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Retrofitting ventilation system in a renovated house - airtightness
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23-02-2016 5:37pm#1Hi. I've got a 1400 sqft 4-bed, 2 storey, semi-D that I'm about to extensively renovate and build a small kitchen extension onto.
Because of a radon issue, the renovation will involve tearing up the floors and installing radon remediation measures (sump and barrier). As we're doing this, we will also be insulating the floors carefully and installing underfloor heating.
We will also be replacing all of the windows and external doors with reasonably high spec replacements, insulating the house with 100mm external wall insulation and replacing an open fire with an insert stove. Our boiler is a 2 year old condensing oil boiler. It will drive both the existing rads and the underfloor heating.
The house is currently very, very drafty (just as well, considering the radon issue). The windows and doors are badly fitted. Ventilation is a combination of holes in external walls, extractor fans in the bathrooms and an extractor hood over the hob.
We haven't given a lot of thought to ventilation in our plans to date, which was a mistake. As planned, we will still be relying on the fans and holes already mentioned. A neighbour who has just finished a similar renovation installed an MVHR system, with flexible ducting running to all the rooms in the house and a filtration and heat recovery unit in the attic. He very kindly showed me around his system and made a very persuasive case for the benefits of MVHR. I'm now interested in MVHR for our house, primarily for air quality (the heat-recovery is a nice side effect).
Some googling on MVHR systems in Ireland leads to a lot of heated discussions on the advantages/disadvantages vs demand controlled ventilation or just vents in the external walls and regularly opening windows. A lot of the discussions are from 5-6 years ago, and they're generally related to new builds rather than retrofits.
Most of the discussions reference air-tightness as a pre-req for MVHR to be effective and efficient. So I'm wondering the following:
1. If we do the work as specified above, can we expect that the house will be sufficiently airtight (assuming we tell the installers that air-tightness is an objective) for MVHR to be a realistic option. Or do we need to take other measures to ensure air-tightness?
2. Assuming that the house will be sufficiently airtight, given that we will be pulling down ceilings, tearing up floors and insulating walls anyway: does this make retrofitting MVHR to an old house a more reasonable prospect?
3. Assuming 1 and 2 above: is there anything in particular I should be discussing with our engineer in the way of particular units and ducting types? Our neighbour went for flexible plastic ducting, and I came across a reference somewhere that this can be difficult to maintain (presumably difficult to clean).
- hgTagged:1
Comments
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1. No. Yes
2. Yes
3. design for <1ach, limit thermal bridges, build to passive principles and design calcs if possible (don't install ufh if you don't manage good thermal bridge free floor details), have 20% contingency. Be realistic about your budget ( this size retrofit + extension could take you to €200k..)0 -
1. No, probably not even close. There is no guarantee that any of your planned improvements will have any positive impact on your air tightness (regardless of what the product installers tell you). Why? you do not know now where your air leakage issues are. Have a heat loss survey, which includes an air tightness test done and then make your decisions.
1. If we do the work as specified above, can we expect that the house will be sufficiently airtight (assuming we tell the installers that air-tightness is an objective) for MVHR to be a realistic option. Or do we need to take other measures to ensure air-tightness?
2. Assuming that the house will be sufficiently airtight, given that we will be pulling down ceilings, tearing up floors and insulating walls anyway: does this make retrofitting MVHR to an old house a more reasonable prospect?
3. Assuming 1 and 2 above: is there anything in particular I should be discussing with our engineer in the way of particular units and ducting types? Our neighbour went for flexible plastic ducting, and I came across a reference somewhere that this can be difficult to maintain (presumably difficult to clean).
Besides, you wont get any meaningful answer on the internet without a hell of a lot more information about your house.
2. Yes
3. The first thing I would want to know from my engineer is what experience has he/she with similar projects. If little or none, then I would be looking for
for someone who does. There are several aspects to mvhr which should be understood before deciding on system/ductwork/routing etc. I've seen so many poorly installed due to total lack of understanding of the subject.0 -
Thanks for the feedback.
I had thought about doing an air-tightness test before kicking off, but it didn't seem to be tremendously useful prior to doing major structural work and extensively revising the structure of the building. Any results would surely be invalidated by knocking the back wall, tearing up the floors, and replacing all the doors and windows?
Since the house was going to get wrapped in EWI, I guess I figured that it would be impermeable (assuming it was competently installed). And since the windows and doors were getting replaced, I'd similarly figured that they wouldn't be installed in such a way as to permit air leakage. As for thermal bridging through walls etc. I had assumed that EWI would mitigate that. To ensure that our new extension wouldn't represent a opportunity for bridging, we're insulating that also with EWI (so there's no seam between it and the house).
