timber frame walls where quiet, zero-energy background ventilation is desirable.
Maximum Served Floor Area: 5m² per vent.
Water Vapour Transmission: Up to 0.75L per 24h.
External Louvred Airbrick Face: 210mm × 65mm.
Outer Duct Size: 204mm × 60mm.
Wall Thickness Range: 100-345mm with telescopic sleeve.
Internal Grille: White with integrated fly screen, removable for cleaning.
Supplied Accessories: Plastic wedge to create outward fall, installation instructions.
Construction Suitability: Solid walls, cavity walls and timber frame walls.
Operating Principle: Passive vapour diffusion with draught-limiting terminations.
Energy Use And Noise: Zero energy consumption and silent in operation.
Work from a safe, stable platform with adequate edge protection and lighting. Wear suitable clothing together with safety goggles, cut-resistant gloves and a dust mask when drilling or cutting masonry. Check the work area for live services before you begin and never cut through load-bearing lintels or damp proof courses.
Keep the area below clear of people and belongings because debris may fall during core cutting or stitch drilling. Handle cement, sealants and fungicidal washes in line with the manufacturer’s guidance and wash hands after use. If you are unsure about any through-wall work, engage a competent builder.
Install the vent in the problem location rather than simply selecting a convenient wall. Choose the cupboard, box room or small space that shows visible condensation or mould, then pick an external wall position that is high on the wall and no more than 300mm below the ceiling. A high-level position matters because the warmest, moisture-laden air collects near the ceiling, so placing the vent here improves vapour diffusion while keeping any perceived air movement away from occupant level.
Aim for the colder, stale corner furthest from the doorway where practical and keep the internal grille clear of shelves, coats or stored items that might block it. Confirm that the wall thickness is within the kit’s range. The 75AB sleeve suits walls from roughly 100mm up to about 345mm; if the wall is thinner than the supplied sleeve length, plan to trim the inner duct on site.
Assemble tools such as a masonry drill or small core bit, a means to form a neat 9 x 3 inch opening, screws and plugs, a pointing trowel, a cartridge of suitable interior mastic and the supplied plastic wedge that creates the outward fall through the wall.
The 75AB is designed for small areas up to 5m² and provides passive background moisture control. It does not replace rapid mechanical extraction in kitchens and bathrooms and it must not be used to supply combustion air to gas, oil or solid-fuel appliances.
Always set a slight outward fall on the sleeve so any incidental moisture drains to outside. Seal any open cavity interface internally to prevent bypass draughts. Treat existing mould with a quality fungicidal wash before redecorating so you begin with clean surfaces. In very cluttered cupboards, create a little space around the internal grille to let vapour reach it freely.
Mark the position on the internal face at high level in the affected small room, keeping the top of the vent within 300mm of the ceiling and clear of pipes, cables and lintels. If you prefer, drill a small pilot hole at the intended centre line to transfer the position to the outside.
Form the external opening by marking a neat 9×3 inch rectangle in the outer leaf. On rendered walls the foamed polystyrene transit packaging makes a handy template for marking out. Carefully cut or stitch-drill the opening and square the edges.
Return indoors and cut the matching 9×3 inch aperture through the inner leaf using the pilot hole as a datum so the two openings align. Clean out debris and lightly mist the reveals if you will be bedding into mortar.
Dry-fit the sleeved duct from inside to check length and alignment. If the wall is thinner than the supplied sleeve, trim the inner duct to suit so the external louvred airbrick and internal plate will sit flush when fixed. Offer the supplied plastic wedge at the internal end to create a small outward fall through the wall; a drop of around 5–10mm across the duct is ideal.
Support and bed the duct in place. Where you are bedding with mortar, press the assembly home so the external airbrick sits neat and level on the façade and the internal plate lands square to the inner wall. Ensure the duct maintains its outward fall and is not twisted.
Provide an internal seal if the duct crosses an open cavity. Run a continuous bead of mastic around the penetration on the room side to prevent unintended airflow bypassing the diffusion path.
Fix the external louvred airbrick face securely once bedding has taken an initial set. Use the screws and wall plugs provided and avoid overtightening. If you need to delay this step to allow making-good or plastering, keep the opening protected until you complete the fix.
Fit the internal white grille with the built-in fly screen. The grille housing secures with the short fixing screws provided. To remove it in future for cleaning, gently deflect the top edge toward the centre with a thin flat blade at the indicated point.
