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Blower Door Testers Wanted – Scientists and Engineers Preferred

Blower Door Test Resnet Hers Standards Engineer Statistics

blower door test resnet hers standards engineer statisticsOK, the title here may be a little extreme, but if you’ve taken a look at the new chapter on performance testing and scope of work in the HERS Standards, you know what I’m talking about. RESNET just adopted this as the new chapter 8 in August of this year, and it goes into effect on 3 January 2012.

OK, the title here may be a little extreme, but if you’ve taken a look at the new chapter on performance testing and scope of work in the HERS Standards, you know what I’m talking about. RESNET just adopted this as the new chapter 8 in August of this year, and it goes into effect on 3 January 2012.

As a physicist, I love the new rigor they’ve added to the protocol for doing Blower Door tests. If you ever took an introductory physics class and the associated lab, you probably remember with great fondness the statistical analysis you had to learn. (What!? You hated that part? I just don’t get you at all!)

Anyway, measurement is a science in and of itself that follows some fundamental rules:

  • Every piece of equipment will give you a measurement with some uncertainty.
  • Measuring something once doesn’t give you the absolute, final, correct result. 
  • To improve reproducibility, the measurer must pay great attention to the conditions under which they make the measurement.

With the new standards on Blower Door testing, RESNET is acknowledging that these rules apply to home energy raters as well as the folks who wear white coats. (Actually, I call the latter chemists. Physicists mostly just wear whatever they want.)

So, what’s new for all you Blower Door testers out there? Here’s a brief summary.

Three types of tests

Single-point test. Measure the air leakage one time at a given pressure difference, usually 50 Pascals. You have to measure the baseline pressure 5 times, but that doesn’t take long.

Multi-point test. Measure the air leakage at multiple pressure differences, from 60 Pa down to 15 Pa in 5 Pa increments. You’ll have toblower door test resnet hers standards engineer measure the baseline pressure difference before and after taking the air leakage readings, but you don’t adjust for the individual pressure readings.

Repeated single-point test. Measure the air leakage at least five times at a single pressure difference and then do a statistical analysis of the results. Calculate the mean, standard deviation of the mean, and uncertainty.

Two types of accuracy

Standard accuracy. Under normal test conditions, you’ll get results with an acceptable level of uncertainty. You can use the result in a certified home energy rating, and the software doesn’t modify it. When doing a single-point test, if your baseline pressure difference is less than 5.0 Pa, you’re in the realm of standard accuracy. For a multi-point test or repeated single-point test, you get to report the result here if the corrected cfm50 has an uncertainty less than 10%.

Reduced accuracy. On really windy days or when other conditions cause your uncertainty to be too high, you report the result as having reduced accuracy. If you’re doing a certified home energy rating with reduced accuracy, the software will add about 10% to the result to determine if the home complies with the thresholds required in energy codes or programs. If the baseline pressure difference is between 5.0 and 10.0 Pa for a single-point test, you’ve got reduced accuracy. (If the baseline is >10.0 Pa, you can’t do a single-point test.) For a multi-point test or repeated single-point test, an uncertainty of more than 10% means the accuracy is reduced.

Two corrections

Altitude. If you’re doing a Blower Door test at high elevations (that is, anything higher than 5000 feet above sea level), you’ll have to apply a correction factor to your air leakage. (Yeah, they’re talking to you, Steve Byers and your Energy Logicians!)

Temperature. If you’re testing on a really cold or a really hot day, you’ll have to adjust for that, too. When the temperature difference, ΔT, is greater than 30° F, you must adjust. (See the tables on page 8-9.)

As I said above, I see the new rigor in the HERS Standards as a good thing. It may take some retraining of the field guys who go out and do Blower Door tests all day long, but it’ll be worth it. We’ll be adding these new procedures to our training starting with our next HERS rater class. If you do any type of performance testing under the auspices of the HERS Standards, you don’t have to be a scientist or engineer…but you’ll have to start thinking like one.


Related Articles

Infiltration Occurs at the Surface, Not in the Volume

It’s the Hole – Understanding What a Blower Door Is for

Georgia Rocks! – New Energy Code Requires Blower Door Test


Download the HERS Standards

This Post Has 23 Comments

  1. I have always run a multi
    I have always run a multi point test. I like the validity provided by the test compared to a single point. 
    I believe you tweeted something from a session at Joe’s Boot Camp this summer about ‘no temperature correction’ and other info about multipoint tests. Is that something that works into these comments or is that another blog post?

