A Blower Door Can’t Tell You How Much Mechanical Ventilation You Need
With the help of people who know a lot more than I do, I’m slowly getting this stuff figured out. I wrote about my problems with using ACHnat a while back, and when I posted that article at Green Building Advisor (GBA) recently, Stuart Staniford wrote one of those comments that left me thinking, Dang, I should have known that.
Staniford, another physicist I’ve known since 2005 through my peak oil obsession, pointed out that there really is something we need ACHnat for when he wrote, “there’s no other way to turn the infiltration rate into btus, right?” D’oh! Of course, and we need to turn infiltration rate into BTUs for energy modeling, something I’m in the middle of teaching to two new crops of home energy raters over the next two weeks (here in Atlanta and then in Toronto).
The issue came back into focus for me a couple of weeks ago when I wrote about the little ventilation dustup between John Krigger and Paul Raymer, two other folks who know more than I. When I posted that article at GBA this week, I added the following bit to it after going back and reading one of my favorite Joe Lstiburek articles.
Blower doors and mechanical ventilation
One problem in the great ventilation debate is that weatherization and home performance crews are trying to using blower doors to determine if they need to add mechanical ventilation. Joe Lstiburek wrote about this issue in his article http://www.buildingscience.com/documents/insights/bsi-053-just-right-and-airtight. After opening with praise for using a blower door to help make homes more airtight and to measure leakage, he then wrote:
But then they think that a blower door actually is a precise measuring tool for how air will leak across the building during service. Wrong. Even more serious an issue is to then take the leap that using a wrong assumption about the results of an approximate measurement can be used to decide that mechanical ventilation is not needed. Bad, very bad, and potentially deadly.
I wrote about the problems with ACHnat at GBA recently, and that’s what Joe’s referring to above. What he says they do at Building Science Corporation is, “To me, the ventilate right part is easy: put in a ventilation system and pick a rate.” In footnote 4 of that article, he describes that their method is to install a system that’s capable of providing 1.5 times the ventilation rate recommended by the latest version of ASHRAE 62.2.
This is an important debate because we want homes to have less air leakage. We also want them to have good indoor air quality, and that means mechanical ventilation. Krigger makes some good points about all the resources going into training for ASHRAE 62.2, but the time has come to drop the Building Airflow Standard and stop pretending that blower doors can tell us how much mechanical ventilation a home needs.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has written a book on building science. You can follow him on Twitter at @EnergyVanguard.
Related Articles
Residential Ventilation Smackdown — The Battle Over Simplicity
It’s the Hole – Understanding What a Blower Door Is for
Just Right and Airtight by Joseph Lstiburek
Comments are closed.
This Post Has 44 Comments
Comments are closed.
Oklahoma must be really
Oklahoma must be really behind the times. I’m just not seeing ventilators installed EVER. Blower door test on new or remodeled homes? Doesn’t happen. I sometimes wonder if anybody in the state even owns a blower door or installs ventilators. None of the local supply houses stock them. Are ventilators that common in other parts of the country?
A blower door should
A blower door should absolutely be used as a “tool” in identifying whether or not fresh air is required, particularly in retrofit situations.
1.5 times Ashrae 62.2….wow. I was at a new construction house near Atlanta, GA the other day, an extremely cold one by our standards, and we set the air cycler to 100cfm continuous (Ashrae on this home was closer to 60cfm), and the already “oversized” furnace could not meet the set point of 72…you could argue that an air cycler via return plenum is not ideal for bringing in fresh air and I would not argue but w/ limited budgets, it is the option most adopted to meet the standards.
Further, I really appreciate the infiltration “credit” as discussed here, which also requires a blower door:
http://www.resnet.us/uploads/documents/conference/2012/pdfs/Raymer-Working_Through_ASHRAE62.pdf
Assume that the Bad, Very Bad and Potentially Deadly involves combustion safety testing procedures and protocols to manage or isolate the combustion appliances.
Allison-
Allison-
I was planning to comment on your GBA post but didn’t get around to it, so I guess I’ll post something here.
Many low income weatherization homes start at 20 ACH50 or higher and after air sealing and insulation work is completed are still pretty leaky — maybe at 12 ACH50 or more. Should the weatherization agency use $800 of its limited funds to install a fan in that fairly leaky house and increase their energy costs?
What sort of impact on health do you think that fan will have?
The bottom line is that the estimated infiltration credit is important to consider in ventilation and the argument has been about how mkuch credit to provide. It’s just ridiculous to suggest that every home needs a mechanical ventilation system — even if you can’t get the blower door up to 50pa. The title of this post is just plain wrong.
Also, you and Joe are both wrong about how well we can estimate natural infiltration from blower door measurements. The correlation between blower door measurements and energy usage is quite strong. If you don’t believe we can estimate infiltration from blower door tests then you should also agree that we can’t estimate solar gain from window SHGC values and you should even start to wonder if we can estimate heating loads across assemblies from R values. All of these conversions from material properties to actual building performance require estimates and simplifications. The accuracy of these estimates for infiltration isn’t a whole lot worse than many other estimates we make in modeling a home.
I’m also surprised how you (and Joe) are so adamant about mechanical ventilation but then think we can rely on occupants to set their own ventilation rates. That would be a good idea if radon, asbestos, CO, and other pollutants were all smelly — but they aren’t.
I’m glad to see this article
I’m glad to see this article point out that a blower door is not meant to determine how much mechanical ventilation is needed, but what air sealing measures are needed. Every home needs mechanical ventilation, and most need additional air sealing. But the reality is there are homes which, even with the greatest efforts, are leakier than we’d like. Adding mechanical ventilation at 1.5 times 62.2 on top of the remaining infiltration may well increase a weatherization client’s energy bill. That’s a huge disservice to those on a subsistence income.
Paul Francisco’s graph on the WAPTAC FAQs website readily points out the flaws with allowing infiltration as a means of ventilation. No stack effect and no wind translates to no ventilation. But in upstate NY, it’s rare that we have those kinds of days, and when we do, we tend to open all the windows.
