Humid and mouldy! Installing MVHR ventilation (Kair system) 

How did I fix the soundproofing problem? More here: members.gosforthhandyman.com/soundproof-mvhr-vent/ Don't forget to follow me on X for loads of secret things: twitter.com/gosforthandy 👍😁

"The humidity is never going to get below whatever the humidity is outside" - not so if you have any form of heating in the room such that the room is warmer than outside. Humidity readings in % are *relative* humidity - it's a measure of how much moisture is entrained in the air relative to the maximum amount the air can hold. That maximum amount is in turn dependent on temperature. Cold winter air can have 95%+ RH but contain very little moisture. Bring that air into a room, heat it up to room temp and the RH will drop to 30-40%. I've never understood why we don't quote humidity using an absolute scale, like ml per cubic metre or something. We'd all get used to what readings constitute dry, normal, jungle etc and it would save all this confusion that RH generates by introducing the temperature variable.

Don't forget the registered "humidity" is relative humidity which depends on temperature. If the outside temperature is lower then 70% humid air has less water vapour than 70% humid air inside. As the air from outside is pulled inside it's relative humidity will drop as it warms up.

As a suggestion (it’s not everyone’s cup of tea) do a raspberry pi project. Possibly run home assistant on it. Then you can use any number of products to record humidity and co2 and then switch things on or off based on that data.

Andy, just a quickie as the topic of the video was safety! The electrician in me spotted you had some sort of transformer plugged in, in the corner, via one of those lethal unfused Chinese mini 3 pin plugs. If you're leaving that on, or really even if you're not, please consider binning it and replacing it with something less likely to go woof! Usually the wire inside the lead is only single sheathed too, so much more vulnerable to damage. All the best and keep up the great videos.

That Cedar is gorgeous.

On humidity, remember that it's relative to temperature. Warm air holds more water. 70% humidity at 15°C is only 50% at 20°C. Something to keep an eye on if you find it feeling too dry in winter.

I'm rennovating at the minute: and to store all my tools and materials, plus all the extra stuff you end up dragging with you when you move I put up a large garage tent. I put down a levelled MOT bed and loads of pallets topped with 18mm OSB as a base so there's air able to get underneath it thinking that would help. Not al ALL. It would RAIN in there! All my tools got rusty and there was mould everywhere! This year during the dry summer months I have installed a bathroom ventillator, and fingers crossed if I leave that running in the winter evenings/mornings it will keep it dryer in there this year!

You have a HRV Heat Recovery Ventilator which is only concerned with Heat, ERV Energy Recovery Ventilator balances heat and moisture in the air (keeping heat and humidity on the side where it came from with like 85% efficiency or so) This uses a special membrane instead of just a heat sink like a HRV, so it is more expensive and requires more complexity of ducting (from what I've seen) My understanding is that warm places all year round are fine with HRV since they have ACs to act as dehumidifiers, but northern colder climates where the temp is way lower, need ERV to keep moisture in during the winter (and to help keep it out in the summer)

we had a garden building built as a gym about 15 years ago now, and at first it was also a sort of tool storage on one end where i'd moved an old wardrobe that covered most of one wall. Eventually got around to putting up a shed and moving the tools in there. So claimed back that space for gym equipment. I noticed the weight rack on that wall the weights were getting a bit of rust on any worn patches in the paint, and when was taking down the old wardrobes i did notice there was a bit of mould on the back of them. but they had been there for probably a decade so i didnt think too much of it. The cause turned out to be a result of when it was built that wall on the outside the ground level was pretty much right up to the damp course, and the builders didnt do anything to sort that, and just filled back in with dirt and a pointless bit of decorate gravel on top and so with rain splashing and the lack of sun in that narrow gap between the wall and fence that wall was always wet. So i had to dig out to below the damp course and put in a french drain with a pipe connected to the downpipe drain, and it solved the problem of damp. Your building seems plenty aerated and dry on three sides but maybe the back against the bushes is hold damp in the wall? Not sure what would work as a fix for that thought beside cutting out that section of the bushes. But might be worth checking how damp the wall is back there.

In my garden studio I open windows in summer. In winter, I run back to house and open the door enough times to let fresh air in. Not seen a bit of mould anywhere.

Comprehensive coverage and high grade workmanship as usual. Cheers Andy.