Make good around the opening and clean down. Vacuum dust, wipe nearby surfaces and wash any previously affected areas with a fungicidal wash following the manufacturer’s instructions before redecorating.
Explain that the vent is passive and always on. There are no controls, electrics or running costs. It works by allowing moisture vapour to diffuse out while its internal design limits draughts.
The grille must remain unobstructed by coats, boxes or shelves to be effective. In use, occupants should keep doors closed during steamy activities in adjoining rooms and then open them afterwards for cross-ventilation.
There are no moving parts and routine care is minimal. Wipe or lightly vacuum the internal grille and fly screen once or twice a year to remove dust and cobwebs
Check the external airbrick face occasionally to make sure it remains clear of debris. If you ever remove the internal grille for cleaning, take care not to disturb the slight outward fall or the internal mastic seal around the penetration.
If the area previously suffered from mould, wash walls, ceilings and shelves with a good fungicidal wash and allow them to dry completely before repainting. A mould-resistant paint is sensible in stubborn spots.
Maintain steady background warmth in colder months so indoor air can carry normal moisture loads without condensing on cold surfaces. If the small room is part of a larger space that remains damp, consider a second vent in a nearby position or review extract fan performance in wet rooms.
The Passyfier Sleeved 75AB is intended for compact spaces such as cupboards and box rooms. A single unit serves up to 5m² and can transmit up to 0.75 litres of water vapour per 24 hours under typical domestic conditions.
It fits a neat 9 x 3 inch wall opening and accommodates wall thicknesses from roughly 100mm to about 345mm with on-site trimming where necessary. The kit includes a white internal grille with integrated fly screen, a sleeved duct with diffusion media, a plastic wedge to set the outward fall and fixings with instructions.
The external louvred face is sized around 210 x 65mm to suit a standard single airbrick opening. When installed high on the wall with a gentle outward fall and a sealed cavity interface, the 75AB provides quiet, low-loss background moisture control around the clock and costs nothing to run.
A) The Passyfier Sleeved 75AB Dehumidifier Vent is a compact, through-the-wall passive vent designed to tackle background condensation in very small spaces such as cupboards, box rooms and utility stores up to 5m². Instead of using a fan, it relies on natural vapour diffusion to let trapped water vapour migrate outdoors while its sleeved passage and louvred terminations resist direct through-draughts. This helps stabilise indoor relative humidity, reduces window streaming and cold-corner damp, and limits the conditions that allow black mould and musty odours to form. Because it is non-mechanical it operates silently around the clock with zero running cost and virtually no maintenance. The kit is sized to replace a single 9×3 inch airbrick opening neatly, making it ideal for retrofit where an open vent felt too draughty but humidity still lingered after insulation upgrades.
A) The Passyfier Sleeved 75AB uses the natural difference in vapour pressure between warm indoor air and cooler outdoor air, especially during the heating season. Moisture molecules move from higher to lower vapour pressure and are encouraged to diffuse outward through the vent’s warm, telescopic sleeve. The internal grille and external louvred airbrick are shaped to limit bulk airflow, so you do not experience a free jet of cold air as you would with an open hole. The mechanism is diffusion rather than forced ventilation: it works continuously, silently and with minimal heat loss, trimming background humidity between high-intensity events such as showering or cooking. In typical domestic conditions a single unit can transmit up to 0.75L of water vapour per 24 hours, which is proportionate for small, enclosed spaces where persistent damp has appeared.
A) Fit the Passyfier Sleeved 75AB high on an external wall of the affected small space, keeping the top of the internal grille within about 300mm of the ceiling. Warm, moisture-laden air pools near the ceiling, so a high-level position maximises vapour diffusion while keeping any slight air movement above occupant level. Select the colder, stale corner that is furthest from the doorway and keep the grille clear of coats, shelves and stored items. The outer duct is sized 204×60mm to suit a 9×3 inch opening, with an external airbrick face of roughly 210×65mm, so it commonly replaces a single airbrick neatly. Always set a slight outward fall using the supplied wedge so incidental moisture drains outside, and seal where the sleeve crosses an open cavity to prevent bypass draughts that could dilute performance.