  2. You know, I bought a Retrotec
    You know, I bought a Retrotec manometer so I wouldn’t have to worry about all this stuff. I like the fact that there is a computer inside that is making those statistical calcs for me. Now what do I do?

  3. At the beginning of my first
    At the beginning of my first semester of what was called Physics for Engineers (calculus-based) in college, we spent the first few weeks focused on nothing but the art of data collection, error estimation, error propagation, and how to graph stuff. We even did a bunch of labs focused on nothing but that, in order to build solid experimental skills. When we finally started actually studying physics, we did so with a set of solid, core empirical skills. I bet an equivalent short curriculum would likewise benefit anyone learning home performance auditing, in the same way. Consider developing something like that, Allison! 🙂

  4. John N.: I
    John N.: I’m going to do another post in the near future about multi-point vs. single-point testing. Whereas the former may give you greater precision, greater accuracy doesn’t automatically go along with that. 
    Arlene: Yes, the Retrotec manometer is great, but you’ll still have to decide when your results get entered with standard accuracy and when they go as reduced accuracy. The Standards also make it pretty darn clear how to set up and run a Blower Door test to help ensure that your rating provider (FSEC in your case) will have the best chance of reproducing your results.

  5. Clearly, the equipment mfrs
    Clearly, the equipment mfrs will need to update their software, hardware and user manuals to comply with the new standard.  
    It will be interesting to see how much of the decision tree they can spare the technician from having to deal with. For example, since these manometers measure “gauge” (relative) pressure and not “absolute” pressure, it would be helpful to add an absolute pressure sensor (barometric) to automatically determine the elevation. Likewise with temperature.  
    Presumably a smart manometer would be able to determine uncertainty based on fluctuations in the baseline pressure. 
    I’m not as familiar with Retrotec’s manometer, but DG-700 users, short of a major h/w upgrade, would need to use a laptop or perhaps smart phone during testing. 
    All of this is speculation of course, but I agree with Allison that RESNET cannot expect technicians to use their own ingenuity to comply with the new rules. 
    One thing about multi-point testing… this method is simple and quick, and is more accurate than using a conversion formula (especially conversions using a generic “n” factor) to get to CFM-nat or ACH-nat. However, if your testing protocol or software requires ACH-50 or CFM-50, then multi-point buys you nothing.

  6. Allison< /
    Allison< />: I just read your reply to John N. Just to clarify, my reference to higher accuracy for multi-point was only referring to it’s ability to estimate infiltration at natural air pressure, as compared to a conversion formula. The intrinsic uncertainties of the blower door readings themselves are still there.

  7. John P.:
    John P.: You’re right. It’s time for people who do this kind of performance/diagnostic testing to know something about data analysis. If we do that with partial differential equations, would you take the class?

  8. Hi, 

    Souds like the folks that make up this stuff have never met an HVAC contractor. 
    Accordingly, since infiltration rates can be affected by the house next door, if the house has a fence, in a valley, on a hill, seasons, in the rain, on a train, in a box, with a fox,should we measure all this too! I do like these green eggs and ham. Sounds like the scientist’s are out of hand.What all do you want us to measure Sam I am! Sounds like a jobs program Sam I am.  

  9. David B.:
    David B.: I agree. Smart manometers will make complying a lot easier, and Blower Door operators need it to be easy. Also, you’re spot on with the limitations of multi-point testing when the software wants only a single-point result (cfm50). 
    Phil J.: Yeah, I can see how it might seem like the “scientists are out of hand,” but if I’m handing out a $2000 tax credit or writing $5,000 in energy improvements into a mortgage and those amounts depend on a Blower Door test, I’d like someone operating the Blower Door who knows the difference between precision and accuracy, and who knows how to achieve both.

  10. Won’t the Energy Conservatory
    Won’t the Energy Conservatory’s TecTite software run a multi-point test with the outcomes to meet the new standard?