I built a simple wooden summer house with a basic felt roof which after many years still smelt of fresh pine. The key to keeping it fresh was to leave the windows open always for constant ventilation while not in use. We even had a bed in there for a while with no signs of mould or damp smell. No bugs either because of how dry it was. It did get the sun to be fair too. If I were you I’d just ventilate as much as you can while not in use for the mould issue and heat up as required

1:26 He wasnt kidding. Hear that door seal? I just ran a window A/C unit in mine.

Really appreciated this video. It gives a really good insight into getting fresh air into a studio room.

Very interesting Andy thank you.

I cant believe how good that sound proofing is wow

Great video, thanks. I've been looking into MVHR for my bathroom and kitchen, and have researched a bunch of options, most of which are between £500 and £2000 for a single room unit. I had (snobbishly) discounted the Kair, but am beginning to realise that, even though the design seems a bit basic (1990s, even), it seems to offer everything (and more) that most of the much more expensive units do.

Definitely vaguely useful, Andy. I thoroughly enjoy watching you and, as always, yes, let’s be nice to each other. Classical music too. Bonus 🌞

Been looking for a review for this thing for weeks, and today I stumbled across your video from now where. Great video.

Great video and you have also highlighted the need for ventilation in garden rooms. We built a a garden studio using a SIPS kit back in 2020 for my wife who is a hairdresser so potentially, lots of warm moist air. We air tested the completed studio and realised that even with a three panel bifold door system, it was pretty air tight so installed a mini MVHR by Blauberg Vento, similar price back then not so now. No mould and the ceramic core that captures the warm outgoing air is very effective.

Nice one Andy. We have a summer house with two opening windows (fanlights) which we leave on the ‘sneck’ all year round - no mould., it’s used as an artists studio. On the CO2 front, it’s quite pernicious in the sense in the early stages it can just cause you to fall to sleep - if you do in a rising CO2 situation then you are in the shit.

it is shocking when i got on my kneed and looked behind the kitchen units on the backing boards , especially by the under sink, so much black mould !!!, it creeps up on you without knowing for years

Well done ! Keep in mind to replace / clean the dust/insect filters regularly 3:18 I have a Vallox 90 SE central ventilation with enthalpic heat recovery (retaining some of the air moisture) and it indeed works both ways. In winter time I need to activate an electrical heating element for the fresh air intake to prevent freezing the heat recovery cell. Decentralised ventilation things (like yours) are kinda genius: first sucking warm air out warming up the filter package so when blowing outside air in it gets warmed/cooled. 7:48 at an event with Bosch personnel they told us that the front hand (here your left) must grab the handle from below (also when operating a drill with a kickback sensor) so when the drill is binding it is safer 25:42 you could extend the pipe on the outside. For the centralised units they have some add-on sub-terran heat recovery system that equalizes outside air temperature across seasons. But this adds a load on the ventilator. Cheers and enjoy your music room soon

Hi Andy, I’m a commercial gas engineer and in commercial kitchens we have to test co2 levels, the guidelines say that anything under 2800ppm is safe between 2800ppm-5000ppm is classed as at risk, over 5000ppm is dangerous. As far as I know co2 isn’t poisonous like CO (carbon monoxide) it just displaces oxygen. I’ve had my co2 tester. Just thought I’d share some knowledge, love the channel have been watching for years!

Nice tidy job. I have a well insulated very well sealed garden office and it can get stuffy in Winter when the windows are mostly closed. I try to change the air in the morning or evening by opening the windows for a bit, and I have a little 500 ml dehumidifier from Argos which I leave running overnight to prevent dampness from building up. No mildew etc after 2 years.

Just an FYI - we have to run a dehumidifier all summer in our finished basement during the summer to keep the humidity under 60% to keep any mould at bay.

We have silencers on the vacuum blowers in work which do very well in comparison to no silencers on the blower side. When you look at how they are made up as an addition. basically Stainless conduit with slots in with sound proofing surrounding it and another stainless conduit around all of that, keeping it in place and protecting it. Worth looking at and adapting. Best of luck

Might be good to add a secondary canopy over the outside vent to increase the long term waterproof integrity

I was involved in a practice room build very similar to yours minus the window, with a room within a room design. Brick outer leaf mineral wool filled cavity of 100mm, 63x38mm timber inner leaf with mass loaded vinyl glued between two layers of soundblock plasterboard with skim finish. For ventilation we used ducting in the wall with three "silencers" or attenuators similar to a car exhaust made up of a larger pipe (around 30mm larger than the duct) loosely packed with mineral wool held in place by a wire or perforated tube the same size as the ducting. With the ducting ending up about 8m+ long and the silencers in line it was very effective at stopping the noise from a 120db metal drummer at full tilt and as long as it was used mould and damp wasn't much of an issue. Bass traps in the corner improved the sound of the room a lot and I would recommend including them at all 90 degree corners.

