Anyone got an MVHR?
Discussion
arun1uk said:
Do you know what else needs servicing? The fan unit and motor itself?
As I understand it (and I should stress that I'm a designer/specifier of the things as part of the architectural design process, not an installer) the main thing apart from filters and cleaning of the registers (outlets) is the 'balance' of the registers. These are adjustable, so that the amount of flow from each can be controlled. The idea is that you 'balance' the amount of resistance they offer in each room, so that the amount of circulation is equal throughout the house. Obviously, without such balancing, the rooms nearest the fan unit would get all the flow, and hardly any circulation would reach the rooms furthest from the fan.
The system is balanced on installation, but due to the convoluted routing of the ducts and the fact that the ducts accumulate a certain amount of dust, grime and fluff, particularly on bends, they can go out of balance over time. It's therefore a good idea to get them re-balanced every few years (I'd suggest maybe every 5 years).
Knowing how much filth builds up in (larger) air conditioning ducts, I have reservations about the long-term maintenance of the domestic MVHR systems we're fitting these days - I can imagine the ducting getting so badly clogged that it stops working altogether - but that's another question, I guess.
Some interesting points, I'm surprised at how many people I have met in the building trade who don't understand MVHR and the number who have never even heard of it. I am slowly learning as our build progresses and a point worth mentioning is that you can't have extraction in your kitchen and bathrooms, it will just fight the system, recirculation is the only option.
I’d also recommend removing the heat exchanger and giving it a rinse out every year or so - despite the filters it does get clagged up over time.
As already said, the biggest bonus is in winter - condensation is a problem for well sealed modern houses, the air changing makes a huge difference. Made a big difference to our house, which isn’t exactly airtight, so in theory the system is a waste of time here!
If I’m following correctly the water thing shouldn’t need filling up - it collects moisture in the base of the unit then sends it to drain (tapped into soil pipe etc) via a U bend that prevents drain smells getting back in - I’m wondering whether yours is missing the bend in the drain pipe?
As already said, the biggest bonus is in winter - condensation is a problem for well sealed modern houses, the air changing makes a huge difference. Made a big difference to our house, which isn’t exactly airtight, so in theory the system is a waste of time here!
If I’m following correctly the water thing shouldn’t need filling up - it collects moisture in the base of the unit then sends it to drain (tapped into soil pipe etc) via a U bend that prevents drain smells getting back in - I’m wondering whether yours is missing the bend in the drain pipe?
Blue62 said:
Some interesting points, I'm surprised at how many people I have met in the building trade who don't understand MVHR and the number who have never even heard of it. I am slowly learning as our build progresses and a point worth mentioning is that you can't have extraction in your kitchen and bathrooms, it will just fight the system, recirculation is the only option.
A bathroom has a higher level of water vapour than other rooms but I don't think that would be a problem for the MVHR unit. Kitchens may have higher grease levels but couldn't that be caught by a grease filter on the extract grille?herewego said:
Blue62 said:
Some interesting points, I'm surprised at how many people I have met in the building trade who don't understand MVHR and the number who have never even heard of it. I am slowly learning as our build progresses and a point worth mentioning is that you can't have extraction in your kitchen and bathrooms, it will just fight the system, recirculation is the only option.
A bathroom has a higher level of water vapour than other rooms but I don't think that would be a problem for the MVHR unit. Kitchens may have higher grease levels but couldn't that be caught by a grease filter on the extract grille?But it's wise to use that recirculating cooker hood as much as possible, and to change its filters regularly, as otherwise all the grease and smoke particles coming off your cooking will be happily coating the MVHR extract duct from the kitchen, exacerbating the problems I mentioned above.
I have to say that I'm a bit out-of-step with current fashion, in that I'm fairly heavily set against highly airtight dwellings that then rely on MVHR: I think we're obsessing too much about energy efficiency, at the cost of a healthy living environment. But who am I to blow against the wind?
Equus said:
I think that Blue6's point is that you can't have separate extraction (ie. an extractor canopy over your cooker hood) - you've got to use a recirculating cooker hood.
But it's wise to use that recirculating cooker hood as much as possible, and to change its filters regularly, as otherwise all the grease and smoke particles coming off your cooking will be happily coating the MVHR extract duct from the kitchen, exacerbating the problems I mentioned above.
