Starting to think about MVHR

[MikeGrahamT21]

MVHR has always been high on my 'want' list for a number of reasons, and I plan on installing myself, with the help of a design (found several companies who will design free of charge, has anyone had any dealings with anyone they're recommend?).

 

For the MVHR unit, I really like the look of the Brookvent Aircycle 1.2, its SAP Q listed, 93% efficient, and has all the sensors and bypasses we'd want out of a unit, anyone used one before?

 

We do have a number of pro's and con's with it all though:

 

On the plus side...

• Our extract rooms are all south facing, and gather considerable heat without doing anything additional i.e. cooking, showering, and our supply rooms are joined on to another house, and generally remain cooler (great in summer, not so much in winter). At present when we cook, we open the windows to let out the steam and smell, wasting all that heat, and in the bathroom we have a single extractor fan which pulls out an incredible amount of heat, you don't realise until you feel it from the outside. So one of the major pluses for me would be the balance and distribute that heat throughout the house.
• Live in a bungalow where the loft isn't to be built in, so plenty of room for the unit and all the pipework (Considering the 75mm radial ducting, with manifolds, to keep pipework as simple as possible).

 

On the negative side...

• We have a neighbour with a wood burner, and in winter it puthers smoke, and absolutely stinks, this is a major concern, as we don't want that smoke in the house, is there a way round this? I suppose good enough filters should get rid?
• The house certainly isn't airtight at present, and this is something I am doing the best I can, room by room, but it is taking time. Obviously using Jeremy's spreadsheet, I can see ventilation loses soon mount up with poor airtightness, however I was thinking if there was a way to ensure that the extract and the supply was balanced (perhaps having the same number of both types), would this really make any difference to how we are now? I appreciate if one was slightly out, you'd either push warm air out, or import cold air. Or is simply because the supply and extract are in different rooms, and instead of drawing air under the door into the other room, it would come from the gaps? I'm not sure how achievable low ACH is in our house, but already the doors are starting to get harder to close which I'm guessing is a good sign? We are a 1968 build bungalow, so the walls are wet plastered (thank god), i'm ripping up all the floors anyway as the joists have woodworm, and putting a breather membrane (taped) down before the floorboards (OSB3 smart ply), and I'm ensuring all the windows are well sealed. Recently had a practice run in our new utility, and with everything closed bar one door, if you try and slam the door it bounces back off the air, but again i'm not sure what level of ACH that would equate to, and don't want to pay to have it measured. I did think about making my own blower door, just to find air leaks more than anything with a smoke pen?

 

Another question is can we use a roof tile vent for one of the in/out sources? Currently we already have a 100mm hole in the loft wall to the outside which was from an old extractor fan, which I'd like to use, and rather than drilling another, use a roof tile vent instead? Would that work if it snows?

 

Any input would be greatly received.

[ragg987]

MVHR in a "leaky" house seems pointless, so as you have pointed out this needs to be taken care of. It might be worth getting a pressure test to judge how you are doing and before you invest a few thousand pounds and many hours of your time on this - older buildings will likely have air leaks all over the place incuding under skirts and cills. Passiv standard is 0.6 ACH or below at 50Pa, older houses are going to be in double or even triple figures. So your heat recovery with MVHR is going to be small unless this is sorted.

 

MVHR will not distribute heat in the house (easy trap to fall into). The extracted air (say 21C) will warm incoming air in the heat exchanger  - e.g. incoming air will raise to 16C if close to freezing outside. Air at 16C is still too cold to heat your house. And even if 16C was warmer than the room it is going into, the delta temperature is too low to actually heat the room unless your airflow is massive.

 

Have you considered local extractors with heat exchangers e.g. in the bathrooms and kitchen? random google search https://www.vent-axia.com/range/lo-carbon-tempra-selv

 

For a supplier, I used BPC based on other recommendations here and on eBuild. Might be worth taking their input.