I may have been a bit optimistic. And I take the point that it's impossible for someone on the internet to speculate without essentially having plans and site survey. But can I ask though, other than doors, windows, walls and floors, where else could a house be suffering air leakage? I'm assuming that internal air leakage isn't a problem (could I be wrong about this?). So that kinda just leaves the ceilings/roof, right?
As for UFH, again, I'd figured that tearing up the floors and taking the time to insulate them properly might be sufficient. I hadn't considered that the floors could form a thermal bridge to the outside. Again, I was thinking the EWI would cover me where they connect to the external walls, and the installation of insulation beneath (75mm screed, 150 mm aeroboard).
The thing that really shook me is the figure of 200K. Again, this is something that's being described on the internet, and I mightn't have communicated my plans particularly well. But that's way, way in excess of anything we would have expected. For example: the EWI and windows/doors alone have been quoted at approx 25K (supply and fit). The extension is a 20 sqm box with a leanto roof. We haven't gotten a figure for the entire job yet, but our ballpark budget is so much lower than 200K. I was thinking a decent ventilation system might add 10K to the build, at worst - and that since we were doing all of the other work (floors up, ceilings down), I might regret not going the last mile and installing a modern system.
I take the point about ensuring that engineer knows what he's at. I'll raise some of this with him and see where we go from there. Thanks again for the input.0 -
Thanks for the feedback.
I had thought about doing an air-tightness test before kicking off, but it didn't seem to be tremendously useful prior to doing major structural work and extensively revising the structure of the building. Any results would surely be invalidated by knocking the back wall, tearing up the floors, and replacing all the doors and windows?
Since the house was going to get wrapped in EWI, I guess I figured that it would be impermeable (assuming it was competently installed). And since the windows and doors were getting replaced, I'd similarly figured that they wouldn't be installed in such a way as to permit air leakage. As for thermal bridging through walls etc. I had assumed that EWI would mitigate that. To ensure that our new extension wouldn't represent a opportunity for bridging, we're insulating that also with EWI (so there's no seam between it and the house).
I may have been a bit optimistic. And I take the point that it's impossible for someone on the internet to speculate without essentially having plans and site survey. But can I ask though, other than doors, windows, walls and floors, where else could a house be suffering air leakage? I'm assuming that internal air leakage isn't a problem (could I be wrong about this?). So that kinda just leaves the ceilings/roof, right?
As for UFH, again, I'd figured that tearing up the floors and taking the time to insulate them properly might be sufficient. I hadn't considered that the floors could form a thermal bridge to the outside. Again, I was thinking the EWI would cover me where they connect to the external walls, and the installation of insulation beneath (75mm screed, 150 mm aeroboard).
The thing that really shook me is the figure of 200K. Again, this is something that's being described on the internet, and I mightn't have communicated my plans particularly well. But that's way, way in excess of anything we would have expected. For example: the EWI and windows/doors alone have been quoted at approx 25K (supply and fit). The extension is a 20 sqm box with a leanto roof. We haven't gotten a figure for the entire job yet, but our ballpark budget is so much lower than 200K. I was thinking a decent ventilation system might add 10K to the build, at worst - and that since we were doing all of the other work (floors up, ceilings down), I might regret not going the last mile and installing a modern system.
I take the point about ensuring that engineer knows what he's at. I'll raise some of this with him and see where we go from there. Thanks again for the input.
25k for Windows & Ewi : don't bother with Mvhr0 -
Demand Controlled Ventilation might be suitable for you - it's "optimium" air tightness requirements are less than MHRV and is fairly cheap (say €3k by the time you're finished, maybe less - depends on ducting routes for the extract)0
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Hi. I've got a 1400 sqft 4-bed, 2 storey, semi-D that I'm about to extensively renovate and build a small kitchen extension onto.
Because of a radon issue, the renovation will involve tearing up the floors and installing radon remediation measures (sump and barrier). As we're doing this, we will also be insulating the floors carefully and installing underfloor heating.
We will also be replacing all of the windows and external doors with reasonably high spec replacements, insulating the house with 100mm external wall insulation and replacing an open fire with an insert stove. Our boiler is a 2 year old condensing oil boiler. It will drive both the existing rads and the underfloor heating.
The house is currently very, very drafty (just as well, considering the radon issue). The windows and doors are badly fitted. Ventilation is a combination of holes in external walls, extractor fans in the bathrooms and an extractor hood over the hob.
We haven't given a lot of thought to ventilation in our plans to date, which was a mistake. As planned, we will still be relying on the fans and holes already mentioned. A neighbour who has just finished a similar renovation installed an MVHR system, with flexible ducting running to all the rooms in the house and a filtration and heat recovery unit in the attic. He very kindly showed me around his system and made a very persuasive case for the benefits of MVHR. I'm now interested in MVHR for our house, primarily for air quality (the heat-recovery is a nice side effect).