You're keyboard plate made me chuckle 👍

Unless you don't heat this room relative humidity of the air which is sucked in will drop, as a coarse rule of thumb an increase in temperature of 5°C of the fresh air taken in will result in a 25% drop of its relative humidity. So if the outside temperature is 10°C and relative humidity 80% this air when brought into the room and heated to 15°C will then have a relative humidity of 60%. But a better and more precise approach is using a relative humidity chart, you can find these online. This is a quite nice SVHR, it does not like most of these units use a ceramic core to store heat, but has an actual heat exchanger. This means this unit continuously extracts stale are and replaces it with fresh air, those with a ceramic core can only do one of these at a time and the unit changes flow direction every few minutes. The big disadvantage of this is in a very well sealed room, like yours, it has to fight against a pressure difference as it either only wants to get air out or in, that hampers it's efficiency a lot. If using this type of SVHR it's advisable to have two of these running in tandem, both changing direction of airflow at the same time, this is done with the controller. The units can be in different rooms as long as they are not too far apart and there is a good air flow possible between the rooms, so doors must have a gap underneath or a vent must be installed in the door or wall between the rooms.

Great content.

Not sure how much insulation you've installed in the walls but I would think that the moisture output from even one person in the room for a couple of hours with next to no ventilation could potentially cause condensation on cool wall surfaces, giving rise to mould. Perhaps more likely with a fair bit of exertion when playing the drumkit. We have a timber framed garden office (built 2019 floor area approx 5m x 3m) in daily use with a Daikin mini-split ASHP, which helps control humidity. Insulation could be better, so not hermetically sealed like your studio, but complied with building standards at the time. Double-glazed with trickle vents but main air changes via normal foot traffic opening and closing sliding door. No condensation issues at all. Thanks for showcasing the Kair unit.

Great video.. I learnt a lot, and such a neat job as always 🙌might be nice when you make a surround.. making it look like a speaker or an amp.. just a thought😉 , cheers Rob

Nice project. If I may suggest, you should consider using or building an Exterior Fan Silencer and a sound-absorbing plenum chamber. This will help you reduce noise output through your ventilation while maintaining good ventilation. This helps me to silence my 115db air compresor in my living room workshop at my home almost to nothing. Good luck

You may need a dehumidifier !! I have one in my tiny flat,... (70m2)

Nearly got one of those in spring. Phoned them. Had brilliant advice - to hold on till we have a prolonged wet and rainy humid spell, maybe in autumn. If top of stairs to loft gets damp again and it's due to condensation. I'm now more likely to get their product

Very cool (or warm as the case may be). I have never seen a single room unit like that. I think I might have put the unit in the rear corner, but "heads or tails" is truly the ultimate unarguable arbiter. LOL Cheers, Andy!

Great video Andy. Have you thought about setting up a home assistant system? It integrates all smart plugs, relays and sensors etc. You could set up quite a smart setup for your studio ie, tracking co2 or humidity only whilst someone is in the room and then trigger the extractor or other items. Could also have warning triggers so if co2 gets above a certain level it could turn on a light or send a message to people's phones warning them to act. Can also set scenes with preset lights, sound etc Zigbee sensors are pretty cheap ~£10. It's all local and doesn't require cloud. Lots of options.

Drums!! Another good reason to locate unit on the window wall.

You thought about the ventilation issues months ago, and I'm relieved that you found a solution. Both CO2 and mold can have serious health consequences. It's surprising how well that simple unit dampens the transmission of sound.

That ventilation system is a very useful piece of kit.

Very cool room🤙🏽🤙🏽

Hi Andy Must admit I would have gone for the window wall , a possibly placed it at low level just above skirting height . As for CO2 levels that seem to have many in tis was , 400 ppm average out side and say indoor at a party up and over 1200 ppm . And if you’re a sub mariner you’re expected to cope between 6000/ 7000 ppm , and I believe astronauts are exposed to even higher values . But I assume they get conditioned to it , so maybe that’s the answer Andy you’re just going to have to live in the studio . 😂 No but seriously you’re absolutely right if nothing else you don’t want to be breathing in mould growth , and I would think you average sub with have very sophisticated equipment to manage such issues . And probably not a hole drilled to the outside 😀 . Great stuff as always 👍👍👍

Having fit hundreds of these fans, I can confirm that the control unit should not be fitted within 1 metre of the fan itself. Fitting closer, as you have, will lead to the fan itself preventing the control unit from accurately sensing the "real" humidity levels within the room. It's stated in the installation manual that comes with the unit.