I have to say that I'm a bit out-of-step with current fashion, in that I'm fairly heavily set against highly airtight dwellings that then rely on MVHR: I think we're obsessing too much about energy efficiency, at the cost of a healthy living environment. But who am I to blow against the wind?
I don't disagree, but these days if you're building from scratch it is a given. We expressly didn't want passiv but due to building regs have ended up with a house that will be fairly airtight (below 3) and therefore need MVHR. On the up side I will have a dry toothbrush every morning and expect to feel the benefit of breaking in fresh air in the house, but it's going to be about 10 months before I can report back!But it's wise to use that recirculating cooker hood as much as possible, and to change its filters regularly, as otherwise all the grease and smoke particles coming off your cooking will be happily coating the MVHR extract duct from the kitchen, exacerbating the problems I mentioned above.
I have to say that I'm a bit out-of-step with current fashion, in that I'm fairly heavily set against highly airtight dwellings that then rely on MVHR: I think we're obsessing too much about energy efficiency, at the cost of a healthy living environment. But who am I to blow against the wind?
Blue62 said:
I don't disagree, but these days if you're building from scratch it is a given.
Not really.I would say you need MVHR with a design figure below about 3.5, but you certainly don't need that level of airtightness to comply with current building Regulations.
I'm willing to bet that in 20-30 years time, we'll look upon the deliberate design of very high levels of airtighness and the current (very crude and simplistic) managed ventilation systems we're fitting at the moment as design defects similar to those on the system build housing of the 1950's and '60's:
"Of course it was a dumb thing to do, but they didn't fully understand the implications of what they were doing. We know better, now!"
My personal view is that you're better off designing only to moderate levels of airtightness, and accepting some energy overhead as a necessary part of maintaining a healthy internal environment.
I’ve often been intrigued by these, our house having the bulk of its living space on one floor with roof space above it’s something I could realistically fit myself fairly easily.
The thought of fresh air and even temperature appeals greatly and although not recent it’s new enough and hi spec enough to benefit I suspect.
Are there suppliers who cater to the diy installer?
The thought of fresh air and even temperature appeals greatly and although not recent it’s new enough and hi spec enough to benefit I suspect.
Are there suppliers who cater to the diy installer?
The problem in 20-30 years time will be people living in sealed boxes switching the things off, not maintaining them etc. Then they'll be living in mushroom farms.
Re the kitchen question, in theory you shouldn't have an extractor in conjunction with MVHR, but in practice it seems to be ok, although that may be because our house isn't that airtight. The MVHR just doesn't run strong enough to act as an over-cooker extractor, it just ticks over gently, even on boost the power isn't anywhere near the most basic kitchen extractor hood.
Bathrooms have a boost pullswitch that can dispatch most of the condensation as it's created, clearing the rest gradually, unless it's well below freezing outside, then we can have a touch of condensation beading up at the base of the window glass for the rest of the night.
2 stoves here too, which could theoretically kill you to death if you have an MVHR system running.
DIY - loads of suppliers out there. I fitted ours, I used spiral wound galv steel ducting with steel fittings that have rubber lip seals, just cut to length and push together. It's mouseproof unlike the flexi plastic ducting, if that's a concern. Been running nearly a decade now, well worth doing for comfort and allergy prevention, regardless of any energy savings.
Re the kitchen question, in theory you shouldn't have an extractor in conjunction with MVHR, but in practice it seems to be ok, although that may be because our house isn't that airtight. The MVHR just doesn't run strong enough to act as an over-cooker extractor, it just ticks over gently, even on boost the power isn't anywhere near the most basic kitchen extractor hood.
Bathrooms have a boost pullswitch that can dispatch most of the condensation as it's created, clearing the rest gradually, unless it's well below freezing outside, then we can have a touch of condensation beading up at the base of the window glass for the rest of the night.
2 stoves here too, which could theoretically kill you to death if you have an MVHR system running.
