Barnacles

I've spent the day looking at various options and concluded that MVHR is the way to go. The layout doesn't really lend itself to PIV, I did almost plump for a dMVHR (as much to make my life easier on the install as anything!) but then in the end I figured I that MVHR is the "belt and braces" approach which will hopefully tick all the right boxes. I have quite a few bits and piece left over from previous MVHR and A/C installs so I can save money on the overall spend and I found a Nuaire unit for £699. Along with the other bits I need to buy I should be able to bring it in under £850 or so and I'm happy to fit it myself as it's relatively easy to work in the loft space. It's still more than I wanted to spend initially but if it cuts down on the maintenance and keeps the place fresh it's got to be a winner. Many thanks for all the suggestions and advice they're very much appreciated.

Hmmm, that's a different way to come at it, interesting. There is a bog-standard humidity controlled extractor fan in the bathroom already but with all the cold surfaces in there it's just doesn't cut it, we still end up with pools of water on the window sills (also stone!!). Insulating the walls would likely be impractical due to the amount of space we'd lose. My only concern with a dehumidifier would be the noise. I haven't used one for about 20 years but the one we had was really noisy, have they got any quieter in recent years? You're spot-on Mike2016, people don't open windows etc. What ever solution I go for has to be fully automated and tamper proof. One thing is for sure, if there's something for guests to tamper with, they will tamper with it ?

Hi all, i am looking for a small MVHR system for our holiday rental property. We have a lot of condensation and mould problems in the en-suite bathroom and the bedroom suffers slightly from the same. I am looking for a system that will cover the bedroom and en-suite and possibly the living area too (thought there’s no damp/mould etc in there). Unfortunately there’s no way I can incorporate the kitchen in the design, there’s just no way to get a duct to it. The bathroom is small (about 7sq. m) and has mostly solid stone rendered walls. The bedroom is about 22 sq. m and has one stone wall. The living area is 28 sq.m. There is a small cold loft space above the bedroom which is likely where the unit will live, thought f the unit were sufficiently small it could live in the airing cupboard off the bathroom. I had thought that I might use a Vent Axia HR100-R unit and leave the living room out of the system but with an efficiency of up to 70% in a building that struggles to maintain a comfortable temperature already I decided against it. Then I started looking at Boulder and Blauberg’s smaller units but they seem to be inefficient to run. So that brought me to Brookvent’s Aircycle 1.2 (which I have used before in a new build that we did a few years ago and was pretty happy with) but I just can’t shake the feeling that I’m using a sledgehammer to crack a nut. Does anyone have any suggestions or recommendations please. I am trying to keep the spend down (but I don’t want to cut corners) and space is at a premium so the unit needs to be reasonably compact. Thanks, Paul

? Just had a head-scratch moment. When I rechecked I couldn't make the numbers stack up. Realised I was using 70mm as the radius in my calculations rather than 35mm! ?

Fantastic explanation, many thanks indeed Jeremy!

I suppose that the losses associated with the heat exchanger alone should amount to a 10%ish loss in energy (plus ducting losses etc especially as most of the system is located in the cold roof space) but it feels like the heating system is kicking in less often than it used to. Of course that's not scientific, it could just be that we're having milder weather at the moment. I don't think that the MVHR is good at evening temps by extracting the warm air and redistributing it's energy through the vents, I rather suspect that air is being pushed and pulled through areas of the house that had no significant airflow before. Again, not scientific, more just a 'feel'.

Interesting, I haven't come across these before. I presume they use some sort of differentiator to compare two inputs?? A static and a dynamic??

Thanks for that. Makes sense that the cheap AFMs aren't really ideal for accurate measurements of such systems. As my house is quite leaky at the moment I suppose I'm aiming more for proportionally distributing the air flow based upon the room size rather than trying to achieve a particular volume per hour. That said, if I could get somewhere close that would be great. I've just looked at the spec sheet for the UT363S and it quotes a resolution of 0.01 in the range 0-99 (although it maxes out at 30m/s) with an accuracy of +-(5%+0.5m/s) which could put the readings out by as much as 30% so on a typical reading of 2m/s (which at 70mm aperture gives around 110m3 p/h) I could be getting anywhere between about 80 and 140m3 p/h. TBH that's probably close enough for my set up. As long as I'm somewhere around 100m3 p/h rather than 1000m3 p/h I'm a happy chap ?.

I too am keen to see if there's any difference in the heating fuel consumption. It'll be difficult to gauge as we haven't quite had a full year in the house yet but my initial impression is that we may consume less energy due to the temperatures in the house being "evened out". As we still have a fairly primative single thermostat arrangement we had hot and cold spots throughout the house (dispite use of TRVs and balancing radiator flows carefully etc). Now the house maintains a much more even temperature, again another unexpected benefit. We also feel the benefit of the wood-burning stove in other parts of the house as the air is moved around the building so hopefully that will contribute to any savings in fuel oil.

Hi again folks, I have had my system up and running for a few weeks now and I'm hugely impressed with the results. I initially configured the system by [semi-educated] guesswork and now that I have an anemometer to test the air flow rates it seems that I actually did far better than I could have hoped for with just a 6% difference between the total extract and total vent (in favour of the vents and therefor giving me the slight positive pressure I was looking for). ? However, I now want to balance each room more accurately so I constructed an anemometer to help. I built my anemometer using a piece of 125mm pipe with a cap on one end. I cut a hole in the cap and used hot-melt glue to attach a Uni-T UT363-S to it. I added some gasket material to the other end to make a good seal as I press it against the ceiling valves. The whole thing cost around £28 and it appears to work well. My question is this; when I do the calculation between air flow (in m/s) to volume should I use the 125mm diameter of the pipe or the 70mm of the anemometer's aperture? Common sense tells me that I should be using 70mm but a confirmation by someone more knowledgable would be great. Happy New Year to all!