Scandinavian countries ensure adequate ventilation in tight homes year round without mechanical ventilation; they open the windows once or more per day. It’s called vädra. They’ve been ensuring adequate IAQ for centuries this way.
LBL is developing a ventilation controller that takes into account delta T, humidity, occupancy, etc. It’s called RIVEC. Dialing back mechanical ventilation as it gets colder (or hotter) is a good idea in the real world where we can’t get perfectly tight homes. But will 62.2 allow for this more intelligent approach?
Unfortunately, infiltration must remain part of the ventilation equation until such time as adequate funding is provided to address ventilation the way the 62.2 committee intended.
Bob,
I
Bob,
I have been building Green Homes in the Tulsa area for three years with Energy Recovery Ventilators. These homes are tested with blower doors/ duct blasters and have HERS indexes in the low 50’s/ high 40’s. You are correct, Not many builders build Green in OK. .Regards, Larry.
Leakage as a proxy for fresh
Leakage as a proxy for fresh air? Maybe if you have no experience testing IAQ over time. But its little better than measuring my feet when sizing for gloves.
Some tight houses have great iaq, some lose houses have terrible iaq. A blower door measures tightness, not air quality.
This argument will be mute shortly. We will have devices that MEASURE air quality. Shortly following these devices will control your ventilation (is becoming more common to use expensive CO2 monitors for control now, though I’m not convinced CO2 levels are great proxy for IAQ)
In the meantime, always recommend mechanical ventilation to your clients. Get them used to the idea houses need fresh air, and cya in the event it is later discovered their air quality is a problem.
The correlation between a
The correlation between a blower door number and average infiltration over a year is pretty good if there are no large pressure induced effects by mechanical systems. As such a blower door number can be used to estimate yearly energy usage after large pressure effects are “fixed’.
There is a huge leap required to take this “average yearly infiltration” information and use it as a proxy for determining acceptable ventilation rates in houses for heath reasons. To do so requires a belief that average annual exposure is the appropriate metric for health reasons. I believe that that is incorrect and that the appropriate exposure metric should be on the order of hours not a year. If you accept this then a blower door is not the approach to take for reasons that are quite obvious since you don’t know the size of the hole, the location of the hole or the pressure difference acting across the hole. Therefore the air change rate from hour to hour or day to day does not correlate to a blower door number. Our tracer gas work and many others has shown this repeatedly.
We recommend “sizing” systems at 1.5 times the ASHRAE rate to provide a large “reserve” capacity. We “commission” them at 0.5 times the ASHRAE rate and give control to the occupant. In our experience, the occupant is more intelligent on setting acceptable ventilation rates specific to them than the members of the ASHRAE 62 committees.
It seems like we’re splitting
It seems like we’re splitting hairs here. Too much effort is placed on making good homes better instead of making bad homes acceptable. There are a LOT of bad homes that REALLY need IAQ issues addressed, the good homes are OK as-is for the most part.
Bob:
Bob: Blower door tests and whole-house mechanical ventilation don’t happen in a high percentage of homes in most places. If a home is getting certified in a program like ENERGY STAR or taking advantage of weatherization dollars from the government or utilities, that’s where it kicks in.
Lance: Yes, 1.5x the ASHRAE 62.2 requirement…with control given to the homeowner. It would almost never run at that rate. I don’t think the infiltration credit is of much use. See Joe’s comment here for more.
Michael B.: I think the title of the article is pretty good actually. I agree that we might be able to use a blower door in some cases to see if a home is too leaky to bother with ventilation…yet. I think Dale and Joe addressed your comments about correlating blower door numbers with natural infiltration. Yeah, we might be able to get a decent correlation over a longer time average, but ventilation requirements apply over a short time scale of hours.
Dale S.: All good points! Yes, it would be nice to have MV in all homes, but we do have to consider budgets.
Larry: Sounds like you’re building good homes!
Ted K.: Yep. IAQ and buildng tightness are two different things.
Joseph L.: Thanks for jumping in here. Your statement that “the air change rate from hour to hour or day to day does not correlate to a blower door number” is the main point here. There’s no sane way to accept an infiltration credit of 11.8 cfm, for example, once you understand that.
Bob (again): I disagree that we’re splitting hairs. Understanding how to make good homes better also helps with making bad homes acceptable. Yes, we have to adapt methods and materials, but understanding the fundamental building science here helps all homes.
Hi Joe-
Hi Joe-
As much as I hate to disagree with you, I’ve got a few issues with your reply.
Joe wrote ” The correlation between a blower door number and average infiltration over a year is pretty good if there are no large pressure induced effects by mechanical systems.”
Yes — but in the leaky homes I’m talking about, this isn’t an issue.
Joe wrote “There is a huge leap required to take this “average yearly infiltration” information and use it as a proxy for determining acceptable ventilation rates in houses for heath reasons. To do so requires a belief that average annual exposure is the appropriate metric for health reasons. I believe that that is incorrect and that the appropriate exposure metric should be on the order of hours not a year. ”
I agree that the annual average infiltration rate doesn’t have the same impact on IAQ as a constant air change rate would. Varying driving forces means varying pollutant levels for a given source strength. But I disagree that hours is the right timeframe for assessing this — I think something more like a day would be a fine measure. One hour concentrations really matter mostly for acute poisoning such as CO — but I think CO detectors are better suited for these events than bathroom exhaust fans. In fact, exhaust ventilation might actually increase the likelihood of such an event occurring in the first place.
For many pollutants what we care about is the number of hours per year that concentrations exceed certain levels (although for some pollutants such as radon we really do care mostly about an annual average). This distribution of concentrations will be strongly correlated with the blower door result (for a given home and source strength). Adding a fan can shift this distribution of pollutant concentrations by a lot for tight homes but has very little impact on leaky homes.
Also, if you really care about a few hours of low air change rates then you should not allow a single bath fan to meet the standard — air change rates in bedrooms with closed doors at night are often very low.
