MJNewton

That could well be it - the 'decent standard' may well have resulted in less natural background ventilation in that room. Completely disagree with you their Zoot. Behind that question lies the answer to your problem. There's no magic going on here - it's just scientific laws being followed and whilst you might want to believe they don't apply to your part of the world I'm afraid there's no escaping the fact that they do.

I wasn't suggesting Velux as such, but would be expecting 100% blackout from whoever/wherever I did buy one from.

I haven't personally experienced flat rooflight blackout blinds but for what it's worth I did once have a blackout blind in a Velux window and it never ceased to amaze me how perfect it was. Regularly I would open it in the morning and be really quite shocked going from absolute pitch black to daylight. I'm assuming ones for flat rooflights would be just as effective as it's the side rails required to defeat gravity that is the key to their success.

If you're not quite sure - or just what to keep costs as low as possible - keep en eye on eBay as MVHR units often come up for sale at half retail price or less. Many are brand new or at least 'as new' but might be missing packaging etc and without warranty. There's definitely money to be saved. Mine had been fitted but never used, as part of a development of multiple houses but they hadn't met the spec so they were all ripped out and replaced with the next size up. The bloke doing the reinstall action stuck them all on eBay for just a few hundred each. I reckon I'd still get the manufacturers warranty as the serial plate is date stamped so I could easily claim it was fitted prior to me moving in hence no receipt.

Yes, thanks for this. We've got a Titon MVHR which uses ebm-papst fans and so chances are there are a number of other units that also do.

It gives you a baseline. When the condensation returns you can compare the readings and see what's different - higher RH? Lower internal temp? Lower external temp?

It could fall under the general requirement of: 134.1.1 ERECTION AND INITIAL VERIFICATION OF ELECTRICAL INSTALLATIONS Good workmanship by one or more skilled or instructed persons and proper materials shall be used in the erection of the electrical installation. The installation of electrical equipment shall take account of manufacturers' instructions. If the manufacturers' instructions say that you should fit an isolator then I suppose it's just down to you to justify not taking them into account? The circumstances might dictate the signifance of having to do so eg there might need to be a particularly strong reason if someone broke their neck falling off a stepladder because they were trying to clean/unblock the fan in the dark as their only means of isolation was via the circuit breaker of the lighting circuit it was attached to.

I'm confused. You brought the subject of condensation (and it being a problem) up, not us.

Yes, several times now. Zoot won't listen though as he lives in his own little world (by his own admission). I'm wondering why the issue was even raised as it is apparently unfixable because the usual laws of science don't apply.

Damn - no delete. I was trying to make a joke there but reading it back I'm not sure what my joke actually was, and it's certainly not making me laugh. Move along, nothing to see here.... Back to Zoot's pants please.

1 100 ?

Wow, okay, sounds pretty unique. Probably not something I can really help with. Oh, and your humidity meter is faulty.

Now that's not *too* bad (you certainly aren't living in a rainforest despite what your pants might be telling you) with a dew point of 11.5°C, but then I imagine you don't yet have condensation forming - that'll occur overnight as both the internal and external temperatures drop. A dehumidifier would definitely help (reducing the RH to 50% @17.5°C would give a dew point of 7°C so very low) as would ventilation (if we assume the outside temp is now 4°C and 99% RH, bringing that air in and heating it to 17.5°C would give a RH of only 43%).

Book us all on - we'll get a bulk discount. I'll print the thread out and bring it with me. It'll help them help us if they knew what we've been through.

Okay, that's useful. For that temp and RH the dew point is 13.2°C i.e. water will condense out of the air on any surface that's below this temperature. Noting how cold it is getting outside at the moment I could imagine this being quite possible at the bottom of your doors, particularly if there's not much air movement within the room.

Forgive me Zoot but you said something similar about your radiators saying beimg 'hot' to the touch but it turns out they were 40C when actually measured. You were right in a sense, but also wrong given the issue at hand. I'm just interested in figures really. ? Okay, that helps, but honestly - figures would be even better.

You definitely can prove it - temperature and humidity readings inside and outside will show whether you're living in a rainforest or not, and from that you'll/we'll be able to work out what you might be able to do about. Don't be so quick to give up.

Personally I think it has some relevance but is more of a red herring. Like your carpet underlay debacle, I suspect you'd likely find that the frames and units are actually similar/same as those fitted to millions of houses (like mine) across the country, many of which don't suffer condensation issues (again, like mine). Heat loss, and by extension, surface temperature of windows/whatever is important but you should be focussing more on improving heating and ventilation whilst reducing the creation of water vapour to begin with as they are all within your direct control.

I wouldn't be focusing on the frames - I suspect you've got a temperature/humidity/ventilation issue. What's the temperature and humidity in that room like? Last thing at night and first thing in the morning when you discover the condensation would be the ideal measurement times. Middle of the room measurement, not near any wall/ceiling/door.

My preference for a 'real' outside temperature was just an issue of accuracy as my nearest weather station is around 10 miles away and any discrepancies could really throw out my calculations of heat exchanger efficiency/performance.

Basically, given you've got different duct lengths and rooms with different flow rate requirements (eg large rooms vs small rooms, kitchens vs bathrooms vs en suites etc) then you need to 'balance' the flow rate to each vent to give that which is desired. It's not too dissimilar to balancing radiators but instead of throttling the lockshield valves you throttling the ducts by either screwing/unscrewing the outlet plate or, increasingly common, putting in restrictor rings inside the ducts where they join the manifold (the bit where it branches out from a single large duct to the smaller individual room ducts). The latter can be a bit trickier (opening up the ductwork, swapping rings in and out) but does mean reducing a potential source of noise (throttling airflow increases noise) by doing it well away from the rooms. There's loads of information about, but have a start with this thread:

I don't, but I'm wondering if they are overplaying the noise issue somewhat? My unit is nothing fancy (Titon HRV1.25 Q Plus) and I don't have any issues whatsoever with noise. It is mounted on the gable wall in the loft of a 2007 Persimmon-house which aren't known for great noise blocking construction. It sits on some old exhaust hanger rubbers which likely helps. Attenuation of the ducts (for balancing) is done at the manifold (unit) end rather than at the ceiling vents so that may help somewhat at the rooms end. Certainly we don't hear anything in the rooms apart from when boosting but that's not intrusive by any stretch (just airflow; no fan noise or anything) and believe me my wife would make it known if it was! ?

(I forgot to add...) ... as a rate-of-rise humidity sensor so it boosts on a >5% rise in 5 minutes.

I added a Pi-based controller as I was finding the built-in humidity trigger to be a bit hit and miss. The threshold was set on the unit but it was an absolute threshold so just when I got the balance right it'd need tweaking as the seasons changed. Sometimes it wouldn't trigger when I expected it to and sometimes it'd do so when I didn't. As I had an unused Pi Zero and humidity sensor I put it to use even if it was a bit overkill. To lessen this though I add temperature sensors to the four main ducts so I could monitor (and graph) its performance. Useful to begin with when I was still learning about MVHR, and I still look at it occasionally now. Handy for knowing the outside temperature too, and I've always liked graphs. ? I may expand it to have greater control over the summer bypass and summer boost if I get some time to do so.

Great to hear the heat now appears to be coming through, but another slap of frustration given that the suggestion to disable weather compensation was made back in November. If that'd been followed we might well have all been saved from 40-odd pages of toing and froing since, not to mention given Zoot a warmer Christmas. Sigh.