I haven't been on here for a few weeks so I am late to this party. I have my system up and running now. Against a lot of good advice I went ahead with my installation in a fairly leaky, 1830's stone-built cottage. For me the primary goal was to reduce the moisure level within the house while I get around to addressing the root causes over the coming years. I am staggered by the difference the system has made to our home. We now have zero condensation on the windows in the morning (vs. having to use the Karcher Window Vacuum 4 or 5 times per window every morning!), a much drier, healthier air quality, reduced condensation on walls after showering etc and an unexpected bonus that fresh food in the pantry now lasts longer than it used to. As I get around to making the house more airtight I hope that the benefits will prove to be even more profound. For me MVHR has been an enormous game changer and I wouldn't be without it.

This is a retrofit to an 1850s stone-built house which currently leaks like a sieve. However, I am working to remedy that as far as is practicable. My primary reason for installing the MVHR (at least in the short to medium term) is to keep air moving through the house. The house has some damp areas and I am working my way around troubleshooting but it’ll be an ongoing process. In the meantime I want to try and make the house a bit drier and hopefully a bit healthier to live in. I’m prepared for the fact that the heat recovery aspect may not be hugely effective as long as the system moves air around the place and extracts damp air from bathrooms etc. Going forward I intend to install new windows and doors, dry-line some of the walls (when they are dried out etc) and go nuts with insulation. I envisage 2 to 3 years to complete the works.

Hi Again, I am am now we’ll under with my MVHR project. Something that I have been giving a lot of thought to is about how to position vents in the rooms. However, what I haven’t seen is any mention of how to position them with regard to central heating radiators. Is it wise to position vents directly above a radiator so that the convection current mixes with the incoming fresh air and warms it? Or, is it better to position it on the opposite side of the room? In a couple of my rooms that would mean siting the vent close to the doorway which I don’t want to do (unless there’s a good argument for doing so).

The loft is insulated with lovely fibreglass. The problem is that all the trusses run perpendicular to the runs of ducting. I had considered adding more insulation over the top of the existing which would allow me to run ducting in an insulation sandwich I suppose. Also, I can’t remember where I read it but I got the impression that it was no longer an acceptable practice to insulate the ducting this way?? Anyone else seen/heard that?

Thanks for all the great information. What I had in mind is very similar to what @AdamSee suggested. Probably knock up a CLS frame, screw/glue PIR on to all faces and keep one face easily removable for maintenance. I want to mount the manifolds in there too as the ones I have are uninsulated so I am guessing it will be around 1.2 x 1.2 x 0.9 or so. The unit will be mounted very close to the loft hatch so to clean filters etc I shouldn’t even need to get into the loft, I can do it from the ladder. I also plan to extend the wires to the control panel so that I can locate it somewhere more convenient in the house eliminating the need to access the unit to tweak the settings. @scottishjohn , the MVHR is indeed just a part of the solution, I have much work to do elsewhere in the building. It’ll be a long process but I am hoping that for a relatively small outlay the ventilation system will start to help and make the house more liveable. We’re also running the heating more than we normally would to help with drying the walls etc. and looking at problem areas to see how we can address the problems. I suspect a big part of the problem may be the painted cement render which covers most of the building and probably locks in a lot of the moisture in the walls, that’s a job for next year. One aspect I haven’t yet looked into is insulating the ducting - thanks for the reminder @JSHarris. It seems that the various types of insulation I have looked at appear to have only one thing in common, they are all very expensive! Is there a consensus on which type is best in terms of price/performance? I am using 75mm semi-rigid ducting.

Hi all, I installed a system based around a Brookvent unit in a new build that I did around 3 years ago and I was never entirely happy with the system. It worked well enough but I see now how I could have improved upon the system. With that little bit of knowledge and experience (and the copious amount of knowledge that I have gained reading posts on this site) I am now set to install a new MVHR system in our current property. We now live in a modest 1850s stone built, 3 bed detached house which gets little direct sunlight in the colder months. It has a 1970s extension with cavity walls (rendered concrete and thermalite block construction) which accounts for about a third of the building. Damp is a big problem and I am working through various solutions to try to help minimise the moisture entering the house such as ensuring that all guttering is performing well, surface water runs away from the house, paving levels are low enough etc. etc. Clearly I have my work cut out to make this a comfortable, healthy home for my family. There is a lot of moisture and a bit of mould is starting to develop as we come into the colder months and the windows are open less. So, part of my grand plan is the MVHR system. I have purchased the kit (based around a Titon unit) and having agonised over the design for months I am almost ready to get started. I had originally planned to locate the unit in the cold loft but it seems that current advice is to locate it, and the manifolds, in a heated part of the house. I started to look at the airing cupboard as an alternative but my wife was not entirely pleased with that solution as we have precious little storage space in the house anyway. My proposed solution (and what I would be interested to hear people’s opinions on) is to locate the unit and manifolds in the loft and construct an insulated housing around it. I also plan to put a small, thermostatically controlled heater (perhaps 25w or so) to keep the temperature up around 18-20 dec C. My questions are; is this a logical, sensible solution? Do the MVHR units need to “breathe” - does it need to be in an open environment to prevent over heating the unit? Would a heater be required or would the heat generated by the fan motors be enough to heat that small space? Any advice is greatly appreciated.