Joe wrote [some of my responses in brackets]: “If you accept this [MB: I don’t] then a blower door is not the approach to take for reasons that are quite obvious since you don’t know the size of the hole [MB: yes, that’s what the blower door measures] , the location of the hole [MB: same is true for exhaust ventilation – if make-up air is your reason for concern here] or the pressure difference acting across the hole. Therefore the air change rate from hour to hour or day to day does not correlate to a blower door number. Our tracer gas work and many others has shown this repeatedly. ”
I disagree. Yes the air change rate varies from hour to hour and day to day but it is still correlated with the blower door number. There will be far more hours of very low air change rates in tight houses than leaky houses.
Joe wrote: “We recommend “sizing” systems at 1.5 times the ASHRAE rate to provide a large “reserve” capacity. We “commission” them at 0.5 times the ASHRAE rate and give control to the occupant. In our experience, the occupant is more intelligent on setting acceptable ventilation rates specific to them than the members of the ASHRAE 62 committees. ”
That sounds good (and the last part is catchy) and I actually agree with the general approach — but mostly because I think 62.2 over-ventilates most homes and that odors and other things detectable by occupants are pretty well correlated with IAQ concerns. But I don’t see how you can like this approach but think having a few hours of low air change rates is unacceptable. If you are really worried about CO poisoning or the many other pollutants that don’t smell, then how can you think the occupants are better at determining ventilation rates than the standard committee? Do most occupants monitor multiple pollutants? Is it safe to rely on the correlation of odors with other pollutants? If so, can’t we just have people open their windows when it’s smelly or stuffy during mild weather with low driving forces?
I think if there are resources available in a weatherization program to spend on improving occupant health, safety, and IAQ (beyond basic combustion safety testing, smoke alarms and CO alarms) that those would be better spent on radon testing and mitigation in high radon areas and other efforts at reducing pollutant source strength than on adding fans to homes that are quite leaky. But, just to be clear, I’m not against adding fans to homes that are fairly tight. It’s just a matter of where we draw the line.
I just wanted to be sure
I just wanted to be sure people were aware of this study by ECW
http://homeenergyplus.wi.gov/docview.asp?docid=22505
where they measured CO2 and humidity as indicators of IAQ in weatherization homes that had fans installed under 62.2 (with infiltration credit and actual occupancy not BR+1) and then they turned the fans on and off every week or so to assess impacts. These were generally tight homes. Some of the key findings:
“Poor indoor air quality in the absence of mechanical ventilation was generally correlated with the factors used in ASHRAE 62.2 to determine the need for mechanical ventilation. Generally, tight homes and homes with higher occupancy density had higher humidity and CO 2 levels. This suggests the current ASHRAE 62.2 based protocol does help provide useful screening in determining the need for, and amount of, mechanical ventilation based on
measured air leakage and occupancy level. ”
So, they found that blower door measured tightness was well correlated with IAQ and was a valuable tool for determining whether a fan was needed.
“Operation of the mechanical ventilation improved indoor air quality in most homes where
it was installed. Indoor humidity and CO 2 levels both showed statistically significant declines in most cases when the mechanical ventilation was enabled. The strongest predictor of the magnitude of the reduction was the amount of mechanical ventilation provided in relation to the estimated natural ventilation rate”
In other words — if the fan was large relative to the ACHnat estimated from the blower door it had a much bigger impact on IAQ. So the fan didn’t help much in leaky homes.
” CO 2 levels remained high in a number of homes, even when mechanical ventilation was enabled. Mean CO2 levels were often higher in bedrooms than in living rooms, which may be an indication of poor air mixing”
So a bath exhaust fan doesn’t necessarily lead to much improvement.
They also concluded: “The data from this study suggests further limiting the installation of mechanical ventilation to homes where the estimated natural ventilation rate is less than 30 cfm per occupant would help
mitigate the installation of mechanical ventilation where it is not needed and is unlikely to have much impact”
In other words, you could use the blower door test result to decide that some homes don’t need to have a fan added — specifically based on the estimated natural ACH vs. occupancy.
There’s lots more interesting stuff — highly recommend people read it if they are interested in this issue. Wisconsin weatherization treats lots of homes that are pretty tight.
I think that using an exhaust
I think that using an exhaust ventilation systems such as an bathroom fan is a dumb idea for a controlled ventilation system.
I think that you have no idea what the pollutants of importance are. I think that I might not know either.
I think that leaky houses are not the issue.
I think that you have no basis for asserting that a day long average is appropriate. That is your opinion. My opinion is different and equally as valid. No data exists. No epi studies have been done. I think I am better looking and therefore my view is better. In the absence of data this is all total speculation. I am willing to admit that. Are you?
CO2 and humidity are not good proxies for good air quality. They are better than nothing. But not much better.
The study you cited is total nonsense. No epi studies were done. None have in fact been done. This has all been guess work. No health studies exist. No baselines have ever been measured.
RH and CO have almost no connection to health. The work has not been done. This is all total BS and I do not mean “building science”. Cold climate work via surveys does not have any connection to Houston.
Joe-
Joe-
I agree with pretty much everything you just wrote. We don’t really know nearly as much as we should know. All we can do is make out best guesses based on available science.
The ECW study provides some data about IAQ — but I agree it doesn’t measure IAQ itself because we don’t know how to do that. But it does track some proxies and the findings make general sense.
Do you have hard data that shows we should spend $800 to install a fan in house that leaks 2000CFM50 (or 4000 CFM50?) because the health benefits are not only worth it but also greater than other ways those funds could be used? I would guess, based on your last post, that you don’t think such evidence really exists.
So why should anyone follow 62.2? Maybe because it represents the best guesses of the people on the committee and we should trust them? But the standard has changed multiple times and will change in the future so maybe the current version isn’t really right? Hmmm.
Let me back up a little and go after the whole hourly variation issue. For arguments sake, say I agree that we really care about hourly air change rates. So, how variable do we expect these hourly air change rates to be? Well, it seems like it would be a reasonable first cut to look at using an hourly infiltration model with hourly weather data (TMY3) to estimate how air change rates vary due to varying driving forces. I did a few quick calculations (using all 1,020 TMY3 stations).
