MJNewton

Have you considered just using an inline extractor fan for this test? It ought to give the same result (I'd say you only need to emulate the supply side) but would do so without the commitment of a full MVHR unit.

Is the extract-only mode desired because of the potential smoke issue? If so, are you sure it'll work as expected? For any air to be extracted there obviously has to be an equivalent amount of air sucked in hence won't the smoke outside still be a problem? I suppose there will be a difference between air coming in via gaps in the building fabric versus all from a single inlet but whether that will help I am not so sure!

Thanks everyone. I think I may as well go for the cheaper of the two (Domus)... 'Look after the pennies...' and all that!

By all accounts it seems that dimensionally all 75mm OD semi-rigid ducting is equivalent (or close enough perhaps?) and that mixing components from different manufacturers is therefore possible but does anyone know if there are any other differences in materials, quality etc of the pipes? What made me wonder is that one well-known supplier sells both Domus and Airflow ducting and the price for a 50m roll of each is £142 and £168 respectively. Perhaps it can just be explained by variations in the supply chain and other retail issues? I was going to ask said supplier but they are closed over the weekend and I can't seem to settle with unanswered questions hanging over me! ?

Have you considered the Timeguard TGBT4? Looks quite 'modern' I think and well suited to an MVHR installation (I always think Horstmann's sometimes look a bit old school! ;-)) £20 from TLC.

Unfortunately for me this *is* afterwards! ? (in terms of it being a retrofit anyway). That said, the process of pulling through the ducting means it's a good opportunity to pull some cables through with them so, yes, it is definitely something to think about in advance.

Lots of options... thank you. What I might do is keep an open mind and try a few different strategies. I do enjoy the engineering aspects of designing and experimenting with things like this and so the journey should be as worthwhile as the end result.

Thanks everyone you the input. Perhaps a timed boost would be more reliable as I don't want to be trapped in a boost just because some turn-off threshold hasn't quite been reached. As you said, some monitoring of our system and how it and the house reacts should give more of an idea of what is required. Yes, I like the idea of that. I've noticed what little effect opening windows has on very calm nights when it's hot inside and yet the outside air temperature is cool. Hopefully the MVHR will be able to at least get some air moving. I've found that with quite a few units, and yet others are full of really useful information. I can't be the only one whose buying decisions are heavily influenced by the presence (or lack) of such detail. To be fair to Titon whilst their installation manual simply said the summer bypass was 'automatically controlled' (and nothing more than that!) I got in touch with them and received a very helpful reply from their technical department explaining the control strategy and openly inviting any other questions about such details. Understandable. What I might actually do is run cables with some of the ducting runs so that I can add on, perhaps in parallel, some manual controls should I conclude that they will serve us better. Truth be told though, I'll quite happily (and consistently) manually trigger the boost function prior to showering but I'm not so sure I can depend on my wife doing the same (and perhaps daughter too when she's old enough - she's only 1 though so still plenty of time for training!).

I suppose every house/layout is different, and indeed we all might have slightly different priorities and preferences over what matters most. I know what you mean about the putting plans into action. I'm sure when it's all done I'll have spent more time planning than doing, and that's despite mine being a retrofit which throws up challenges all of itself!