DIY - loads of suppliers out there. I fitted ours, I used spiral wound galv steel ducting with steel fittings that have rubber lip seals, just cut to length and push together. It's mouseproof unlike the flexi plastic ducting, if that's a concern. Been running nearly a decade now, well worth doing for comfort and allergy prevention, regardless of any energy savings.
andy43 said:
The problem in 20-30 years time will be people living in sealed boxes switching the things off, not maintaining them etc. Then they'll be living in mushroom farms.
I think there's a problem beyond that, and it exists right now.MVHR systems only have a small number (usually just one) register per room, which means they don't mix and distribute fresh air as effectively as natural infiltration.
There is also a limit to the number of air changes per hour you can achieve, simply because drawing large volumes of air through single registers and small diameter ducts generates noise, and that becomes intolerable to occupiers.
Taken together, it means that the air isn't as 'fresh' as it could be, and harmful pathogens build up - not always visibly or noticeably. Welcome to Sick Building Syndrome.
A colleague who lives in Sweden told me MHRV is falling out of favour there - he said you can never completely eliminate the background noise and it's yet another of those things that people are increasingly becoming intolerant of. He said there's also concern about running the fans all the time as everything else gets lower energy.
Blimey, the future's bleak! I was banking on the fact that a properly installed and balanced system will provide healthy fresh air and welcome relief for my hay fever suffering wife.
I do take the points Equus makes, he seems to know his stuff and I have to say that during the design process the whole issue of airtightness was pretty much taken out of our hands by the architect, though my eventual intervention meant that we did not go as far as passiv. We have got plenty of opening windows and ceiling vents and the whole unit will be in a 'control room' which will be sited in the garage, it will be interesting to see how it all pans out.
I do take the points Equus makes, he seems to know his stuff and I have to say that during the design process the whole issue of airtightness was pretty much taken out of our hands by the architect, though my eventual intervention meant that we did not go as far as passiv. We have got plenty of opening windows and ceiling vents and the whole unit will be in a 'control room' which will be sited in the garage, it will be interesting to see how it all pans out.
I've lived in an air tight timber frame house for 9 years with one. Never had a problem, no condensation, little noise unless it's on boost (after you've had a s
t), handy in the summer as it has the summer bypass function so blows in cool air at night. It took the wife some getting used to as she loves opening windows, even in the middle of winter!
t), handy in the summer as it has the summer bypass function so blows in cool air at night. It took the wife some getting used to as she loves opening windows, even in the middle of winter!Equus said:
Not really.
I would say you need MVHR with a design figure below about 3.5, but you certainly don't need that level of airtightness to comply with current building Regulations.
I'm willing to bet that in 20-30 years time, we'll look upon the deliberate design of very high levels of airtighness and the current (very crude and simplistic) managed ventilation systems we're fitting at the moment as design defects similar to those on the system build housing of the 1950's and '60's:
"Of course it was a dumb thing to do, but they didn't fully understand the implications of what they were doing. We know better, now!"
My personal view is that you're better off designing only to moderate levels of airtightness, and accepting some energy overhead as a necessary part of maintaining a healthy internal environment.
Hmmm, going against percieved thinking there with your last statement. But i agree!I would say you need MVHR with a design figure below about 3.5, but you certainly don't need that level of airtightness to comply with current building Regulations.
I'm willing to bet that in 20-30 years time, we'll look upon the deliberate design of very high levels of airtighness and the current (very crude and simplistic) managed ventilation systems we're fitting at the moment as design defects similar to those on the system build housing of the 1950's and '60's:
"Of course it was a dumb thing to do, but they didn't fully understand the implications of what they were doing. We know better, now!"
My personal view is that you're better off designing only to moderate levels of airtightness, and accepting some energy overhead as a necessary part of maintaining a healthy internal environment.
You are probably right to how it will be viewed in future. There is not a chance that anything other than a very small percentage of these systems will be working properly 10 years from now. On the upside, the standard of genreal house building in this country is so poor, moderate levels of air tightness is likely all that will be achieved!
monkfish1 said:
Hmmm, going against percieved thinking there with your last statement. But i agree!
You are probably right to how it will be viewed in future. There is not a chance that anything other than a very small percentage of these systems will be working properly 10 years from now. On the upside, the standard of genreal house building in this country is so poor, moderate levels of air tightness is likely all that will be achieved!