Some googling on MVHR systems in Ireland leads to a lot of heated discussions on the advantages/disadvantages vs demand controlled ventilation or just vents in the external walls and regularly opening windows. A lot of the discussions are from 5-6 years ago, and they're generally related to new builds rather than retrofits.
Most of the discussions reference air-tightness as a pre-req for MVHR to be effective and efficient. So I'm wondering the following:
1. If we do the work as specified above, can we expect that the house will be sufficiently airtight (assuming we tell the installers that air-tightness is an objective) for MVHR to be a realistic option. Or do we need to take other measures to ensure air-tightness?
2. Assuming that the house will be sufficiently airtight, given that we will be pulling down ceilings, tearing up floors and insulating walls anyway: does this make retrofitting MVHR to an old house a more reasonable prospect?
3. Assuming 1 and 2 above: is there anything in particular I should be discussing with our engineer in the way of particular units and ducting types? Our neighbour went for flexible plastic ducting, and I came across a reference somewhere that this can be difficult to maintain (presumably difficult to clean).
- hg
You really need to reconsider underfloor heating with a boiler and rads upstairs, search on here there are plenty of treads on the subject0 -
25k for Windows & Ewi : don't bother with Mvhr
On the basis that they're unlikely to be airtight after installation? You might be right.
Having done a little bit more reading, it looks like airtight/draught-free is a much higher standard than I had thought, and even more difficult to reach in a retro-fit.
Thanks.0 -
You really need to reconsider underfloor heating with a boiler and rads upstairs, search on here there are plenty of treads on the subject
You're not the first person to express skepticism about this. It's already been pointed out that this system will be less efficient than running the ufh from a heat pump, and it will require some complex plumbing. As I understand it, the plumbing would involve a recirculating water from the rads and/or using a buffer tank. The verdict I got was "it's possible, but expensive to install and still less efficient than simply using rads".
I had a look through some other threads. And the story is similar: if the plumber knows what they're at, it can be done. But that doesn't mean it's a necessarily a good idea.
I still like the idea of UFH (for comfort), and I'd be willing to sacrifice /some/ efficiency for it. But it's beginning to sound like a non-starter.
thanks.0 -
I had thought about doing an air-tightness test before kicking off, but it didn't seem to be tremendously useful prior to doing major structural work and extensively revising the structure of the building. Any results would surely be invalidated by knocking the back wall, tearing up the floors, and replacing all the doors and windows?
You are not looking for a result, but rather the leakage areas, paths and mechanisms.0 -
1. Since the house was going to get wrapped in EWI, I guess I figured that it would be impermeable (assuming it was competently installed).
2. And since the windows and doors were getting replaced, I'd similarly figured that they wouldn't be installed in such a way as to permit air leakage.
3. As for thermal bridging through walls etc. I had assumed that EWI would mitigate that. To ensure that our new extension wouldn't represent a opportunity for bridging, we're insulating that also with EWI (so there's no seam between it and the house).
1. You don't repair a puncture on a bicycle wheel by patching the tyre and similarly wrapping with ewi will do nothing for air tightness on a house
2. Unless specifically specified in conjunction with the wall makeup, they will leak.
3. What about the other junctions, such as wall to roof and at window / door reveals. For instance, are you moving the windows forward so that the frames are wrapped in the ewi?0 -
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I may have been a bit optimistic. And I take the point that it's impossible for someone on the internet to speculate without essentially having plans and site survey. But can I ask though, other than doors, windows, walls and floors, where else could a house be suffering air leakage? I'm assuming that internal air leakage isn't a problem (could I be wrong about this?). So that kinda just leaves the ceilings/roof, right?
Wrong. I regularly see floor coverings on 1st floors being lifted up by 2 to 3 inches when house is under test for air tightness. Therefore, free flowing external air going through the void between downstairs ceiling and upstairs floor, i.e. through the centre of the house.0 -
PartlyOn the basis that they're unlikely to be airtight after installation? You might be right.
Having done a little bit more reading, it looks like airtight/draught-free is a much higher standard than I had thought, and even more difficult to reach in a retro-fit.
Thanks.