Having picked up a Titon HRV1.25Q Plus Eco for a price that was too good to pass on I now find myself with slightly less controllability than the Xpelair Natural Air 180 unit previously planned for. Specifically, the Titon's humidity-controlled boost function is based on an absolute threshold rather than rate-of-rise, and its summer bypass has fixed thresholds that cannot be adjusted at all. All along I have been planning on employing a Pi Zero to monitor system temperatures and control boost and setback flows, and so I have decided now to bring humidity-controlled boost and summer bypass within its scope also. The former can piggyback the existing boost input but with the bypass being internally controlled I have had to pinpoint on the control PCB where to tap into to influence (actually take over) this function. What I would like the panel's input on is the control logic for these features in case there's something I haven't considered (or just got plain wrong!). Humidity-Controlled Boost I am attracted to rate-of-rise control on the assumption that it'll ride out seasonal variations better whilst also being more sensitive and reactive to genuine need. To achieve this control I think I need to consider: Inputs: Extract (i.e. from rooms) humidity Outputs: Boost Settings: Rate-of-rise threshold ($rateofrise), time period ($timeperiod), when to turn off again ($deactivatethreshold) Control Logic: 1) If the humidity rise over $timeperiod exceeds $rateofrise activate the boost. 2) Continue with boost until the humidity falls to $deactivatethreshold. This sounds reasonable I think? What should $deactivatethreshold be though? The pre-rise humidity value, or at least something near it in case the background humidity has risen slightly in the meantime? My starting figures are likely to be something like 5% for $rateofrise and 5 minutes for $timeperiod. Incidentally, I was planning on taking measurement every five minutes so that'll be the minimum boost time period. Summer Bypass From what I have read it seems that summer bypass works better in theory than in practice but I like the idea of it and given the Titon has the capability I may as well make use it. As per the previous process I think I need to consider: Inputs: Extract (i.e. from rooms) temperature, Intake (i.e. from outside) temperature, time of day(?) Outputs: Summer bypass, boost(?) Settings: Room temperature threshold ($roomtempthreshold), Outside temperature minimum ($outsidetempmin), quiet time ($quiettime), when to disable bypass again ($deactivatethreshold) Control Logic: 1) If the temperature of the air being extracted from the rooms exceeds $roomtempthreshold and the outside temperature is at least $outsidetempmin then activate the summer bypass (unless the outside temperature exceeds the room temperature). 2) Additionally (and optionally?), with the bypass active also activate boost unless we are within $quiettime (e.g. at night). 3) Continue with the bypass active (and, optionally, boost) until the room temperature falls below the $deactivatethreshold. Typical figures might be 22C for $roomtempthreshold, 15C for $outsidetempmin, 2300-0700 for $quiettime and 18C for $deactivatethreshold. Thanks for reading this far. Should I be considering a different approaches? Is there anything I should/could consider?

Not the most popular posts this one! ? Nevertheless, I thought I'd follow up with my conclusion in case it is food for thought for others that may find themselves in a similar quandary. What I have decided to do is *not* put a vent at the top of the top stairwell. The reason being is that my planned flow rates (on boost) for the top floor are: en suite extract 8 L/s, master bedroom and dressing room supplies 5.8 L/s each. Thus, there should be a net positive supply (11.6 compared with 6) which should therefore result in air flow out through the stairwell thus in turn eliminate the dead spot I was concerned about. Of course, this theory is wonderfully simplistic but it's all I can go on until the system is installed at which point I could always add a vent if need be or, most likely, just live happily with the as-planned system!

I'm a bit confused about this bit. Whilst supply and extract complement each other functionally they nevertheless operate completely independently with their own fan and air ways. I would therefore not expect adhustment of a supply vent to change the noise levels heard from an extract vent. Perhaps though, the fact this is happening is a big clue as to what the issue might be? (Not sure what though!) Incidentally, have I understood you correctly that there is only a single supply and extract vent at the moment? If so, it could well be that the minimum speed of the unit is still far exceeding the airflow that you want/need passing through the vents. An anemometer would be useful, and will be required anyway come balancing time.

Great - thank you.

Thanks everyone for the replies. I did spot some isolation hangers like the following: ..but they seemed surprisingly pricey and not all that readily available. I'll look to make a DIY equivalent with whatever I can lay my hands on, perhaps exhaust hangers as some have mentioned. For isolating the unit from the ductwork I believe semi-rigid aluminium ducting like that below is what's generally used and so presumably is flexible enough to perform this function well? Is there any issue siting this so that it acts as right-angle bend between the MVHR unit and the ducting? Or am I better using a solid (smooth) right-angle bend and then using a short length of the semi-rigid to connect straight with the ducting? I might be over-thinking things and it really doesn't matter either way...

Ah I see. Finger's crossed it is primarily the fact that it is running unpiped. I am sure that others that have installed MVHR units have run them prior to installation (I know I will be - I won't be able to help but fire it up!) and so should be able to comment about this. I see that inline silencers/attenuators only cost tens of pounds and so that could be worthwhile as a matter of course anyway. What unit have you got?