I am certainly sceptical, but for all the research i have done, articles read and users spoken to, I can't find any substance whatsoever for your assertion that 'there is not a chance...working in 10 years time.' You are probably right to how it will be viewed in future. There is not a chance that anything other than a very small percentage of these systems will be working properly 10 years from now. On the upside, the standard of genreal house building in this country is so poor, moderate levels of air tightness is likely all that will be achieved!
I'd be genuinely interested if you can back this up, I have a series of meetings scheduled with my M&E bloke and would like to challenge him on a number of points, the life expectancy of the system will be high on the agenda. Thanks in advance.
Blue62 said:
I am certainly sceptical, but for all the research i have done, articles read and users spoken to, I can't find any substance whatsoever for your assertion that 'there is not a chance...working in 10 years time.'
I'm not as negative as Monkfish about the long term maintenance viability, but two questions I've yet to have satisfactorily answered by the manufacturers I've spoken to:- The filters are manufacturer and model specific, and the systems are manufactured in relatively small numbers. Ask how any manufacturer intends to guarantee supply of suitable filters in decades to come, even if they as a company become insolvent.
- Having seen the amount of st that builds up in large-volume air conditioning ducts (ask any air conditioning engineer: it really is quite disgusting), even in buildings such as offices where there are no rooms generating large amounts of cooking grease or moisture, how do you prevent inaccessible, small diameter convoluted pipework gradually clogging up with muck, dust and fluff over many years?
Don't get me wrong, though: I'm not actually against MVHR, per se, as part of an energy efficiency and ventilation strategy. Just that you can get fanatics (PassivHaus) who take the principle too far - in this case by insisting on very high levels of airtightness, such that the building is entirely reliant on MVHR for air quality - frequently combined with heating systems that are incapable of coping if you have to resort to purge ventilation and misguided application of passive solar that focuses too much on winter gains, and not enough on avoiding summer overheating.
Equus said:
My personal view is that you're better off designing only to moderate levels of airtightness, and accepting some energy overhead as a necessary part of maintaining a healthy internal environment.
This is my view too. When I start my next self-build it will be open windows that give me fresh air I have yet to meet anyone with the system installed who has anything negative to say other than noise, but in the main it seems most people are oblivious to it after a while, which i guess is understandable. Thanks Equus for your points, I will take them to the next meeting and if Monkfish gets the chance to back up his statement I'd be grateful, this is supposed to be a 'forever house', so longevity is a key concern.
Dont know about "back it up". I think you misunderstand me?
It a piece of equipment. Of course it can be made to work for 10 years.
However it often wont be because (as well as for the reasons Equus states), people dont/wont/cant understand it. Therefore it will be left. neglected or whatever.
In other words, im not suggesting there is a technical issue. More of an understanding/education issue.
The OP who started this post probably counts as one of the rare few who actually bothered to ask the question what it was for and researched it.
Most homeowners simply wont know. They will open the window.
Would be interesting do do a survey of systems 5 years after installation to see the state of them and if they are even turned on!
It a piece of equipment. Of course it can be made to work for 10 years.
However it often wont be because (as well as for the reasons Equus states), people dont/wont/cant understand it. Therefore it will be left. neglected or whatever.
In other words, im not suggesting there is a technical issue. More of an understanding/education issue.
The OP who started this post probably counts as one of the rare few who actually bothered to ask the question what it was for and researched it.
Most homeowners simply wont know. They will open the window.
Would be interesting do do a survey of systems 5 years after installation to see the state of them and if they are even turned on!
Equus said:
I'm not as negative as Monkfish about the long term maintenance viability, but two questions I've yet to have satisfactorily answered by the manufacturers I've spoken to:
Agree with this too.- The filters are manufacturer and model specific, and the systems are manufactured in relatively small numbers. Ask how any manufacturer intends to guarantee supply of suitable filters in decades to come, even if they as a company become insolvent.
- Having seen the amount of st that builds up in large-volume air conditioning ducts (ask any air conditioning engineer: it really is quite disgusting), even in buildings such as offices where there are no rooms generating large amounts of cooking grease or moisture, how do you prevent inaccessible, small diameter convoluted pipework gradually clogging up with muck, dust and fluff over many years?
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