But you need to be realistic about the cost of retrofitting a 1400ftsq house and 20msq ext0 -
See this in a magazine before and thought it might help you
http://passivehouseplus.ie/magazine/upgrade/ireland-s-first-fully-passive-retrofit.html0 -
See this in a magazine before and thought it might help you
Thanks. That house is very, very similar to mine - down to the radon concerns. Interesting to see how crucial air-tightness was and how difficult it was to achieve. I don't think anything like that is achievable on our budget and timescale. But very interesting read.Partly
But you need to be realistic about the cost of retrofitting a 1400ftsq house and 20msq ext
You might be right. 200K would be prohibitive though. Most of our works are downstairs (approx 800 sqft) and we're not going for particularly expensive finishes. As against that, it's an old house so who knows what might turn up during the build. We're still awaiting a quote for the building works.MicktheMan wrote: »1. You don't repair a puncture on a bicycle wheel by patching the tyre and similarly wrapping with ewi will do nothing for air tightness on a house
2. Unless specifically specified in conjunction with the wall makeup, they will leak.
3. What about the other junctions, such as wall to roof and at window / door reveals. For instance, are you moving the windows forward so that the frames are wrapped in the ewi?
Having done a bit more reading on air-tightness, all of this makes more sense now. I have no idea whether the window frames will be wrapped in the EWI, I suspect not. I'll talk to our engineer.
We won't be able to achieve passive house standard, and it seems we almost certainly won't be tight enough for MVHR. It might be more "best effort" than "best standard". But something is better than nothing. I'll do some reading on demand-controlled ventilation...
Thanks all.0 -
We renovated a 2400sqft Victorian end of Terrace. Large Solar gain as all bar one of the DG windows are South and West facing. The walls are two foot thick. The attic and ground-floor was insulated and 5 of the 6 bedrooms external walls had insulated plasterboard fitted because there was no existing cornice work to interfere with. All other rooms just replastered. 3 open Fireplaces. French doors cumulatively open about an hour a day Winter or Summer for a Claustrophobic trio of dogs
Our gas bill for the year is about €1900.
That article linked says that the Passive House cost component of the renovation was €84,000 ex Vat. So the cost to the owner for the Passive materials and fitting was €100,000?? Their heating bill is now €55 a year. Thats great.
If we had have done the likes of that, we'd save just over €1800 a year in heating bills!!
Sure...it'd only take till the year 2071 for us to break even!! :rolleyes:
What am I missing? 0 -
Comfort factor. The house is never too hot (0r rarely, maybe in the depth of summer?) and never too cold. Temperature just sits!0
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I was forgetting about the mortgage interest on that extra €100,000 spend. The article says all 'do anyway' costs were removed to arrive at the €84,000 ex Vat. Even if new DG/TG windows were left in the Passive costs which might balance out the mortgage interest, one still can't get around the €100,000 figure in the end.
In my case, not having to wait 30 minutes for my rads to warm the house up to temp for 4 months of the year or 5 with a bad winter is not worth a payback period of 55 years.
I Dunno, maybe Passive specs make sense in Scandinavia, Russia, Canada, Minesota etc with 6 months of minus 20c but here in Ireland?0 -
Calibos,
I live in an old house too and it's hard to keep at a nice temp. I reckon I spend about the same as you on heating.
However, when I retire I expect to be spending a lot more time in the house as I won't be at work where the heating is paid for by my employer. So my heating bills will probably go up significantly.0 -
Updating this thread. I ignored the advice offered here, and went ahead with a HRV system. The house is externally insulated, triple glazed windows, etc. etc. We just moved back in, so I'll keep this updated to serve as evidence of my idiocy/acuity, depending on how it all goes.
As far as airtightness went, my ultimate instruction to the builder was "make a sensible effort, but no heroic measures". Which is to say: airtightness was a concern (so use proper membranes and tape, and don't put stupid holes in things) but not something to obsess over (no wasting time testing and sealing and retesting to achieve some notion of perfection). So, more "air-resistant" than "air-tight". This was driven as much by lack of pre-planning, budget and time as by any grand theory. I noted the article posted earlier in the thread where they spent an awful lot of time apparently just chasing a number and I decided it just wasn't for me.
I took the advice of my engineer, builder and some ventilation and insulation specialists as to whether a HRV ventilation system would make sense in the context of the build I was planning. The answer was pretty uniformly: "it'll be fine. not as efficient as it theoretically might be, but fine". Of course, someone who's trying to sell you a ventilation system would be inclined to tell you this anyway.
I sent the house plans to a few different companies to get quotes for HRV, which all came in between 3K and 4.5K. I did consider demand controlled ventilation, but never found a solution that I liked or that was as simple as HRV. I ultimately went with a company that quoted me 3.5K (incl. VAT) for supply and fit of a system with ducting and vents. The system is a Ventaxia Sentinel Kinetic Plus B, and we ultimately placed it in the attic.
Due to the tightness of some of the spaces we went for flexible ducting over the installers preferred option of rigid ducting. Because we had the walls and ceilings torn up anyway, installing the ducts involved minimal disruption. There was only one location where we had to box in some ducting running down a wall. We have extract from 5 locations, supply to 6.
First fix took a day. Second fix and commissioning took about 2.5 hours.