A) One Passyfier Sleeved 75AB is intended for compact spaces up to 5m². In typical domestic conditions it can transmit up to 0.75 litres of water vapour per 24 hours, which is appropriate for cupboards, small bedrooms, under-stair stores and utility spaces where background humidity lingers. If the area is unusually cluttered, very cold, or larger than 5m², consider improving airflow paths to the grille, reviewing extraction in adjacent wet rooms, or using additional vents in nearby positions. Remember that the 75AB manages the ongoing background load; compliant extractor fans in kitchens and bathrooms are still needed to clear short-term spikes quickly. Treat any existing mould with a fungicidal wash before redecorating so you start from clean, dry surfaces and can judge the improvement accurately.
A) The Passyfier Sleeved 75AB is specifically designed to minimise felt draughts and thermal penalty. The sleeved passage provides a warm diffusion path, while the internal grille and external louvred airbrick temper pressure effects so the space does not feel cold or blowy like it can with an open airbrick. Installed near the ceiling, any moderated air movement is kept above occupant level and is rarely noticed in everyday use. Good detailing matters: create a slight outward fall through the wall, seal around the penetration, and avoid covering the grille. In practice the space feels drier and more comfortable at the same thermostat setting because surfaces are less prone to condensation, which is often perceived as “chill” even when the thermostat has not changed.
A) No. The Passyfier Sleeved 75AB provides passive background moisture control for small rooms and cupboards, and works alongside compliant mechanical extract in kitchens and bathrooms. Extract fans remove short-term humidity spikes from showering and cooking; the 75AB trims the ongoing moisture level between those events in adjacent tiny rooms where damp persists. This complementary approach mirrors good practice and delivers the best outcomes. Keep doors closed during moisture-producing activities, then open them afterwards for cross-ventilation. Maintain steady background heat in colder months so indoor air can carry normal moisture without reaching dew point on cold surfaces. Used this way, the 75AB helps prevent musty odours and mould on stored items without adding to energy bills or noise.
A) The Passyfier Sleeved 75AB kit includes a telescopic sleeve to suit wall thicknesses from about 100–345mm, a white internal grille with an integrated fly screen, a preformed external louvred airbrick (face approximately 210×65mm), a plastic wedge to set the correct outward fall and installation instructions. For installation you will usually need a means to form a neat 9×3 inch opening (stitch drilling and careful cutting, or replacing an existing airbrick), basic masonry bits, suitable wall plugs and screws, a pointing trowel, a quality mastic for internal sealing around an open cavity, and general hand tools for fixing and making good. If the sleeve is too long for a thin wall, trim the inner duct carefully so both internal and external faces sit flush and square when fixed.
A) The Passyfier Sleeved 75AB is a passive, non-mechanical dehumidifier vent for small spaces up to 5m². Under typical domestic conditions it can transmit up to 0.75L of water vapour per 24 hours. The sleeved outer duct measures about 204×60mm to suit a single 9×3 inch opening, while the external louvred face is approximately 210×65mm. The telescopic sleeve adjusts on site for wall thicknesses from roughly 100–345mm and is supplied with a wedge to create a slight outward fall. The internal grille is white with an integrated fly screen and can be removed easily for cleaning. The unit suits solid walls, cavity walls and timber-frame construction. Operating principle is passive vapour diffusion with draught-limiting terminations; energy use is zero and operation is silent.
A) Identify the most affected small space and mark a high-level position on an external wall, keeping the top of the grille within about 300mm of the ceiling and clear of services. Form a neat 9×3 inch opening through the outer leaf, then the inner leaf, keeping the edges true so the faces sit flush. Dry-fit the telescopic sleeve from indoors, trimming the inner duct if the wall is thin. Insert the supplied wedge at the internal end so the sleeve has a small outward fall, typically 5–10mm across its length. Bed the assembly carefully so the external louvred face is level and square, then seal around the penetration on the room side if the sleeve crosses an open cavity. Fix the internal grille, make good the edges and clean down. The vent will then operate continuously with no user input.
A) The Passyfier Sleeved 75AB suits solid masonry, cavity walls and timber-frame construction, making it practical for both retrofit and new build. In cavity walls, maintain a continuous sleeve across the cavity and apply an internal mastic seal around the penetration to prevent bypass draughts. In timber-frame, respect sheathing and weather-barrier details and seal neatly to preserve envelope integrity. Always site the vent high on the wall, keep the grille unobstructed by shelves or clothing, and avoid proximity to heat sources that could soften plastic components. Choose an external position with a clear route to atmosphere and a degree of shelter where possible. Good siting and sealing preserve comfort and ensure reliable moisture diffusion year-round.