Hi @GosforthHandyman had an idea for you to soundproof your vent. Use an old speaker with the back cut off so just the cabinet and speaker cover (decorative effect) full of soundproofing on a hinge or clips. Clipped on when recording taken off during general hooning... hope its a useful idea would certainly be in keeping with your rooms decor, please keep up the great content you have helped me loads. Thanks nr

Thanks.

Thanks for the content :) Any thought about underfloor cooling tubes like those used in earthships or a dual fan setup like in tiny homes? I'm not well versed in acoustic engineering, but would the most offending sounds in question (exiting through the floor), be more diffused upon their escape/absorption?

This is something you need to do DURING construction ...

Hi Andy, a great little project , for your music room. Fascinating some thing so simple that can do for your air quality ,looks simple to install, got it connected to a fuse spur I suppose a plug would be ok. as always a good video and very interesting ,Take care👍 Ps . Like the number plate on your keyboard😁

I’m struggling with the logic of mounting it facing the house, right above the drum kit? I would have imagined it better to go on the window wall facing the bottom of the garden? Nice bit of kit though and a decent price!

Weatherization people insulated my house with blown in insulation. As part of the project and because it's so tight now, they installed an air vent to pull out condensation and humidity in the house. It comes on for a timed period then automatically shuts off taking stale air out of the house.

Humidity is relative to the air temperature. The walmer the air the more water it can hold. So if you boost when its walmer inside mabe in the sunshine you will be heating up the air therfore reducing the humidity. Saves using a dehumidifier

Love your videos Andy, they always seem to tie up with something I've got to do at my place. Did you get a definite answer on whether this unit keeps a room cool in the summer? I've been considering one of these for the past year for a room in a very old cottage. The room is below road level, with no tanking and breathable lime plaster. I've got a dehumidifier in there at the moment, mainly for the summer when room humidity is worse when it's hotter outside and cooler in this room. Hopefully the small fan in this unit could defeat higher winds in the winter. Thanks again.

Could you get a dehumidifier that you can run in there while you're away/not recording?

I recently built a garden drum studio and was too worried about sound escaping to make any large holes so I buried a couple of 3 inch diameter flexible pipes with some high RPM mining fans attached (rated at 250 cubic ft per minute), one pushing air in and the other taking air out. Due to the small diameter of the pipe, the sound of air rushing through is rather loud and I have no heat recovery but it seems to work ok and not leak any sound. I have found that no matter what the weather is doing, it's always cold in the room due to the amount of concrete involved (i used a similar construction to you by the look of it, except for laying the outer layer of blocks flat and placing a 2 inch baton with insulation between inner blockwork and plasterboard) In my case the fans seem to make zero difference to the temperature of the room but at least if the music doesn't work out I could get into commercial meat storage

Useful cheers man. Couldn't help noticing your music stand content, great track fella, let the n'hitsuts hit the floor 😂

To help with soundproofing around the ventilator, you can hang sound absorbing acoustic panels near it which, I am told by those familiar with these things, should reduce the effect of problematic sound waves. Wall panels, hung rather like pictures, reduce reverberation by absorbing rather than reflecting sound waves depending on their NRC rating.

I saw on the HeatGeek channel recently, they wanted to see if they could enclose and how tightly their heat source pump. Apart from using there software/sensors etc to check effeciency internally etc they also used smoke bombs to see how the air flowed outside at the pump each time they made the enclosure smaller. The later may help identify size and shape to restrict the noise travel, well maybe.

The Kair unit, you picked seems to offer 10 litres/sec on "boost". So as no one is sleeping there overnight - it is likely to be enough, and should reduce the risk of mould, forming. The obvious way to kill common moulds is the use of a UV light source sun-light and or a "Black light" lamp, with lower humidity.

We have installed air con in a number of garden rooms. They dehumidify as part of the cooling process and also have a dehum mode. They heat in the winter and cool in the summer. A dehumidifier would prob be your best bet

I fitted a MHVR to a newbuild. Ventilation is always ignored and is vital for good health. It's a trade off for sound deadening. Retrofitting will always compromise your design of the building. I did make a 5*5 metre summer house, but it had vents and underfloor heating which never allowed the temperature to fall below 16C so dampness or mold was never a problem

I thought the air pushed back in was dehumidified as part of the heat transfer process..? This caused condensation, another reason for the slight tilt downwards.