The system was turned on for the first time yesterday. The fan is set up to run @ 40% during the day (low hum detectable upstairs if the house is completely quiet) and @ 25% during the night (basically inaudible). However, because the moisture sensor is detecting a lot of moisture in the house, it's actually been boosting away @ between 65% and 85% for the last 24 hours. Noise-wise, that's bassy white-noise hum, not dissimilar to the sound of an oil boiler a couple of rooms away. Noticeable, but not impossible to sleep through.
The installer has explained this as the system detecting and drying out the fresh plaster/paint/concrete and it should settle down after a couple of days. The system does actually have a "building dryout mode" which is designed to run full boost in an unoccupied new dwelling for a week or so before occupying. If I was to do it all over again, I might have chosen to get the second fix done prior to actually moving back in and engaging this mode (although it would have encountered a lot of dust, necessitating an early filter change I reckon).
And that's it. I'll update with how we get on in case anyone comes looking for first-hand information down the line. I'm happy enough with what I've seen so far, bearing in mind that my priority was comfort and ease-of-use over efficiency. I might put together a separate post on how the renovation went over all if anyone is interested. Back when I was in the planning/research stage of our job, I was very interested in "after-action-report" style posts from people who (like myself) were completely clueless about construction.
-hg0 -
Three other notes, addressing questions raised earlier in the thread:
1. The windows were set out and wrapped in the EWI. This had the nice side-effect of giving us really deep window boards inside.
2. We decided against under floor heating due to the complexity of the plumbing involved in mixing it with rads. This saved us a lot of time, money and hassle.
3. We sprayed the rafters and gable wall in the attic with 6 inches of breathable foam insulation, making the attic a warm (and hopefully reasonably airtight) space. This cost about 2K. I haven't figured out what to do with the old fibreglass insulation that's still up there other than bundling it up and moving it off to the sides.0 -
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Great thread hengilas.
How much did you spend in the end on the entire retrofit and extension?
Do you know what the BER is now compared to when you started?0 -
I think in a renovation its really your call of course you wont get all the benefits of MHVR as with a passive house but that does not mean its still not worth doing
I live in a 1960s Semi Got it externally insulated and installed a MHVR also Vent axia and i know its not as efficent as it could be but after a number of years of use I would never be without it
Air quality in House is so much better and no hole in the wall vents no condensation no mould etc0 -
Updating this thread. I ignored the advice offered here, and went ahead with a HRV system. The house is externally insulated, triple glazed windows, etc. etc. We just moved back in, so I'll keep this updated to serve as evidence of my idiocy/acuity, depending on how it all goes.
As far as airtightness went, my ultimate instruction to the builder was "make a sensible effort, but no heroic measures". Which is to say: airtightness was a concern (so use proper membranes and tape, and don't put stupid holes in things) but not something to obsess over (no wasting time testing and sealing and retesting to achieve some notion of perfection). So, more "air-resistant" than "air-tight". This was driven as much by lack of pre-planning, budget and time as by any grand theory. I noted the article posted earlier in the thread where they spent an awful lot of time apparently just chasing a number and I decided it just wasn't for me.
I took the advice of my engineer, builder and some ventilation and insulation specialists as to whether a HRV ventilation system would make sense in the context of the build I was planning. The answer was pretty uniformly: "it'll be fine. not as efficient as it theoretically might be, but fine". Of course, someone who's trying to sell you a ventilation system would be inclined to tell you this anyway.
I sent the house plans to a few different companies to get quotes for HRV, which all came in between 3K and 4.5K. I did consider demand controlled ventilation, but never found a solution that I liked or that was as simple as HRV. I ultimately went with a company that quoted me 3.5K (incl. VAT) for supply and fit of a system with ducting and vents. The system is a Ventaxia Sentinel Kinetic Plus B, and we ultimately placed it in the attic.
Due to the tightness of some of the spaces we went for flexible ducting over the installers preferred option of rigid ducting. Because we had the walls and ceilings torn up anyway, installing the ducts involved minimal disruption. There was only one location where we had to box in some ducting running down a wall. We have extract from 5 locations, supply to 6.
First fix took a day. Second fix and commissioning took about 2.5 hours.
The system was turned on for the first time yesterday. The fan is set up to run @ 40% during the day (low hum detectable upstairs if the house is completely quiet) and @ 25% during the night (basically inaudible). However, because the moisture sensor is detecting a lot of moisture in the house, it's actually been boosting away @ between 65% and 85% for the last 24 hours. Noise-wise, that's bassy white-noise hum, not dissimilar to the sound of an oil boiler a couple of rooms away. Noticeable, but not impossible to sleep through.
