Jolo

Yes, those ribbed sections are 1cm apart, so you can cut it to length. I ended up doing this all over, with good results! I even used one of the off-cuts to extend another section where I needed a longer section, joined with a regular metal-with-rubber-rings piece, as the 125mm plastic pieces fit together perfectly with the 125mm spiral ducting pieces.

You're welcome, @Mattg4321, I'm glad I was able to help Like you I was also disappointed that expensive solid attenuator I bought didn't seem to make a difference. I wasn't entirely surprised though, as the drone always sounded like it was coming from inside the green pipes, at it had the same reverberating timbre as can be heard if you speak into them. Yes I used 90mm ducting (external diameter) so the 100mm flexible silencer fitted over pretty nicely. The difference is amazing. Glad this solution worked for you too! (BTW if anyone else needs one, this is the silencer I bought, on the UK sibling site of the place I bought mine from: https://www.ventilationland.co.uk/en_GB/p/flexible-silencer-non-woven-with-connection-diameter-100-mm-length-1000mm/6172/ )

I might try this, though I'm not sure if it will hurry Brink up at all. I feel like I've dotted every i and crossed every t, and asked here and elsewhere to test my sanity!

Exactly right @Russdl and @JohnMo! I've gotten a template letter from the government's consumer authority, and I'm going to send it shortly. It gives them two weeks to repair or replace it, and if that doesn't happen then I can terminate the purchase agreement unilaterally and they have to give me the money back. I'd really prefer that it didn't have to come to this, but I don't see any other option as nothing is happening.

Yeah it's a weird design, isn't it? I'm sure I saw a bracket at one point, into which those flat bits at the top would slide. But I can't find it now. Maybe I dreamt it? Anyway, I just drilled holes in the flat bits! Also strange that the two-duct valve adaptors have sensible screw points. There's a new design which is even better, as it has a pair of screw points at the top and the bottom of the main section. Are you aware of the restrictor rings they sell, which click into the distribution box? https://www.ubbink.com/gb/products/ventilation/air-excellent-ventilation-ductwork/distribution-boxes/air-excellent-dbox-internal-air-restrictor-ring/ I used the Ubbink AerFlux online tool, and I have to say it made setting the flow up really easy, as it tells you how each ring should be configured. https://www.ubbink.com/int/advice-service/aerflux-configurator/ Although I don't know if it takes the UK building regulations into account, it definitely has the Dutch ones, which may be slightly different. VentilationLand seems to be an auto-translated version of the Dutch site https://www.ventilatieland.nl/ -- alhough it's possible that the Dutch site is an auto-translation of the German https://www.lueftungsland.de/ ! I'm not sure how it all ties together. I'm not sure how these companies work behind the scenes, it's possible that VentilationLand has to wait for a big delivery from Brink. But then some other similar sites don't seem to hold any stock of their own, instead the goods arrive from other retailers/warehouses (even though the price may be cheaper than on the other sellers' own websites!).

Thanks for the replies -- but just to be clear, it's definitely not the internal ducting, as I've mentioned earlier we've done every check possible. The extract ducts suck and the supply ducts blow. The ducting is still visible so it's easy to follow each pipe to its destination vent. We've tested with just a single pipe connected to each port on top of the MVHR unit, eliminating the internal ductwork entirely. It's definitely not external cross-flow either: We followed the supplier's guidelines, he's happy with our inlet and exhaust locations The bloke from Brink was satisfied with them The odour transfer is too strong and immediate to be happening outside anyway So the problem is definitely inside the unit, there is no doubt about that. However, my question this time was just about what the humidity should be for an MVHR unit that was working properly. Thank you John, that's good to know! Thanks Mike, that's useful information. But nothing changes regardless of the speed, because the unit is just blowing a mixture of fresh and stale air into the house. So when showering, the bedrooms and living room are getting some of the steam blown in. Not yet! This is one of the reasons I'm getting annoyed with Brink, they go weeks without any progress or updates. (Also, the odour transfer is so strong that anyone with half a nose can detect the issue. Spray a bit of deodorant in the bathroom and a few seconds later it arrives in the living room.) I'm now considering starting to send legally valid complaints to the supplier, in the hope that he'll get Brink to up their game. It's been three weeks since I let them know that the new exchanger didn't fix the problem.

Update... there is no update! I'm a bit disappointed with Brink and the supplier, to be honest. I don't get any progress unless I push for it, and there seems to be no answers forthcoming. The latest "news" is that it's been passed to the R&D department to figure out what might be causing the issue. One question for those with experience of such systems -- should the MVHR system help regulate the moisture inside the house? I ask because we've had really high moisture levels indoors, like 80 - 90% RH sometimes, which is surprising to me. Windows covered in condensation in the morning, even though we're running the unit at around 0.45ach. We're not doing anything weird like hour-long showers or running a commercial kitchen! I've taken to opening the window vents, which helps a lot with the humidity but of course defeats the purpose of the whole MVHR system!

Oops, I missed your reply somehow! It's a radial system. Small house, really simple, the ducting is mostly still visible so it's all been checked a dozen times. We've even tested it with just an elbow and a metre or two of ducting on the extract and supply ports, and the problem still exists, so it's definitely not a problem with the internal ducting.

Oh 100% Here's a photo from during our installation

Thank you @Mike that's useful info! I discovered last night that despite my best attempts to cover the metal box, some condensation is forming in awkward to cover places, so I might take the plunge and get a proper one. I do like DIYing stuff, but with the time and money I've spent on trying to insulate a metal box, I could have gotten the proper one!

Can I ask where you bought that, Mike? I wanted something already insulated, but couldn't find where to buy one! Ended up using a metal one and covering it in Armaflex, which does work but it was a faff

Yeah it's a bit confusing! Easy to read them as directional, which they're not. Just imagine the main unit in the loft of the little house, and it makes a bit more sense. Regarding brands, they're also sold in Germany by Wolf (also owned by Ariston) as the CWL-2. Knowing the various names helps when comparing prices on filters etc! Well I'm glad it's not just us DIYers who have to think carefully about it!

Sounds pretty idyllic! (Though I'm surprised you don't get a lot of flies in the filter) I only just had enough space -- I hadn't planned to add a pre-filter, so luckily there was a gap big enough between two other ducts to fit the box in. If the gap was a few centimetres narrower I couldn't have done it!

I'm surprised that ventilation systems don't come with a pre-filter like this, really -- or at least, that the're not more common. Sure, the unit has a filter inside it, but on mine this comes after the temperature sensor and the pre-heater, meaning that these components get covered in dust, and probably flies too. Also it's nice to protect the fancy expensive fine filter with a cheaper one!

@JohnMo Thanks, and yep we crossed off 1, 2 and 3 already, this was pretty much my thinking process when the problem occurred. I'll let the supplier decide whether to try a regular exchanger, but as I mentioned I'm sure it's not that, as the odours transfer even when the extract air isn't flowing through the exchanger. So it can only be number 4 (which is also my conclusion) and as you say, not something I can fix myself, it's for Brink or the supplier to do.