 

 

[Jeremy Harris]

Designing the duct runs and terminal positions is pretty easy, especially with a radial ducting system, so there's no real need to employ someone to do it, IMHO. 

 

MVHR won't do much about moving heat in or out of any room, as the flow rate is far to low to be of any real use.  Similarly, unless the house is pretty airtight (a lot better than required by building regs) then MVHR may well not work very well.  I doubt a 1968 built bungalow is anywhere near airtight enough, there are likely to be large leaks around all the wall to ceiling joints, leaks that look invisible until you do a blower test and then hear them all whistling away.  Our old 1980's built bungalow was just like this, wet plastered block walls, decent uPVC Dg windows and doors, lots of time spent by me going around sealing up every leak I could find and I doubt I got the airtightness below about 20 ACH...................

 

Smoke is a problem with  MVHR.  We had a neighbour that used to have bonfires, and the MVHR would quickly suck smoke in and circulate it through the whole house.  The filters don't remove smoke at all (we have the finest input filter, a pollen filter).  All you can do when there is smoke around outside is turn the MVHR off until such time as the smoke has cleared, unfortunately.

 

You can run MVHR intake and exhaust pipes up through the roof OK.

 

[Dudda]

You need to do an airtight test before you go any further. Really you'd want to be looking at 3 ACH or lower for a MVHR system to work right.

What I'd suggest first is doing a temporary one yourself with a household fan taped in an open window. Someone did it on this forum and has photos etc. Go around with a smoke pen or similar and seal as much as you can. You're not going to be able to work out an accurate ACH reading or find all the small gaps but you should be able to find the main ones and improve it a good bit. Then I'd get a proper pressurised airtight test done and again go around and seal as much as you can. You should hopefully be looking for smaller leaks at this stage.
My biggest worry is the ceiling in your bungalow. You'll have lots of air escaping through all the ceiling lights particularly if you've a lot of recessed spots. You'll also have air escape through electrical sockets and light switches which are difficult to rectify.

If after the airtight test you're still up around 7 or 8 ACH with tape and airtight mastic everywhere I think it's time to say you gave it you're best but going any further is a waste of time and money. The house will be slightly better as you've reduced the air leakage. However if you're now down in the 3-4 ACH (which will be very hard to achieve) you can consider progressing and looking further at units and duct runs.

[MikeGrahamT21]

Very glad I asked about this now.

 

Wasn't aware of the fact that MVHR won't shift the heat, that is a real shame! So sounds like air testing is the best thing to do, whether we go for it or not.

 

We do have spot lights, I plan on installing the airtight boxes behind them next year when I bump up the loft insulation. I also plan on sorting the sockets and switches out as best as I can, but will definitely need some kind of fan to do this properly, i'll see if I can concoct something using the left over plywood i've got.

 

Yeah I looked into the single room MVHR for the bathroom, but because I was considering the whole house unit, I didn't go any further with it, maybe this would be more worth while.

 

At what point would the house become 'unhealthy' if I try and airtight, but don't get it to an MVHR level?

 

So the smoke is going to be a major issue, i had a bad feeling about that! And in winter they have it on every day, multiple times, so basically the MVHR would be off most of the time, which would be rather pointless, they've just taken delivery of another pallet of the damned stuff!!

 

One final thought was a university paper i read from the university of leeds, from years ago (early 2000's), they did some basic airtightness in a number of council properties (going no better than 10ACH from about 28ACH), in half installed demand controlled, and in the other half MVHR. Now this was of interest to me, and the results showed in the MVHR ones, a massive reduction in CO2 (very important to me as I work at home, as well as live here), and not a massive increase in energy requirements, which is what made me think that the airtightness wouldn't be a total killer! Mind saying that, if smoke is an issue, then its a no go anyway! For any type of MVHR! :-( Annoying that we like is a smokeless zone too...

[Dudda]

54 minutes ago, MikeGrahamT21 said:

At what point would the house become 'unhealthy' if I try and airtight, but don't get it to an MVHR level?