The installer has explained this as the system detecting and drying out the fresh plaster/paint/concrete and it should settle down after a couple of days. The system does actually have a "building dryout mode" which is designed to run full boost in an unoccupied new dwelling for a week or so before occupying. If I was to do it all over again, I might have chosen to get the second fix done prior to actually moving back in and engaging this mode (although it would have encountered a lot of dust, necessitating an early filter change I reckon).
And that's it. I'll update with how we get on in case anyone comes looking for first-hand information down the line. I'm happy enough with what I've seen so far, bearing in mind that my priority was comfort and ease-of-use over efficiency. I might put together a separate post on how the renovation went over all if anyone is interested. Back when I was in the planning/research stage of our job, I was very interested in "after-action-report" style posts from people who (like myself) were completely clueless about construction.
-hg
Great post. Thx. How is system working for you now? Happy with noise levels, running costs?0 -
I have a much longer update in draft somewhere. But, long story short: I'm happy out with the ventilation and insulation systems. No issues with noise, the running cost of the system itself is negligible (haven't got a good measure of its impact on the heating costs for the house in isolation). We could have made more of an effort with the air-tightness in one or two areas, but really no complaints.0
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I have a much longer update in draft somewhere. But, long story short: I'm happy out with the ventilation and insulation systems. No issues with noise, the running cost of the system itself is negligible (haven't got a good measure of its impact on the heating costs for the house in isolation). We could have made more of an effort with the air-tightness in one or two areas, but really no complaints.
Hi Hengilas.
Just out of curiosity where would you have made more of an effort? Doing a similar project & want to get the best advice & tips along the way.0 -
Hi Hengilas.
Just out of curiosity where would you have made more of an effort? Doing a similar project & want to get the best advice & tips along the way.
Hard to be certain without doing an air-blower test. However...
Once we moved back in and were marvelling at the overall lack of draughts and how warm the place was, on cold days we noticed a draught coming from underneath the door of our main bathroom.
We'd previously renovated that bathroom, so it didn't get gutted in the bigger renovation. The instruction to the builder was to leave that bathroom alone as much as possible. Putting a hand up to the wooden surround of the bath, there was a noticeable cold airflow coming through the gaps. And so we surmised that behind that surround, where there were penetrations of the wall for drains, taps, pipes, etc. there wasn't any air tightness measures.
Now, the entire house is wrapped in insulation, so you could legitimately ask how outside air is able to get in, given that the insulation is reasonably airtight itself. The answer is that there is an internal wall in the house that was previously an external wall (so it has a cavity). That wall extends all the way up to the roof, and presumably it has access to external air somewhere up there (beyond the insulation). The penetrations for pipes and whatnot are likely allowing air from that cavity in under the bath. And the HRV in the bathroom (which is set to suck, rather than blow, cos it's a wet-room) is sucking that unfiltered, unheated air into the bathroom, and because it's colder than the ambient air in the house, it's draughting out under the bathroom door and down the stairs (it's an top-of-the-stairs bathroom).
It's not a huge draught, and only noticeable when it's freezing outside. But it is an air leak, and it means that some of the air going into the heat exchanger of our HRV is actually unheated, reducing its theoretical efficiency somewhat. It's an annoyance, and one we'll hopefully resolve soon when we replace the ancient bath that's there. But I'd reiterate that we were never expecting 100% air-tightness, and if we weren't planning on replacing the bath anyway, I wouldn't be too bothered about it.
In larger terms, the other thing I'd point up re: air-tightness is kitchens and cookery. I can't remember if it's been mentioned elsewhere in this thread, but being airtight means that you're not going to be venting your cooker hood to the outside (because that's a leak). So instead, you'll wind up with a recirculating hood. Which is useless. It sucks the air from the hob through a carbon filter (which just takes the edge off the smell) and sends it straight back into the kitchen. If you're frying mackerel, the smell won't leave your kitchen for a while. But here's the thing, you will also likely have a suck vent in your kitchen connected to the HRV. So (at least in my kitchen) the mackerel air goes through the carbon filter which removes some (but not all) of the mackerel-ness from the air. Then that air floats around in the kitchen until it gets sucked into the vent, its heat recovered in the HRV, and vented straight out into the open air.
Given that the HRV already has a suck vent in the kitchen, why not connect it straight to the hood? Well, firstly, you'll want to filter the mackerel air before sending it to the HRV (to remove grease and other gunk). Secondly, you want the kitchen to be ventilated even when the hood isn't sucking. Thirdly, the entire HRV system runs at one speed for the entire house (or at least, mine does, cos it's centralised). Meaning: if any part of the house boosts the system to go for a "super-extract" (for example, if we have a shower), then every vent in the house will boost. So, having a shower in one bathroom will lead its vent to suck more, which will lead a bedroom vent to blow more. So, when you turn on your HRV-connected kitchen hood, you're purging air from the entire house, not just the kitchen.