  11. Kevin V.:
    Kevin V.: Yes, you can use TecTite to run the multi-point test, as described in the HERS Standards. Until you get a ‘smart manometer’ that can also tell you the temperature and elevation, you’ll still have to collect those data manually, though, as well as make the call about whether your accuracy is standard or reduced.

  12. I think you have
    I think you have misunderstood the standard and the comments show further misunderstanding. In developing this standard (i was on the committee that developed it) the goal was to make it easier to do a compliant test by allowing standard one point tests using the “cruise 50” setting on the gauge – the calculations are built into the smart gauges that come with the equipment. Rather than require altitude and temperature adjustments for all tests, the standard let’s you ignore the altitude unless you are at more than 5000 feet and you can ignore temperature at less than 30F dT.  
    The baseline pressure readings should take just 1 minute to ensure that it isn’t extremely windy – just 5 consecutive readings from the 10 second averaging setting. In 99% of the tests, you’ll be fine and be able to claim standard accuracy.  
    I don’t understand your description about using the highest result for the adjustment in the single point test 
    p.s. multiple-point tests are pretty much useless in my opinion because the flow exponents of houses are almost all between .60 and .70 and the measurement uncertainty is significant compared to the true variability – so if you actually find an unusual flow exponent in a multipoint test you probably have a bad test.

  13. Michael B.
    Michael B.: You’re right about what I said about the baseline measurement, and I’ve changed that in the article. I’m not sure what I was thinking when I wrote it, but it certainly wasn’t correct.  
    Regarding my possibly misunderstanding the standard, I don’t think I’ve done so, at least not in the way you implied. I don’t think I said anywhere in the article or comments that the new procedures would be onerous (though I did say smart manometers would make complying ‘a lot easier,’ which could imply that I think it’s really hard, I guess). Perhaps you were inferring that I meant only scientists and engineers would be able to do it? If so, please read that last line: “…you don’t have to be a scientist or engineer…but you’ll have to start thinking like one.” 
    Yes, you’re right that the temperature and elevation corrections won’t apply to all tests, and I stated that in the article. I didn’t say anything about the prevalence of standard vs. reduced accuracy, but I also agree with you that most tests should fall under the former category. The main point of my post was that the HERS Standards are more rigorous now, and raters, providers, and trainers have to adjust their practices. 
    I appreciate your comment, Michael!

  14. Allison- 

    It appears that you are still misunderstanding how the standards have changed. The testing standards have become simpler, easier, faster, and require less statistical analysis and less rigor overall.  
    Perhaps you aren’t familiar with what the standards actually required prior to this change? They required following ASHRAE 119 section 5.1 which references two testing methods — ASTM E779-87 and CAN/SGSB-149.10-M86. Both of these testing methods are far more rigorous and complicated with more requirements and statistics than what is now allowed by the new standard.  
    The new standard was developed to officially sanction simpler testing methods because the prior standards were more appropriate for researchers than production testing and required far too much work for little gain in accuracy (do you know that the standard required pressurization and depressurization testing with the results averaged?).  
    The reality is that few (if any) testers were actually following these standards — even those doing multi-point tests using a laptop. The new standard has less stringent requirements and provides more options — including an officially sanctioned approach for simple one point tests using the cruise@50 feature found in newer gauges.  
    So I think the title and content of your article are off base — the standards have actually changed from very complicated and time consuming to much simpler.

  15. Michael B.
    Michael B.: Now I see the source of your comment, and I plead guilty on that one. I’m one of the many who wasn’t following the standard referenced in the HERS Standards. When I went through the HERS class in ’03, my training provider didn’t cover it. When I worked for them teaching HERS from 2008-10, we never even mentioned it. We taught the students the method as described in the Blower Door manual and the steps called out in App. A of the HERS Standards. 
    You admit that “few (if any) testers were actually following these standards,” and that’s my sense, too. I wonder if any trainers actually taught their students about the details of ASHRAE 119 section 5.1. Since most teach a 5 day class, my guess is that no one did. 
    I understand your objection to this article now, Michael. Thanks for pointing it out. Yes, relative to the actual standard raters were supposed to be using, the new standard is easier. Relative to what most have been doing, though, I still contend that it’s more rigorous, though not necessarily more time-consuming. Further, I think we both agree that it’s a great improvement, no matter how you look at it.