Varies due to occupancy, size and volume of house, what extractor fans you have and how much they're on, how often front doors or windows are opened etc but in the region of below 3-5 ACH you'd want to start considering mechanical ventilation or additional wall or window vents.

[MikeGrahamT21]

OK, and I'd be right in thinking that 3-5ACH is going to be quite hard to achieve? How hard would it be to close a door at those levels as an example?

[ragg987]

Closing a door seems completely arbitrary as a way to measure air tightness. Will depend on speed of closure, gap below door, pressure being applied, volume of air in the room, door size, plus of course what is happening on the other side (outside the room).

 

All this can tell you is relative to before you sealed it.

 

Having never done an air test on an older property, I can only guess, and I would say getting that low on a 1960s bungalow is not going to be easy.

 

Remember, the test is at 50Pa pressure (to simulate a windy day, I believe), which while low as an absolute number is surprisingly high in the context of a building.

[jack]

1 hour ago, MikeGrahamT21 said:

OK, and I'd be right in thinking that 3-5ACH is going to be quite hard to achieve? How hard would it be to close a door at those levels as an example?

 

We're below 0.6 ACH and closing doors is fine.

 

Interestingly, no matter how windy it is, if only one external door is open the wind will never slam it shut! 

[oranjeboom]

Interesting thread as I'm retro-extending a 1950's bungalow build, but have the advantage that it's all been gutted (windows, slab, plumbing and most ceilings). So most escape routes I hope to cover with careful detailing. I think the biggest routes of escape in a renovation job is around windows inserted in cavity walls where bits of plastic will cover up a multitude of sins. Taking out my old uPVC windows certainly showed lots of air routes past the frames or through the bodge cavity filled foam from the 1980s.

 

When it comes to ceilings and cold loft spaces, I have thought about:

•  laying an airtight membrane over the ceiling plasterboard and joists,  taping up joins as needed and along the perimeters (wall plates, gable walls) taping up around the joist/wall junction silicone around the area where the joist fits into the wall (or use this stuff: http://www.ecomerchant.co.uk/liquid-blowerproof-brush-paint-on-airtight-sealing-membrane-5kg.html)
• using air-tight downlighter hoods where required
• silcone any electrical conduits that serve switches, and sockets in the rooms below
• silicone any plumbing that punctures the ceilings
• cover with loft insulation
• using beading on the roomside wall/ceiling junction (https://www.screwfix.com/p/no-nonsense-plasterers-corner-bead-tape-50mm-x-30m/45720)

 

It's not going to catch all air paths from the rooms downstairs but will help to some extent. My only concern is maybe static caused by the membrane/polysheet covering all the electrical cabling and also trapping moist air from below in the joists etc. Perhaps they latter should not become an area for trapped moisture! So maybe stick polythene sheet under the existing pb ceiling and then add a new pb layer (pb/sheet/ old pb).

 

 

 

[MikeSharp01]

55 minutes ago, oranjeboom said:

out:

•  laying an airtight membrane over the ceiling plasterboard and joists,  taping up joins as needed and along the perimeters (wall plates, gable walls) taping up around the joist/wall junction silicone around the area where the joist fits into the wall (or use this stuff: http://www.ecomerchant.co.uk/liquid-blowerproof-brush-paint-on-airtight-sealing-membrane-5kg.html)

Plaster is, as I understand it, a good air tight layer.

[MikeSharp01]

3 hours ago, jack said:

Interestingly, no matter how windy it is, if only one external door is open the wind will never slam it shut!

Yes I have rusty hinges on my barn doors no wind will blow them shut.

[MikeGrahamT21]

Yeah, the closing door thing is obviously not a very good way of testing, but without machinery I thought it wasn't too bad to see how i'm getting on, coincidentally, the doors are definitely harder to shut the more work i do, as said with the utility you physically cannot slam the door closed, no matter how hard you try.