There are HRV systems that have fancy cooker vent solutions, but ours is a lot simpler. There is one big fan, and many vents. Some suck, some blow. If the HRV detects that their air coming into it is polluted in some way (moisture mainly), it will automatically increase its speed until it can no longer sense the pollution. In practice this means it boosts for about 3 to 4 minutes after a shower. It never boosts because of cookery, likely because the kitchen is part of a large open plan airspace, and the pollution is too dispersed to trigger the sensor. If we do fry mackerel, and the smell is bothering us, we push the "purge" button on the HRV control and it clears the air pretty quickly (I guess, if we were clever, we'd connect the recirculating fan to the purge button somehow, so when the cooker fan is switched on it automatically boosts the entire system while its on...which is probably what the fancy solutions do, come to think of it).
Long story short: if you go the airtight HRV route, your kitchen may not clear air as quickly as it would in a leaky house. If your kitchen is isolated from your living areas air-wise (ie: behind a door), that probably won't matter. If it's open plan, you still have options. One tip I picked up from another boards thread, don't be tempted to light scented candles to mask the smell in the kitchen, HRV systems don't like them (not sure why, wax condensing in the ducts maybe?).
I should add, nothing about a HRV forbids you from opening a window if you need to. It will just temporarily reduce the efficiency of the heat exchange. That said, we rarely open any windows, and there are windows in my house that I haven't opened since I moved back in (18 months ago). It's just never been necessary.0 -
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Henglias your full of information I never thought of when it comes to this craic.
I'm renovating a 20 year old house. Pumping the walls, dry lining the inside & installing a heat pump.
I'm unsure about heat recovery or Demand control ventilation which one would my house be more suited to. Like you I want to stop as much unnecessary drafts as possible but I know I won't get it airtight so is there much point in installing a MHVR system that won't be running to its full capability???0 -
Henglias your full of information I never thought of when it comes to this craic.
I'm renovating a 20 year old house. Pumping the walls, dry lining the inside & installing a heat pump.
I'm unsure about heat recovery or Demand control ventilation which one would my house be more suited to. Like you I want to stop as much unnecessary drafts as possible but I know I won't get it airtight so is there much point in installing a MHVR system that won't be running to its full capability???
I had an awesome blow by blow account of my entire renovation and all of its costs and problems written somewhere as a draft, and it's lost to the void. So I'm not going to go into mad detail, but here's some stuff I know...
1. I knew nothing about construction before I began. And having completed the job, all I know about construction pertains to my build specifically. I'm a complete amateur. That was actually a bit of an advantage, because I knew what I didn't know, if that makes any sense. Our house had previously been renovated/butchered by a complete moron, who - because he knew how to mix concrete - thought he could do it all himself. Amongst the many horrors he left in his wake was a doorway he'd cut into a load-bearing wall without bothering to put in a proper lintel, so the door-frame was a structural element.
2. Following on from that, I'm hopelessly unqualified to give advice to anyone else. Even looking back over this thread...I got two pieces of advice. Don't do HRV, and don't do underfloor heating. I'm glad I didn't listen to the first piece of advice (offered in good faith, and with no plans etc. to go on) and I'm glad I did listen to the second (UFH would have been way too complicated to plumb and manage).
3. Get professional advice. If you think your build is straightforward, you're probably wrong. We had an engineer and a very competent builder and it wasn't enough, there were knowledge/judgement gaps all over the place.
From my experience as a rank amateur, "building science", the interplay of ventilation, insulation and heating...treating your house a single complex system which has interlocking sub-systems which feedback into each other...is vital no matter what you're doing. And the construction professionals I encountered had very variable skills in this area. You might get a guy who is a great structural engineer, but is basically chancing his arm when it comes to the science stuff. Or a builder who reckons he knows "all that stuff", and thinks it's just a matter of slapping on insulation and calling it a day (not my builder, I hasten to add, who was happy to admit when he didn't know something). If you're making radical changes to the insulation/ventilation/heating of your house, then its vital to get advice from someone who can treat it as a single project and give recommendations that will ensure the changes you make synergise with each other. You come across horror stories of condensation streaming down the walls of newly insulated houses because they'd gotten the ventilation wrong.
I spent ages googling and reading papers published in various journals, trying to get a handle on "best practice" in the area, trying to figure out if 10 years from now there'll be news stories about the rash of idiots who put external wall insulation on their house in the 2010s and now their houses are uninhabitable because it fell off/caught fire/evaporated/ate the house. You can find a series of stories in the British press from a few years back about cavity wall insulation that has had horrific problems with damp (a specific product I think). I found a bunch of literature about experiments that had been run in Germany (I think), where they'd built houses decades ago with the specific purpose of monitoring how they aged and what happened when you try different renovation techniques on them. They were monitoring for condensation etc. etc. What I got from reading all this stuff was that a) I didn't really understand it beyond the basics and that b) an awful lot of the people I encountered in the industry didn't seem to understand it either...but they didn't necessarily know that.