A) The Passyfier Sleeved 75AB has no motors, sensors or replaceable filters, so upkeep is minimal. Once or twice a year, lightly vacuum or wipe the internal grille and fly screen to remove dust and cobwebs. After storms or heavy leaf fall, glance at the external louvred face to ensure it remains clear. If redecorating, avoid painting over the grille slots or the external louvres as this can restrict diffusion. Check that the slight outward fall has not been compromised by later making-good. Provided the grille stays unobstructed and seals remain intact, the vent will continue to operate silently and effectively for many years with no further intervention or running costs.
A) The Passyfier Sleeved 75AB treats background airborne moisture in small spaces up to 5m²; it does not replace compliant extractor fans in kitchens and bathrooms, and it must not be used to supply combustion air to gas, oil or solid-fuel appliances. It is not a cure for liquid water issues such as leaks, rising damp or penetrating damp, which must be remedied at source. Performance is reduced if the grille is blocked by coats or shelving, if the sleeve lacks an outward fall, or if a low-level location is chosen where high-level siting would have been feasible. Treat any existing mould with a fungicidal wash before redecorating so staining does not mask results. Observing these limits maintains comfort and ensures dependable dehumidification.
A) Mount the vent high so the top of the grille sits within about 300mm of the ceiling and keep it clear of stored items. Use the supplied wedge to set a small outward fall and form a continuous internal mastic seal where the sleeve crosses an open cavity. Maintain steady background heat in colder months so indoor air can carry normal moisture without reaching dew point on cold surfaces. In cupboards, create a little breathing space around the grille and avoid over-packing shelves. Continue using extractor fans diligently in bathrooms and kitchens, keeping doors closed during steamy activities. If a neighbouring area also suffers damp, consider a second 75AB in an adjacent position. Starting with clean, dry surfaces after a fungicidal wash makes improvements easier to see.
A) Most users notice reduced musty odours and less surface moisture within the first week of normal use, especially during colder spells when condensation risk peaks. Black mould must be treated and redecorated, so visible improvement depends on aftercare as well as humidity reduction. Allow a full heating cycle or two to assess the change while maintaining good habits with extractor fans and background heating. If results are slower than expected, check that the grille is unobstructed, the external airbrick is clear, the sleeve has a slight outward fall and cavity bypass paths have been sealed. In very cluttered cupboards, creating breathing space around the grille often accelerates stabilisation and helps the passive diffusion pathway do its job.
A) Yes. The Passyfier Sleeved 75AB is engineered around a single airbrick module. The outer duct measures approximately 204×60mm and the external louvred face is roughly 210×65mm, so it typically replaces a 9×3 inch opening with a tidy finish. The telescopic sleeve adjusts to common wall thicknesses from about 100–345mm, allowing precise, square seating of the faces inside and out. Indoors, a minimalist white grille with a built-in fly screen presents a clean appearance that suits cupboards and small rooms, and lifts out easily for occasional dusting. Because the vent is compact and installed near the ceiling, it remains unobtrusive in day-to-day use while operating silently in the background with zero energy use.
A) Leaving a window ajar or relying on an open airbrick admits bulk airflow that can feel draughty and waste heat, encouraging occupants to close the opening and allowing humidity to build again. The Passyfier Sleeved 75AB provides a warm, sleeved diffusion path that resists free through-draughts while letting moisture vapour escape continuously. Installed high on the wall, it keeps any moderated air movement away from occupant level and operates silently 24/7 with no user input. In practical terms this improves comfort and compliance, keeps background humidity more stable, and reduces mould risk without compromising security or energy use. Combined with proper fan extraction in wet rooms, it offers a balanced, low-energy strategy for long-term moisture control in small spaces.
A) The Passyfier Sleeved 75AB suits both retrofit and new-build. In retrofit it commonly replaces a single 9×3 inch airbrick, swapping an uncontrolled opening for a draught-limiting diffusion pathway. The installer forms or cleans up a 9×3 inch aperture through both leaves, dry-fits and adjusts the telescopic sleeve to the wall thickness (100–345mm), sets a slight outward fall using the supplied wedge, seals where the sleeve crosses an open cavity, beds the external louvred face level to the façade and fixes the internal grille. Making-good is minimal because the module is compact and rectangular. In new-build the same detail is set high on the wall of small rooms and cupboards to provide silent, zero-energy background dehumidification that complements kitchen and bathroom extract fans for a complete moisture management approach.
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