 

I had a think last night, how much air would a load of 100mm delta fans (computer fans) fixed onto plywood push? I remember they are quite powerful (and noisy!). How much air does a blower fan push? (I'm guessing quite a bit). I certainly would like to depressurise the house to get a better understanding of where all the leaks are, some are obvious i.e. the big hole in the kitchen floor under the oven, but I know there will be a lot of smaller less obvious ones.

 

Since the idea of MVHR is now just a fading memory courtesy of our neighbour, i won't be going to extremes in order to avoid poor air quality, but i will still be laying taped membranes under the floors in order to do the best that I can, which has always been the goal, taking the principles of what is done to achieve passive house standards, and applying them as best as I can to our house without spending silly amounts of money, I think this will go a good way to reducing our energy demands, and indeed year on year we are requiring less gas for example (I know its hard to directly compare one year to another as they are so different).

[Jeremy Harris]

I don't think the door closing thing is relevant, really.  Our new house has a tested air permeability of well below the Passivhaus 0.6 ACH level, yet I can slam any of the internal doors if I wish, with no obvious restriction. 

 

I'm more inclined to think that pressure causing a door to be reluctant to slam may well be as a result of directional air leakage.  When I made up and fitted my home made blower rig to our old house, it tended to make internal doors slam on its own, or make some doors difficult to close, when it was running.  This was just because it was pressurising or depressurising some rooms from leakage and it doesn't take much to get a door to be hard to close, I found.

[Crofter]

I assumed that the OP must be referring to slamming exterior doors, as these are the ones with a tight seal.

Internal doors have a decent gap at the bottom after all.

[jack]

4 hours ago, MikeGrahamT21 said:

Yeah, the closing door thing is obviously not a very good way of testing, but without machinery I thought it wasn't too bad to see how i'm getting on, coincidentally, the doors are definitely harder to shut the more work i do, as said with the utility you physically cannot slam the door closed, no matter how hard you try.

 

What sorts of gaps do you have around the doors (and underneath in particular)?

[MikeGrahamT21]

1 hour ago, Crofter said:

I assumed that the OP must be referring to slamming exterior doors, as these are the ones with a tight seal.

Internal doors have a decent gap at the bottom after all.

Yeah I was referring to the external doors, sorry!

 

The internal doors are also a tiny bit harder to close, these have a 10mm gap underneath, and when you open them with force with no windows open, you often hear the ceiling making a few clicks, with the air rushing in through any small gaps (and i know there are some!)

[MikeGrahamT21]

4 hours ago, JSHarris said:

I don't think the door closing thing is relevant, really.  Our new house has a tested air permeability of well below the Passivhaus 0.6 ACH level, yet I can slam any of the internal doors if I wish, with no obvious restriction. 

 

I'm more inclined to think that pressure causing a door to be reluctant to slam may well be as a result of directional air leakage.  When I made up and fitted my home made blower rig to our old house, it tended to make internal doors slam on its own, or make some doors difficult to close, when it was running.  This was just because it was pressurising or depressurising some rooms from leakage and it doesn't take much to get a door to be hard to close, I found.

With a level of 0.6ACH, is the slamming only possible because you have the MVHR vents in place? As this would balance the pressure difference between the rooms, which I presume is what makes the action slightly harder, i.e. it has to balance via the door opening whilst its getting smaller.

[Alex C]

Being able to slam a door in an airtight house is just down to how big the gap is under your door. My bedroom doors have about 7-8mm and you can slam them but my downstairs wc which is a massive 2.4 high door only has about 3mm from door to tiles and you cant slam that bugger however hard you try. I need to get round to taking a couple more mm off the bottom to help with air circulation. I should have make the kids bedroom doors a tighter fit so they couldnt slam them.

[MikeGrahamT21]

Back to my home made blower...