I assumed a 2000 sqft two story home with 3 occupants (83 CFM ventilation requirement) and calculated hourly infiltration for a few different leakage rates. Since you set your ventilation systems at half the ASHRAE target air flow, I thought it would make sense to assess how often we expect the hourly infiltration rate to be below this same 50% level. If concentration spikes are the real concern, then we might only really worry about hours when the infiltration rate is less than half this level — implying double the concentrations.
In the first scenario, I assumed the leakage rate was on the cusp of the infiltration credit — 2000 CFM50 — which is not far from a common post-retrofit value in many cold climate retrofit programs.
The analysis estimates that the hourly infiltration rate will be less than the 50% target rate about 5.8% of the time — although 90% of those hours occur when you could open windows (daily average between 65 and 75) and if people can adjust ventilation systems maybe they can open windows. The infiltration rate was below 25% of the target level in 0.7% of the hours. There are very few hours with extremely low infiltration rates as the stack and wind effects are rarely both near zero. Looking at milder climates, just 10% of the TMY3 stations show more than 10% of their hours below the 50% threshold — but those climate would, appropriately, have smaller infiltration credits
A house at 3000 CFM50 is estimated to have just 1.8% of the hours with infiltration less than 50% of the target rate and 0.3% of the hours below 25% of the target rate. Very low hourly infiltration rates are pretty rare in houses that leak 3000 CFM50.
But if the house was 1000 CFM50 (fairly tight, but not extreme) then the estimate is that 43% of the time the infiltration rate will be less than the 50% rate and 5.8% of the time if will be less than the 25% rate. There is a huge difference here compared to the leakier homes. Infiltration rates less than half the ASHRAE threshold would be very common.
I think mechanical ventilation would be a good idea for the 1000 CFM50 house. But I don’t think you can say the same for the house at 3000 CFM50 and you could certainly argue not at 2000 CFM50 either.
This modeling exercise was meant to show that driving forces don’t go to zero very often and homes that are fairly leaky will have very few hours with infiltration rates lower than the rate that Joe is setting in homes. The definition of fairly leaky should vary with climate — as the infiltration credit does.
You can quibble with many of the details, but I think the overall point is pretty solid — blower door test results can and should be used to help decide whether and how much ventilation is needed in homes. Leaky homes usually don’t need added fans and wouldn’t benefit much from them anyway (especially the types of fans people are using). The debate should be over defining how leaky and the infiltration credit is a good idea — but it may need tweaking.
sorry this is so long…
Leave it to you, Michael, to
Leave it to you, Michael, to do “a few quick calculations (using all 1,020 TMY3 stations).” I do agree that it’s pointless to add mechanical ventilation to really leaky homes because the intentional air is swamped by the infiltration air. Then the question becomes, what is the threshold where we need to add MV. And is a blower door result all we need to set a threshold?
I think the kind of modeling you just did could be a good start to setting a threshold, but we need more information as well. Does the house sit on top of a moldy crawl space or basement? Is there an attached garage? Are there combustion appliances inside the building enclosure? We shouldn’t give credit for infiltration without knowing something about the kind of air infiltrating into the house.
Allison- yes, all good points
Allison- yes, all good points. The last thng you want to see is people leaving holes between the house and garage so that the house doesn’t end up “too tight” (I’ve actually seen this). The same potential problem also affects exhaust only ventilation — there’s no guarantee that the fresh air is fresh. There aren’t any easy answers that aren’t expensive, especially for retrofit. It would be great if we had those large scale health studies to help guide the choices.
p.s. computers are fast, running hourly infiltration calcs for 1020 weather stations takes just a couple of minutes.
I think the modeling is wrong
I think the modeling is wrong. You have to guess at the distribution of the openings and pressures. So your percentages are bogus in my view.
Having said that the real question is why spend $500 to $800 dollars on a blower door test? That is the waste.
It appears to be necessary to appease the Cult of the Blower Door.
Go back to my original ASHRAE article or my post on my website for the basis for this view.
I think ASHRAE 62.2 makes no sense for existing homes.
I think that old existing homes are not the problem.
Boy, I hope you guys figure
Boy, I hope you guys figure this one out before my HPWES program has me following 62.2-2013 pointlessly in a few months!
Question – I do a fair amount of work on largish (4000-6000 sf) newish (1990-current) homes that have 90+ furnaces venting to the outdoors. If one of these gets too tight according to BAS (which I think is just a made up number), does it actually matter? 4 people living in 48,000 cubic feet with a .22 ACHN shouldn’t really matter, should it? These places still have blower door numbers in the 3000-5000 cfm50 range.
Measuring CO and humidity is
Measuring CO and humidity is not a good indicator of iaq? I don’t see a large jump between a reduction in two substances known to be contained within indoor air and a realization that other substances are being removed as well.
Does anyone know of a substance that remains in indoor air, while CO and humidity are being vented out?
If no one has a legitimate answer to that question, the ECW study is valid. If you can think of one, I’d like to hear it.
We can split hairs as to what percentage number should be used, whether it be 1% or .001% of the time but otherwise it seems to be a valid study.
Joe L.: In
Joe L.: In your article that I linked to above (Just Right and Airtight), you wrote, “They use a blower door to help measure leakage, and this is also great.” When you talk about the ‘Cult of the Blower Door’ in your most recent comment above, I assume you’re referring to the tendency of some people to overstate what they can do, not that they shouldn’t be used. It also looks like you’re saying that when you’re working on a tight budget, it’s better to eliminate the blower door test than the mechanical ventilation system. Right?
Nate A.: Yes, the BAS is just a madeup number. If you really want to determine if a particular home needs mechanical ventilation, test the indoor air quality. If you’re not working under the guidelines of a program (like Home Performance with ENERGY STAR), you can decide on your own when it’s a good idea to add MV. A blower door might be helpful for deciding on a threshold, but as I mentioned in my last comment here, you need more info than that. Also, the whole point of this article is to try to break people of the habit of trying to relate natural air changes estimated from a blower door test to mechanical ventilation needs.