I've got a garden room and fitted an air conditioning unit for cooling and heating.. for fresh air exchange ive got an inline ducted fan that supplies fresh outside air into the side of the air con unit which then heats or cools the outside air up.

I've just done the same, fitted an envirovent heatsava, doesnt seem to make much difference to the humidity but does help with being able to breathe. Maybe next step is a dehumidifier.

Hi Andy, another fine video. How do you size the unit? Just a gut feeling, but the size of this unit/heat exchanger looks a little small for the room size. I'm a great exponent of the saying "if it looks right it probably is".

You can baffle that vent, so that almost no sound gets through. I believe this is what you're discussing toward the end of the video.

Many years back, before the MHR stuff was common, I visited a home in Sweden that had gone a different route. They'd buried quite some length of ventilation duct (can't recall now if this was a combined passive intake and exhaust, or the two separate and powered by fans and laid next to each other, which would have been a crude heat exchanger) under the ground, doubled back on itself in tight hairpins, so it came into the house slowly and with the worst of the chill taken off by the depth (and possibly also by an exhaust). They said it was effective and it had been cheap for them. I imagine that several bends and earth above would go some way to attenuate noise too?

my mother had a garden room with double glazing but it had trickle vents , dont think she had any issues

I’ve got a studio with just a vocal booth built as a room within a room and didn’t put in ventilation for fear of the neighbours hearing me! After 2 years I’ll now make it a priority-mould and only being able to spend 20 minutes in there at a time the main reasons. Great video as always and given me food for thought. Also, could you have a removable cover for when you’re drumming/not drumming?

Interesting video - thanks. The CO2 thing is a bit of a red herring. Carbon monoxide is very dangerous, CO2 much less so. As an anaesthetist I often gave patients 5% (50,000 ppm) CO2 to get them breathing. The levels you are talking about will just cause an imperceptible increase in your breathing, as blood levels are tightly controlled by the brain. Above 5% it feels unpleasant (think swimming underwater) and at 10% it’s dangerous. As I see it your problem is mould which likes cool, damp environments. You need drier, warmer air. A dehumidifier will dehumidify a lot better than your device. A heater would warm the air and building, and decrease relative humidity. A bit of air movement is obviously a good thing too.

MVHR is brilliant.

Hi, I bought a vent axia HRF for my bathroom some years back, it was good for air circulation but the heat exchange wasn’t very good so it ended up just blowing into bathroom cold fresh air (in the winter months). Interested to know what yours is like on that front. Great channel by the way!

I have a garden room. I have trickle vents above the double doors and little window which I always leave open. I haven't seen any issues with mould

Interesting stuff, I tried an expensive MVHR in a bathroom and it died within a few months, lost interest after that. I did see a 6' version that looked fancy, may be one day. With your situation, and this is a faff, if you could add some more pipe externally that points the ground, then comes back up to 6', that might give you enough space to put some baffles and really drown out the sound bleed in/out the room. Of course it might not make the MVHR work as effectively I guess, it might even struggle sucking/blowing through that much pipe. Nice one for sharing. Built my outbuilding a year or so ago (I work in construction), just a skin of blockwork with 4' of external PIR mechanically fixed, then 4' on slab and 4' on warm deck roof. It's far from your acoustic levels I'm sure, but good enough for my purposes. Keep up the good work 👍

Hi Andy, how is this sytem holding up? Any concerns? I am looking at installing MVHR in my small garden room and thought this looked great after watching your video...

What was your Carbon dioxide levels after installing this unit?

I broke a metatarsal bone in my hand a few years ago, trying to drill rock for a retaining wall post.

had a boiler once that was leaking into the downstairs space didnt know back then but I crashed on settee could not make it upstairs I just crashed and boy did I feel so groggy...about 6 months later showed a boiler engineer mate and he said the soot shows its leaking.... fixed it and no more groggy...not drowning just TIRED hard to rouse...

That room no longer meets the PercussiveHaus standard....

Fantastic video, I'm about to embark on a new build bungalow, and was really curious about these single use units, it's small with only 5 seperated areas so thinking 5 of these would be cheaper than a full mvhr unit. But last time I checked I couldn't find many variations of these single use units for sale so didn't think they would be up to much but you've perked my curiosity again!

@gosforthhandyman how has the vent been working thus far? Great video.