I've found the specs of another blower door online, which states:

Maximum flow @ 50 Pa

5450 cfm (9265 m3/h)

Highest flow of any portable blower door

 

Our house is only small, so I'm not going to need anywhere near that surely?

 

I've had a thought about using 1 (or maybe 2 to get near this value) car radiator fans?

http://www.ebay.co.uk/itm/16-120w-Aeroline-High-Power-Electric-Car-Engine-Radiator-Cooling-Fan-/172428823084?epid=0&hash=item28258f0a2c:g:YKQAAOSwkNZUq~Yv

This one will push 2500CFM for £30...

 

What do you think? Linked up to some kind of potentiometer to vary the speed?

[Crofter]

It was a car radiator fan that Damian Hart Davies used on his DIY blower kit, he documented it in a blog somewhere- anyone have a link?

[Jeremy Harris]

Car radiator fans work very well, and are massively over-powered for the job, even in a very leaky house.  This is the set up I built some years ago now:

 

 

 

This fits tightly into one of the windows in our old house, and has a speed control knob that allows the fan speed to be adjusted.  In practice the fan only needs to turn slowly, if it's run at full speed there is a howling gale blowing through the house.

 

The old radiator fan I bought from the local scrapyard had a rusted out motor, which was a nuisance, so I had to replace it with a brushless model aircraft motor I happened to have.  This then allowed the model aircraft motor electronic speed control to be used, connected to a servo tester that has the knob wired to it.

 

If you can get hold of a working 12V car radiator fan, then you can use a cheap speed controller from Ebay,  plus a 12V car battery or decent mains power supply (radiator fans draw around 10 to 20 A, so need a decent supply) to do pretty much as I did.

 

I found that the bigger leaks, like all the wall to ceiling junctions, howled like a banshee when the house was de-pressurised, so were easy to find!

[gravelld]

On 25/09/2017 at 14:24, MikeGrahamT21 said:

OK, and I'd be right in thinking that 3-5ACH is going to be quite hard to achieve? How hard would it be to close a door at those levels as an example?

 

I think this really depends on what the extent of the work is. Someone here: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15252&page=1 got 1ACH on their work and two others are mentioned. If you're going fully tea cosy (roof and walls) I think you can go a long, long way. I am aiming for 3ACH on my own project.

Edited September 26, 2017 by gravelld

[MikeGrahamT21]

20 hours ago, JSHarris said:

Car radiator fans work very well, and are massively over-powered for the job, even in a very leaky house.  This is the set up I built some years ago now:

 

 

 

This fits tightly into one of the windows in our old house, and has a speed control knob that allows the fan speed to be adjusted.  In practice the fan only needs to turn slowly, if it's run at full speed there is a howling gale blowing through the house.

 

The old radiator fan I bought from the local scrapyard had a rusted out motor, which was a nuisance, so I had to replace it with a brushless model aircraft motor I happened to have.  This then allowed the model aircraft motor electronic speed control to be used, connected to a servo tester that has the knob wired to it.

 

If you can get hold of a working 12V car radiator fan, then you can use a cheap speed controller from Ebay,  plus a 12V car battery or decent mains power supply (radiator fans draw around 10 to 20 A, so need a decent supply) to do pretty much as I did.

 

I found that the bigger leaks, like all the wall to ceiling junctions, howled like a banshee when the house was de-pressurised, so were easy to find!

Thanks! As soon as I saw the car radiator fan I thought it would be ideal, and very cheap too!

 

Do you have a link to a speed controller? I'll have to give this build a go at some point, should help me massively moving forwards. Got some plywood coming up for use, its temporary flooring at the moment, so this will be a good use of it :-)

[MikeGrahamT21]

I contacted BPC for a free quote, they didn't seem too concerned about the smoke issue, said that the units all come with filters which should get rid of it, and if its too bad, they sell an £800 carbon filter as an extra which would see it off. Opinions on this? I know someone recommended BPC, but they seem to be saying the exact opposite of you guys, and its a lot of money to spend!