Scott: Joe just left the 2 off and his comment, which should have read, “RH and CO[2] have almost no connection to health.” And they don’t. Yes, they’re important things we want to control in a home, but IAQ is about much more than those two components of the air. CO, VOCs, formaldehyde, radon, and mold spores are some of the major indoor air pollutants that affect health, and the ECW study didn’t look at the effects of MV on those at all.
You also asked, “Does anyone know of a substance that remains in indoor air, while CO and humidity are being vented out?” Ventilation is not going to remove 100% of any pollutant. We have different reactions to different pollutants at different concentrations. Just because the ventilated homes they studied found reductions in RH and CO2 doesn’t mean that the bad stuff that might have been there went down to safe levels.
Joe wrote:”I think the
Joe wrote:”I think the modeling is wrong. You have to guess at the distribution of the openings and pressures. So your percentages are bogus in my view.”
I certainly agree that the modeling was more an exercise than super precise — but the general results are probably not that far off — in very leaky homes you will rarely have infiltration rates near zero because the lack of temperature difference and wind isn’t that common in most climates. The stack effect is actually pretty well known and the variations in the distribution of openings has a fairly small effect on stack infiltration. In general, the lack of knowledge of leak location is an overblown source of uncertainty. The real problem with infiltration modeling is not knowing the site-specific wind.
Joe said:” Having said that the real question is why spend $500 to $800 dollars on a blower door test? That is the waste.”
This would be true — if a blower door test cost anywhere near that. A blower door test costs about $50 — that’s the incremental cost of adding a blower door test to a site visit from a contractor that was going to be there anyway (the cost is lower for weatherization agencies using in-house crews). The $50 is based on actual bids. The blower door test can also help lead to more effective air sealing.
Joe Wrote: “It appears to be necessary to appease the Cult of the Blower Door.”
Well, if the test weren’t pretty cheap and useful, i would agree. But I would agree that there are many cults in our field: the cult of the duct blaster (which is expensive and not very useful in my opinion), the cult of overly complex building energy modeling, and maybe the cult of complex combustion safety testing (which may have gone overboard)
Joe wrote: “I think ASHRAE 62.2 makes no sense for existing homes.
I think that old existing homes are not the problem.”
OK — maybe we agree more than it seems. I completely agree that new homes need ventilation systems and many existing homes do too.
Michael B.
Michael B.: How precise do you think your results are? I doubt that it’s at the level you indicated with your decimal (5.8% of hours with <50% ventilation met by infiltration, for example). Would you say 6% +/- 5%? +/- 10%? More?
Also, as I pointed out above, I don’t think it’s tremendously useful to talk about infiltration without also looking at where that air is coming from. If it’s from moldy crawl spaces or attached garages, it shouldn’t count at all toward any kind of infiltration credit.
Finally, if a contractor is charging $20 for a blower door test, they’re making up for it somewhere else because they probably can’t even carry the equipment from the truck to the house for that price.
Speaking on behalf of the
Speaking on behalf of the cult of the blower door, I would just like to apologize for the recent statements made by Brother Joseph. He has been under a lot of strain lately. We have dispatched re-education specialists to BSC to help him through this period of troubles.
Bless you and your flow exponents
Allison wrote:”How
Allison wrote:”How precise do you think your results are? I doubt that it’s at the level you indicated with your decimal (5.8% of hours with <50% ventilation met by infiltration, for example). Would you say 6% +/- 5%? +/- 10%? More?”
I didn’t indicate any level of precision, I just tend to use 2 figures for most answers — even if they are rough. The purpose of the results was for roughly comparing between homes of different leakiness — and for that purpose it made sense not to round 5.8% vs 1.8% vs 0.3% (round to zero?). The difference between 43% and 5.8% is large even if uncertainty levels are pretty high.
The exact numbers don’t matter much. In fact, even if we knew the exact air change rates of homes we still wouldn’t know in most cases which would would have bad air quality. Pollutant source strength tends to dominate when it comes to big IAQ problems — until you get to very low air change rates. All we can try to do is try to affect the likelihood of problems — we can’t control them.
I agree with your comments about where the air is coming from — and the same problem is true if you add an exhaust fan. In fact, adding an exhaust fan may make it much worse than relying on natural infiltration as you depressurize the home and suck more air out of the garage or crawlspace. In terms of the infiltration credit, I could see counting it as zero for homes with attached garages and maybe even homes over crawlspaces that haven’t been isolated form the living space.
In terms of blower door test costs — the $20 figure was based on having a low income weatherization agency crew person include a blower door test during their visit. The equipment amortizes quickly and the actual labor time should be less than half an hour per job. You might know it, but there are weatherization agencies installing condensing furnaces for $2000 and sometimes less (including the cost of the furnace) and doing dense pack of walls for less than $1/sqft and doing air sealing for less than $500. The $50 figure is based on an incremental cost for performing a large number of energy audits with vs. without a blower door test. I’m sure it varies between contractors and bids. I’m not at all saying that you could hire someone to come to your home and perform a test for anything near that. But that would be a waste of time.
Doug – I’m not an expert but
Doug – I’m not an expert but my understanding of the issue is in the answer to this question: what is the path of the ventilation air? In relying on random leakage, you get air going through dust, alergens, mold, etc., in a random volume (the blower door test does not normally give each room’s flow rate, nor any indicator if this flow rate happens “naturally”). In relying on manual intervention (AKA opening a window) you need to depend on the residents’ ability to properly judge which windows to open and for how long (assuming they are even home when ventilation is required).
In relying on automated/mechanical ventilation the ventilation air enters through intake points avoiding outside pollutants, goes through a filtration system, and travels through dedicated duct work into the house.
It is always better to provide individual room ventilation through automated/engineered means rather than relying on random leakage or manual intervention.
Thank you so much for
Thank you so much for providing us readers with the Super Bowl of home performance. Any chance we can take a shot at summarizing where everyone agrees. No doubt, there are disagreements here, but I also read a lot of overlapping ideas. I’ll take a stab it but maybe Joe, Michael and the rest can correct me.