3a. If you do get advice (especially on the internet) make sure it's appropriate to your project. I came across an awful lot of stuff about passive new builds which was interesting, but in many ways irrelevant. The things that are possible in a new build, being built to passive standards with no sunk cost in existing systems/structures aren't always possible in a renovation. I came across a few people who were "chasing a number" around airtightness and passiveness and had lost sight of common-sense/value-for-money. Maybe that makes sense if your motivation is eco-friendliness or you just really like knowing that your house has the "best" number. Anyway, the point is a lot of the advice I saw on the internet was of the "well, I wouldn't start from there" type. Which isn't tremendously helpful. You want to know what it is you want to achieve: comfort? efficiency? eco-friendliness? whatever you can for a given budget?
4. It'll cost more than you think. I know a bunch of people who've recently completed builds/renovations. Without exception, they all went over-budget. Not a single exception. Now, maybe the people I know are unusually bad at planning, but I think it's just a fact of life. It costs more than you think. Luckily for me, my job didn't cost as much as the 200K figure mentioned earlier in this thread, but we were north of 100K when we moved back in, and still needed to do some landscaping and a few other odds and ends. For reference, our original budget was 50K (like, when we bought the house we thought it would take 50K to do it up). Once we got quoted for the straightforward stuff like insulation and windows, and realised how much work we'd need to do (floors, ceilings, etc) we revised up to 80K. In fairness to the builder, he never misled us, and never felt like we had a hope of bringing it in under 100K. About two months into the build, we revised to 100K. By the time we'd finished, and including things like moving fees, rent while were out of the house and random stuff like skip hire, we were a decent way towards 120K. It will cost more than you think. We were lucky that we hadn't originally planned to stretch to the fullest extent of our ability to pay, but it was a close run thing for a finish. Attempting to do underfloor heating, for example, would have killed us off.
5. I don't know anything about dry-lining or heat pumps. We avoided dry-lining even though it was (significantly) cheaper because it made some of the internal planning more complicated, and we needed to re-render the outside of the house anyway, so the EWI was more attractive. We'd recently bought a new oil boiler, so weren't interested in getting a heatpump. We did pump one internal cavity wall, sort of experimentally (against the advice of the builder) and I don't think it made much difference. Since it was an internal wall, I'm not even sure what the thinking was. I do remember the builder pointing out that in our well-insulated house, we had an internal cavity wall that would act as a giant heat sink, absorbing the warmth in the house, using it to warm up the air in its cavity, and then radiating/convecting away straight up out the top of the house. At the point in the build where we realised that, there wasn't a huge amount we could do about it, so I got that one wall pumped as a sort of "hail mary" pass (thinking maybe that the internal heat wouldn't penetrate into the wall or something). It cost about 200 quid and we got a bit of a discount because we had the same people in spraying attic insulation at the same time. I don't know if it made any difference, but I suspect it did very little. The wall is a bit cooler to the touch than others in the house.
5a. One thing you didn't mention in your list is heating controls. We have an oil boiler with 3 zones (upstairs, downstairs, big watertank) and 3 thermostats. Having an easy-to-use digital controller for the heating/hot-water has probably had as much of an impact on our oil bills as many other significantly more expensive things. Again though, this stuff all works in concert. I can set the downstairs thermostat to 18 degrees, hear the boiler bump on for a few minutes, and feel the house warm up almost instantly (no heat loss from air, no heat loss from walls/windows). And once the house gets warm it more or less stays that way, the boiler can shut down for long periods, blipping on for a minute or two every so often to maintain the heat. It's not quite the "you can heat the entire house with a single candle" level that Passive builds can get to. But the house is always comfortable and takes a lot less oil than it did previously.
5b. Also not mentioned: attic insulation. It's often low-hanging fruit in any cold house, and is cheaper than many other things that you can do.
6. Is your house airtight enough for HRV? I haven't a clue. Mine is, I think, just about. But then, I replaced all my windows and doors, tore up all my floors and ceilings, replastered loads of stuff, and wrapped the entire house in styrofoam. Not all of that was directed at airtightness, but I imagine it had an effect, cumulatively. If your house is draughty now, and all you do is pump the walls and dry-line, I don't think that's going to make a huge difference. But then, what do I know?
7. Get impartial professional advice before making big changes to the thermal underpinnings of your house. It'll cost more than you think. That's about it, I'd say.0 -
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