  16. Allison – 

    Allison – 
    I figured that was the case — not many people actually looked up those standards even though they were supposed to follow them. So I can understand how the new standard can look more complicated than the old — we’ve now incorporated the entire testing procedure into the RESNET standards rather than reference external complicated standards. 
    I’m curious what you consider to be current common practice among raters when doing a blower door test — do they use a temperature correction? do they do automated multi-point tests using a laptop? do they do one point CFM50 tests without any corrections or anything? I guess this uncertainty is one of the main reasons for creating the new standard.  
    It’s not easy to create a testing standard that is specific and defensible without it looking very complicated. I think that trainers like you, after reading the new standard carefully, will recognize that it’s actually now pretty easy to just do a one point “official” CFM50 test and you will come up with easy ways to teach the standard.  
    HERS software providers will need to make some changes to deal with the 2 levels of accuracy, but it seemed like a good trade-off compared to just forbidding testing under windy conditions.

  17. Michael:
    Michael: Good questions. I can’t answer for the whole country, but I think here in the Southeast, most raters are doing single-point tests and not applying corrections. I don’t know if there’s any place here that’s high enough for the elevation correction, and we do almost all of our testing with less than a 30° F ΔT. Florida does require multi-point tests, but I think most of the trainers in the other Southeastern states do single-point. I’ve talked to a trainer in another part of the country who said they’ve ignored the ASHRAE 119 standard, too. They said even their lawyers agreed it wasn’t reasonable for doing in the field.

  18. Retrotec is putting on a
    Retrotec is putting on a Webinar on this topic that might help but for now, the idea of the RESNET procedure is that you don’t need to use a computer necessarily. If folks want it done in software, let us know and we’ll make it happen.

  19. I am liking my Retro-tech
    I am liking my Retro-tech more and more each day. The software (Fan-Testic)compensates for altitude and temp, it also gives a confidence interval. It comes standard with a multi-point test feature ( up to 10 tests at varying predetermined pascals)

  20. OK, did some checking. Good
    OK, did some checking. Good news is we are on it as we do all of our BD’s with TecTite. Bad news, we haven’t been proactive in getting the word out past our staff and some Rater Partners. One of our ace staff members, Glenn Pease, tore the new standard apart back in August and brought up all the details. As we use TecTite, the discussion didn’t go further.  
    On the topic of what we train, etc. We don’t train to comply with 119 or especially 779. They simply aren’t practical in the field, especially 779. So, hang us up by our toenails, but I will buy the beer for anyone who tells me they do a 779 compliant blower door test in the field. As for what to train, yes, be aware of what the standard says, but to train 119 or 779, no way. We see that as part of our “Go Deeper” activities, but not part of the base training.  
    This brings up the eternal conundrum all trainers face with RESNET, BPI, LEED, etc. – when the standard changes and the test doesn’t change we are stuck teaching the “old” way because that’s what the test will reflect versus the “new” way which is what will have to be done for the current state of any given program. Sigh.

  21. Sorry for the lack of detail
    Sorry for the lack of detail above. For EnergyLogic, all of our tests are above 5000’AGL. Lots of them are greater than 30 degrees dT.

  22. I have recognized the
    I have recognized the problems with ASTM E-779 and when I proposed the large building testing standard, the method bypassed those problems so you could get stable results under any weather conditions. 
    Since then I have written a detailed paper where I tested the same building over a million times by chopping up the mass of data collected for different time intervalsa and compared the results. A new test method emerged that I am currently campaigning for adoption by ASTM and ISO. I am giving a presentation on this next week in Brussels and hope to talk with Max Sherman of LBL about it as well. Bottom line is that the new RESNET procedure uses some of the techniques I mention in my paper.  
    If anyone wants a copy of the USACE test protocol or the paper, send me a message to 
    I am trying to make it easier to get consistent results and save time by not doing things that don’t count.  

  23. As always, a significant
    As always, a significant article.I have just had a house built. The test was 0.8 and then on completion it was 0.8ac/h@50pascals. Frankly, I don’t believe the second test as air entry control was not as easy nor as rigorous as the initial test. Multiple measures would clarify this situation.Anyways the test is an indicator only and not related to whether you have a cat valve or not.The test should be done with people living in the house and then the variability would be profound.Cheers Mike Legge

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