When choosing a ventilation system or deciding if one is needed you should know:
1) How leaky the house will be after air sealing. Generally speaking the leakier the house, the less need for mechanical ventilation
2) What the probable cast of IAQ pollutants are in any individual home
3) If the pollutants known or suspected can be reduced, separated from the house or removed all together
4) That exhaust ventilation can be satisfied without dealing with underlying IAQ problems such as moisture and radon
5) That exhaust ventilation can increase IAQ problems if the path of least resistance leads to a polluted area like the garage or to the soil
6) That supply and balanced ventilation can be too expensive for many projects
7) There are alternative ventilation methods not being considered by the HP community in this country.
OK, tear it apart; just remember I am hoping for agreement and overlapping ideas. Thanks, Hap
All I can say is WOW! I think
All I can say is WOW! I think we need to invent a device that gets installed in all new homes that measures pollutants and when it senses high level pollutants it turns on mechanical ventilation. Now the question is do all new homes need some sort of Ventilation ready duct or device that can be easily integrated or turned on when needed like our cars being bluetooth ready? We need to get the manufacturers invloved like, Panasonic, Carrier, Lennox and Broan to help us create and bring these products to market.
Carry on Boys!
I don’t often look at blogs,
I don’t often look at blogs, but was referred to this thread.
I believe that it is clear that a blower door is a useful tool in figuring out whether to install mechanical ventilation. There is no question at all that the precision of the blower door at estimating natural infiltration is, shall we say, inexact. You can’t tell the difference between 56 cfm and 62 cfm of natural infiltration (even on an annualized basis) with a blower door. On the other hand, as Michael says, if the house is leaky enough then it is a valuable tool for telling you not to bother. Given that very few people go to houses to ONLY do a blower door test, I think Michael’s estimate of $50 is quite reasonable for many programs that are in the house anyway. If they are getting paid $500 then they are making $1000 an hour – I’m going to stop training and start doing four blower door tests a week and go skiing. This $50 is well spent if it lets you identify major bypasses to target for sealing and at the same time make a decision of whether you should spend $700 or more on mechanical ventilation.
There are a lot of questions about how well 62.2 matches the actual IAQ issue at a house. Of course it will often be incorrect. That is a problem with any prescriptive standard, whether it be 62.2, the building code, LEED, or anything else. The point of a prescriptive standard is to provide something that will be good enough to address the major issues most of the time. Sometimes you miss. Sometimes you overdo it. If you don’t like the prescriptiveness and want to do something performance-based, please do. The 62.2 standard clearly allows for that, but you do need to actually measure a range of pollutants. It is probably cheaper to do both the blower door test and install a MV system than to do the tests for contaminants.
Also, the standard now allows a path by which a temperature-based control can adjust the ventilation rate. There is discussion of making something like that more explicit, but you can do it now. There is an alternative to the prescriptive rate that essentially allows you to do something else if it meets the same goal as the prescriptive intent.
I don’t understand when people say that 62.2 is for new construction and not existing buildings. What is an existing building but a building that used to be new? Once there are occupants, and walls, and contaminants, isn’t ventilation an issue? Maybe ventilation isn’t an issue for homes with only walls and contaminants, but no occupants, but I figure that most homes we go to have occupants. So then we should think about ventilation. If 62.2 is trying to provide enough to address major problems most of the time, that seems to be a good target for homes, especially those that exist. Then you use the blower door to get a sense of whether you need a fan at all (leaky houses even after air sealing – in Illinois weatherization the average starting value is about 3900 cfm50 which means there are plenty that start well above that and stay “leaky” even if we get 60% of the leakage before the money runs out), reduced (semi-leaky) or at near full 62.2 rates (tight). Then, because people need more clarity than “none, reduced, or full” we stick numbers to it. Where do we get these numbers? From another prescriptive standard, the one that turns blower door results into infiltration estimates. Just like the 62.2 flow rates are based on assumptions of “typical” contaminant levels, blower door-based infiltration estimates are based on “typical” leakage distributions and sheltering, etc. Which means, of course, for any individual house your mileage may vary.
Two an hour, eh? $1,000 an
Two an hour, eh? $1,000 an hour, eh? Apparently you have never run a business.
Try it once. Market the service. Get the referral. Contact the occupants. Set up the job. Travel to the side. Do the test. Write the report. Pay for the insurance. Buy the equipment. Service the equipment. Cover your overhead.
Then add the concept of “test in” and “test out”. And understand the “true believers” don’t trust the folks actually doing the work. That means third party testing – mostly to appease the HERS mafia.
$20 my ass. $50 my ass.
Join the real world. Try to buy this on the “free market” instead of just legislating it and subsidizing it and pretending that real costs don’t matter.
I stand by my “real costs”.
When you factor in the real costs can you than appreciate the other alternatives which are safer and cheaper and more reliable….except in the government subsidized regulated world.
Joe- the $50 is a real price
Joe- the $50 is a real price based on contractor bid. I didn’t claim this was the price for a special visit to just do a blower door test – that would be a waste of time and money. This price is how much more it costs to add a blower door test to an energy audit. All of the other costs you mentioned are already incurred, you are simply adding the time for running the test and having the equipment. It does not add $500 to the cost of any energy audit to include a blower door test.
Micheal, I’d have to agree
Micheal, I’d have to agree with Joe, he is better looking.
But here’s a present for you… 12,559 HPwES jobs over the last two years in new and old versions of excel:
http://bit.ly/blowerdoorfoil &
http://bit.ly/blowerdoorfoilOLD & for those who like pictures:
http://bit.ly/nyHPwESbdpercentage
CO2 as proxy really makes me uncomfortable. It’s ventilating long after occupancy, possibly providing the freshest air after the occupants leave.
Yep, hours not years.
Just have them open windows? Really?? Any fallback to opening windows is absurd. An open window with no pressure differential provides no fresh air.
Joe get’s my vote for smarter and prettier.
And assuming leaky homes leak uniformly may lead to some catastrophic problems. How leaky is the bedroom, and what ACH is it seeing relative to the total ACH? Drill down and the problems with the assumptions go OFF THE HOOK.
Michael, I begrudgingly love the information you provide, but have real problems with some of the huge jumps you make to your conclusions. Intuitively they are the things my college statistics professors warned AGAINST.