On humidity and ventilation you have to really think carefully about absolute (g/m3) humidity versus % relative humidity., You could have 10 degrees outside 80% humidity, 20 degrees inside 60% humidity - the air outside would have significantly less water in it by volume, so if you're bringing that in and warming it to the temp of the room you're going to be reducing the relative and absolute humidity inside. When I bought my house it came with a PIV system stuck in the loft and on all the time and I have temp/humidity sensors in every room and now the PIV system is on a smart (zigbee) plug and I actually run calculations of how much absolute humidity is in the air in the immediate vicinity of the PIV outlet, the house as an average, and at the inlet of the PIV system and temps and it makes smarter decisions about when to turn on and when not to so I don't pull in more moist air, don't pull in air that's too hot or too cold etc, which is far far better. You're not actually supposed to do this with a PIV system, but I simply don't care because it's miles better at doing the job. Eventually I actually want a whole-house MHVR system, but that's a big expensive job for the future. Anyway, the point is absolute humidity inside and outside is more important than the relative humidity when you're going to be warming that air up; if it's lower absolute but higher relative outside it's still worth pulling inside because the end result is less water.

Do you have trickle vents on your window? Usually that's enough for garden rooms

mad that you didnt point it towards the river

if you don't want mould then the humidity probably should be 60% or lower. Allowing it to run through the night probably means it doesn't need to work as hard during the day?

Great vid mate. I'm building my first woodworking workshop this year and wonder if this would help maintain humidity levels in there around 50% to minimise timber shifting, etc. How do you reckon it would fare with fine dust in the air?

Does it have a condensate drain?

For diamond core: my big DeWalt SDS couldn't do 117mm, let alone 150mm, tbf it's had a lot of use and probably needs new brushes. Got a Makita diamond core drill - perfect up to l50+mm. Makita have kept up quality of old product corded tools; DeWalt old product corded quality has plummeted. Proper dcd gives controllable torque for large holes

Well Andy, that's a bit disappointing on the sound transmission front, but it's definitely better than drowning so what do you do ! I'll be interested to see what you come up with to mitigate and also to hear how it is for incoming noise too !

Most people install AC in the garden. Rooms the units are both heat and cool and also have hymidity control. This could be a good option for your room

I am not likely to need to do this anytime soon, but still, so many delightful details here. Multitools to the rescue (again)! And that license plate over the keyboard 🤣 Also, as someone from Southern California (who now lives in the UK), I'm amused by your shirt touting San Francisco as a place of "Endless Beach". I assume it's meant to be ironic 😂😂 to be worn as the first of four layers whilst shivering too hard to hold a skewer over the bonfire at a bay area beach in June. Also also, excellent music; the starting off with the drum solo made me think that (just you on the drums?) would be nice as background sometimes too! Plus I enjoyed the classical music. I hope you'll forgive a minor rant, but I'm so tired of the DIY channels with men as hosts who blast hard rock/metal music every. single. time they're doing a work montage. Extreme compensating-for-something vibes 😅 (funnily enough, they're all American...)

Look at dorade boxes. You can then make the inside walls complicated for soundwaves to travel,, but won't affect air flow

Any reason why you stopped and started tackling it from outside? Could have just kept going from inside and then jigsawed the ceder.

i wonder if u can build a dampening box over it on the outside , that allows airflow of course , but its not directional ( in the same line ) and its also extremely padded out with sound foam

Thing is with the humidity is like you said, the mould effects the room not so much the person. Best to set it to 60 and let it run on boost until it gets on top of the humidity issue in the room.

Plug in a dehumidifier beforehand? Switch off the ventilation unit before going to bed?

I assume the fan works in reverse when pulling fresh air from outside? It's not pulling in fresh air when it's pushing air from inside? Won't that create a negative pressure in the space, since it's not that large? Or is it such a low volume of air being pushed and pulled that it's not noticable? If it does, then air will find it's way through all small gaps.

The Humidity setting on the device is intended to achieve the desired humidity in the room. Condensation occurs on the heat exchange plates that you showed in the clip. This condensation then drips out through the internal pipe with the 5mm problem that you tried to seal. Setting the humidity at 80% will not prevent or stop the mould, it will only make it worse when you yourself are in the room or drawing humidity inside from a higher outside % when in "standby mode". The WHO recon between 50-65% humidity is a healthy environment. I suffer from high humidity. I have installed a loft MVHR (£1000) that services the house via ducts, and use a portable 20L Pro-Breeze (£200) at the central inlet defuser. The setup maintains my home at about 63%