MJNewton

I retrofitted MVHR into a 3-storey 2007 developer-built house and whilst it was doable it was hard work as I didn't want any visible boxing in! I was lucky in that the house uses I-joists which happen to all run the right way (I had to go through one but that wasn't too difficult), the top floor has a dressing room and walk-in wardrobes so was easy to run pipes from the loft-mounted unit down into the lower floors, and I was extending the ground floor so ripped the ceilings out to make ducting (and everything else) easier. We've now removed the extractor fans, foamed up the trickle vents and haven't looked back - it's superb and would highly recommend it if you're prepared for the sleepless nights planning ducting routes.

If the extract fan isn't running howcome you can feel a strong flow out of the external exhaust vent?

Have you checked the right ducts are connected to the right ports on the unit? All too easy to make a mistake with the supply/extract/intake/exhaust nomenclature. Even more confusing when symbols are use instead!

I don't know if I dare admit it but we've got a Persimmon house (built 2007) and it's constructed very well. I've seen practically every nook and cranny having worked on it, extended it and retrofitted MVHR. I'd like to think I understand a fair bit about house construction and techniques having renovated a few properties over the years covering practically every aspect so I don't think I've got a warped sense of what's good and bad. It was a show home though, so perhaps as mentioned there might be something in that. That said, I've also noticed that every show home we go in these days (my wife's a big fan of noseying around these things) always disappoints us in terms of size and layout, and in some cases construction, so perhaps there's something else behind why ours seems fine. I'd never defend Persimmon based on what I've heard about them, but I'd certainly defend and give them due credit for this particular house they've built.

It wasn't so much the user manuals, I thought they might have design guides. I'll have a look later.

Indeed, but the reason the specific model is worthwhile knowing as manufacturer instructions generally override general regulations and so really cannot be ignored if they say where vents should be sited (noting that the regs are silent on the subject).

Absolutely, and I wasn't judging. Indeed I'd be lying if I said similar thoughts wouldn't cross my own mind, even if I subsequently ruled them out as 'tempting but not quite right'!

It's up to you but you've got to live with yourself and I'd always play with a straight bat when it comes to issues of honesty. What goes around comes around and all that. At least you've got a slight chance of seeking a remedy here, whereas your buyer wouldn't have any (unless they tried to persue you of course!).

I try and remind myself of that whenever I fail to do something perfectly or, worse still, a tradesman I'm paying for does instead! I also try and remember there are a million other houses out there with less-than-perfect aspects to them and they somehow find a way to live a perfectly functional life without losing sleep.. ?

Yes, I was thinking plaster too. The green might be a result of flux on the plumbers hands during installation. If you clean it up and tape a sandwich bag around it you'll soon find out if anything's coming out.

Aree you sure that's a leak? I wasn't sure it necessarily looks like one given where the white stuff is/isn't. Obviously clean it up and see if it comes back.. Automatic air vents can often be sealed closed but your cap looks like it's got a hole so it might not be possible.

Yes, but not usually that deep so could be emptied in the right (wrong) circumstances. The sewer smells would still be contained though (or rather would be blown out of the flue, via the burner!).

I don't think there are building regs related to room vent locations, however I would imagine the manufacturer of the fan unit has design guides that cover the subject and it'd be hard to argue against them. What make is it?

Okay, thanks, will give it a go. I've got some needle files. Gulp.

Okay thanks. Just to confirm, this stuff? I notice it mentions static cracks and doesn't specifically mention flexible which seems necessary in this instance if it's going to keep moving with the seasons? Point noted about opening the crack up. When you said it previously my heart sank as I knew it'd feel wrong when it comes to doing it but deep down I'd know (or at least hope!) it's right.

I never did get round to sorting these cracks out but I've got interested in them again as last week I noticed they were much more visible ('blacker') and assumed they'd got worse... Today however they're practically invisible. The difference I'm sure is down to the -5C of last week and +9C today. If there's temperature-related expansion/contraction going on (noting it's a timber flat roof with a large opening so plenty of potential for movement) then hard filler/plaster is likely to be unsuccessful. @nodyou mentioned 'good quality flexible filler' - is there anything in paeticular you had in mind? It's a minefield out there with too many choices... Edit: I'm not necessarily after 'invisible', there's just something about a black crack that kind of says 'falling down' to me; they just seem particularly unsightly against an otherwise perfectly smooth and bright white ceiling and whilst you can't see it from all angles the sofa just happens to be the prime viewing location...

I only intended it to be a joke..

What's the setting actually a measure of? The reason I ask is that on my unit it can't be adjusted (not even visible) but it's never kicked in despite the outside temperature regularly sitting at -4C. I've put this down to the fact that the exhaust air in those situations has been, say, +6C and so the heat exchanger itself is still sitting above zero hence not at risk of frosting up.

Oh okay - good! I thought I'd come up with an idea that would revolutionise the world of MVHR. Hopefully still time to cancel my patent application...

Our Titon MVHR unit has a 'setback' feature whereby, if you apply 240V to one of its input it'll reduce the flow+extract rate to halfway between minimum and the 'normal' rate. I believe it is intended to be used when away from the property however I was wondering if it could find utility overnight? The system works really well and isn't noisy, however I am mindful that in our less-than-optimum house (in terms of insulation, airtightness) it could be advantageous to reduce operating losses whereever possible and whilst it might be a compromise on performance to do this during the day I figured at night our water-producing activities are much reduced? Sure, we're still breathing but we're not bathing, cooking etc and we'd still be getting some level of ventilation. Just thought I'd share the idea with the panel and see what you think. I already control the unit with a Pi and some 'smart' relays so adding another input wouldn't be too difficult, and I suppose in addition to limiting it to nighttime I could activate the setback only when outside temperatures are particularly low and corresponding heat loss high.

I'm not religious but I must admit I'm tempted to start praying for his return.

Now that I've said this I decided to be brave and go back to page 1 and found that it only actually started in September 2020! The infamous 'Covid-19/All things Coronavirus' thread, started back in January 2020, is now at 353 pages. A quick comparison reveals that Zoot's extension has created over a quarter of the posts in half the time which is really quite remarkable for one of the most significant and contentious global events in modern history (the pandemic, not the extension...). Here's hoping the vaccines continue to work against more than just what they were originally designed for.

I don't dare go back to page 1 to check but given we're on page 79 then, yes, an early-90s start date sounds about right.

If you've lost the plot I'm afraid you'll have to go back to the beginning. Don't worry about missing out though; we'll still all be here.

Could well be, and intended to represent the 'ambient' temperature of the surroundings. 5.9°C sounds reasonable for a cold roof space with an outside temperature of 3.4°C. (Mine is currently 4.1°C in the loft, 1.3°C outside so broadly similar) With a supply:extract ratio of 13.1°C:17.8°C that gives a 74% heat recovery efficiency which whilst on the low side is still within the realms of what might expect, particularly if the flow is on the high side (harder to recover the heat) and the loft is cold. Tweaking the flow down a bit and adding some insulation to the unit might help. Also, make sure any ducting in the loft is insulated too - I imagine your house isn't actually at 17.8°C, particularly at ceiling level, and so there's some heat loss along the way in the extract ducting. All very common for a retrofit in my view. Incidentally, whilst it'd be worth experimenting to see if you can up the efficiency do remind yourself that even 13.1°C is considerably better than the 3.4°C that you'd have coming through window trickle vents that you otherwise should have!