Measuring bedrooms seems spherical cow. It’s probably the highest occupancy room, the smallest volume, and the least air circulation as occupants are inactive (People moving tends to move/mix a lot of air).
DO NO HARM – I think the desire to make doctors obsolete for physicals is centuries away. The patient needs to be seen.
I think the same is true for buildings. I see the data guys want to make building diagnostics unnecessary, but whenever you do you often cause significantly more harm than good.
Guess I’ll read the second half of the responses…
Again Allison, you continue to outdo yourself. It’s gonna start getting hard to keep one-upping your prior blogs.
Joe,
Joe,
I love my blower door. If there is one thing I think is a critically important tool, that is the one.
I’m open to being shown a critical path to delivering home performance to homeowners that doesn’t lie about how much of the project will be subsidized by the energy savings. I don’t think that happens without a blower door.
I am not confident I could do it, but if someone can show me a way to do it that makes the time and client education it offers unnecessary, I’m willing to learn.
Crap, did I just agree with Micheal B? Now my hit counts will go down…
NO!!
NO!!
“1) How leaky the house will be after air sealing. Generally speaking the leakier the house, the less need for mechanical ventilation”
NO!
“I believe that it is clear that a blower door is a useful tool in figuring out whether to install mechanical ventilation.
NO!
“On the other hand, as Michael says, if the house is leaky enough then it is a valuable tool for telling you not to bother. ”
YES!!!
“I think we need to invent a device that gets installed in all new homes that measures pollutants and when it senses high level pollutants it turns on mechanical ventilation. ”
Look, I genuflect to my blower door before going to bed. But I never assume what it tells me is proxy for whether people have good IAQ.
I’m in a friends incredibly leaky house in Oakland right now, and I’m pretty sure it has IAQ issues. (Wish I had a blower door and airadvice)
http://bit.ly/HEREARESOMENUMBERS
Why do we need blower doors?
Why do we need blower doors? Because without them no air sealing occurs.
http://bit.ly/nyHPwESbdpercentage
It is a quality control tool.
It’s a proxy for energy savings. It’s a proxy for whether energy savings promise will occur.
And when I’m done, it will be a competitive metric driving incentive to ever improve quality in home performance. It will be JD POWERS for home performance contractors.
It will also inform what is likely and possible, so people know when they can improve.
TRACKING MATTERS – Bill Gates says just the act of measuring causes polio cases to drop in African Nations. The premise is operators use tools more effectively when they know their success, and their failure, will be open to public scrutiny. Carrot and stick. I believe the same is true for energy which is why I’ve been digging for these numbers. Taking a common phrase one step further; Measuring Causes Management.
What you don’t measure you can’t manage. We can measure leakage, and we need to manage it.
http://bit.ly/HEREARESOMENUMBERS
http://bit.ly/nyHPwESbdpercentage
Joe asks “Why do you
Joe asks “Why do you even need an energy audit?” That is a fair question, one that I think should be asked once in a while. Here are a few reasons why:
1) Not every home needs attic insulation
2) Not every home is leaky
3) Some homes need different insulation (like in walls)
4) Duct problems?
5) Many/most contractors haven’t learned the building science enough to figure out a lot of things (though they could usually tell whether the attic insulation was insufficient, I’ll agree there); I certainly don’t trust a lot of them to figure out where the big leaks are since they aren’t usually staring them in the face from the living room
6) Trust – many/most people don’t trust the person who would do the work to be honest about what work is needed, especially when many people really just want new windows; the energy audit is a way to get a homeowner to better believe what is needed
Things might seem straightforward to those of us on this discussion, but there aren’t enough of us to go around.
Ted’s “NO, NO, NO, YES
Ted’s “NO, NO, NO, YES” comment…
You misunderstand me. I said “generally”. Whenever we have a prescriptive standard, like 62.2 or the codes, we are talking about the general case. Same for using a blower door to get a sense of whether you need mechanical ventilation. ASHRAE 62.2 sets rates for typical conditions, and is quite explicit that it does not guarantee good IAQ because there can be more extreme conditions. Sounds like your friend’s house may have some of those.
For the GENERAL case I think the blower door can be useful to say if you need mechanical ventilation. You have a house that is 30 ACH50? You probably don’t. A 60 cfm fan will be in the noise. Get the house down to 15 ACH50? Likely the same result.
But for the SPECIFIC case? The 30 ACH50 house is a meth lab? No amount of ventilation will save you, including all 30 ACH50’s worth of natural infiltration. Have 30 dogs that you never let out for bodily functions, or a room full of mold? Not the general case again, and even the leakiest house won’t be enough. Ever been to a farm? You are in the wide open and it still stinks.
Ted is right, a blower door test is not a proxy. You should not just assume. You should not turn your brain off once the number has shown up. Same is true for combustion. Have a natural draft water heater and a 1000 cfm downdraft kitchen exhaust (or a big return duct leak) in a 3 ACH50 house? I don’t care if the water heater venting is correct. Just because the code says you have adequate venting does not mean the water heater will draft properly.
Sometimes a leaky house will have an IAQ problem. Sometimes the solution might even be mechanical ventilation instead of dealing with the source. We should use the blower door with our brains, not instead of our brains. Doesn’t change the fact that in many cases the blower door can be a good indicator that adding mechanical ventilation is irrelevant.
“6) Trust – many/most
“6) Trust – many/most people don’t trust the person who would do the work to be honest about what work is needed, especially when many people really just want new windows; the energy audit is a way to get a homeowner to better believe what is needed”
Nuts, wish I’d written that…
I think it beats Joe’s line:
“the air change rate from hour to hour or day to day does not correlate to a blower door number.”
For most important idea in the replies.
until we have room by room
until we have room by room blower doors, I have to agree with joe. I myself live in the leakiest farmhouse you can imagine. I can feel wind coming through my floorboards in my over-ambient-crawlspace-living room in the winter. significant wind! There is no doubt whatsoever a blower door would say we don’t need ventilation. and in the ground floor, it would be absolutely right. It’s also true that we will never have moisture problems in this farmhouse in maine.
However, upstairs in the master bedroom, air quality is not the same. there is one door in and out. there isn’t anything magic that makes that air mix at any particularly high rate to the rest of the upper floor, and what infiltration there is is drawn through cavities that likely contain mouse poop, dead bugs and other appetizing things.
By the way, the house will be listed soon, am I selling it??? anyone want to bid???
the point is that air quality can vary dramatically from room to room within the same house, ESPECIALLY the bedrooms, where we all spend about a third of our lives!
I’ll even note we built a shop recently with a small server room that I never installed a door on. a year after we stopped smelling paint in the rest of the exquisitely ventilated shop (super tight, ultimateair ERV), you could still smell it in there. again… “natural” exchange through doorways is not a given. at least it’s not a given to any adequate level.
1. you have to exhaust baths.
2. you have to supply fresh air to bedrooms through some clean route.
once you decide that these two things are valid, it’s kind of a no brainer to run a little duct and use a balanced ventilator. because you can’t do both of these things much more cost effectively any other way. you can do timed bath exhaust and airlets I suppose, in the bedrooms. I hope someone is watching exhaust air pathways through the home in that case of course. ducts seem to be the only reliable way to do it.
will not having fresh air in my master bedroom kill us? no. it won’t. but what is the cumulative effect of stuffy and perhaps somewhat allergenic air?
the answer is: some value of not good. different for different folks in different situations. Until quantified, shouldn’t we advocate for playing it safe??
A few people seem to be
A few people seem to be misinterpreting my points. I have never claimed that all leaky homes will have good IAQ. I also think that satisfying 62.2 by adding a continuously operated bath fan will not guarantee IAQ. Even a balanced distributed ventilation system can’t guarantee good IAQ, but it can work much better than the alternatives — at a considerable cost, especially in retrofit.
My comments have been about whether it makes sense to add a bath fan to a leaky home as some sort of IAQ solution. I just doubt that’s a good blanket recommendation and I’m pretty sure Joe and Paul both agree with me on that. I think we can help define a leaky home using a blower door.
We can’t guarantee good IAQ, we can only shift the likelihood of problems (do no harm means do nothing ever). I think adding a bath fan to a leaky house has very little impact on that likelihood and I haven’t seen any data or engineering analysis to indicate otherwise.
p.s. I’m really glad Ted disagrees with me, because he is wrong so often I’d have to worry if that weren’t the case.
“5) Many/most
“5) Many/most contractors haven’t learned the building science enough to figure out a lot of things (though they could usually tell whether the attic insulation was insufficient, I’ll agree there); I certainly don’t trust a lot of them to figure out where the big leaks are since they aren’t usually staring them in the face from the living room
6) Trust – many/most people don’t trust the person who would do the work to be honest about what work is needed, especially when many people really just want new windows; the energy audit is a way to get a homeowner to better believe what is needed”
Paul is absolutely correct. And I’d add an ammendment to #5: most work done by builders/remodellers is too shoddy for general acceptance. This is the reason blower door tests are valid. New houses versus old? We’ve seen shoddy work in both, and if 80% of the housing stock needed in 2030 already exists today, the problem is much larger than new construction.
I’d also partially agree with Michael – you need to ventilate baths, but not for IAQ reasons. You need to get rid of the moisture – regardless of the rest of the house’s IAQ.
I would also (slightly) disagree with Robert “once you decide that these two things are valid, it’s kind of a no brainer to run a little duct and use a balanced ventilator. because you can’t do both of these things much more cost effectively any other way.”
Cost effective? I don’t think so. Not with today’s cost of technology; and especially in retrofit. How about positive-pressure supply to each living space? Hospitals do it all the time to ensure that all the nastiness EXITS the room versus coming in. Much less cost than installing a HRV/ERV and not much of an efficiency hit (at about 70% efficiency rating for the ERV’s/HRV’s air flow). Just provide supply to every living space and engineer some 1.5x ASHRAE 62.2 exit points
(if the “natural” ventilation will not allow the flow).
the incremental cost of
the incremental cost of adding a few exhaust ducts and upgrading to an ERV is, at that point, generally justifiable, at least in a new construction environment. Maybe $1k-$1500 duct and $500-$1k fan unit depending on quality chosen (and potentially with efficiency far exceeding 70%), without concern for forcing moisture into the inevitable leaks in your building cavities and rotting your house to the ground. If that replaces bath fans, and garners high efficiency exchange, and improves comfort…
In a retrofit I agree the costs are higher and that is problematic, but I don’t think I’ve ever seen a retrofit in a cold climate that I’d suggest supply only ventilation for. maybe as a part of a Deep Energy Retrofit, but retro to existing housing stock? That would seem… risky, at best.
What’s the best way to make
What’s the best way to make five hundred bucks doing a blower door test? Start with a thousand dollars of time, then add some expensive tools.
Re: infiltration vs size-of
Re: infiltration vs size-of-the-hole vs MV/ERV requirements.
How about using the blower door to measure CFM50 with all windows and doors closed, and then opening a window by a measured amount (say equal to one square foot), and seeing how much the CFM50 changed. By doing some arithmetical gymnastics (I am not a mathematician, so I don’t know exactly how you’d do it), you can come up with a relationship that translates to ACH or something you can base MV / ERV sizing on.
Allison, you said to just
Allison, you said to just have the indoor air tested. I am having trouble finding a testing company that will do all: VOC’s (especially formaldehyde), mold spores, particulate.
I agree with Joe Lsttiburek
I agree with Joe Lsttiburek blower doors are over sold, and i know they certainly “suck” but they do quantify a before and after. How they relate to Natural Air Changes, is less “natural”! We like to retrofit tight and ventilate right , in the relatively dry climate of Denver CO a humidity gauge helps us, humans (and pets) create indoor humidity cooking, showering, watering (pets and plants) and breathing. I believe in getting humidity between 30% to 50% for our interior goal. I hope my thoughts are not all wet, especially when I am known for my dry sense of humor and 38 years of learning from doing retrofits,