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What's Wrong With This Picture?

Posted on Feb 11 2010 by Carl Seville

This is just a brief rant about a photo I ran across today. While I was working my way through the USGBC's required online training modules in preparation for a two-day green-rater training class at RESNET this month, this picture appeared in the section describing blower door testing. The training is obviously designed to provide information to a wide range of professionals, from the least to the most experienced. Being the impatient type, I zipped along as quickly as possible through the areas that I knew well and spent more time on those that I was less familiar with.

But this picture really got my attention. Maybe I'm just being picky, but if you're trying to explain a blower door test to someone, why show them a picture with the fan completely covered? I don't think I even have the disk that covers the center of my fan; and while I suppose it might help protect the fan motor, the other side is completely open all the time, so how much difference can it make anyway?

I wonder if people will be confused, annoyed, or amused, or just not notice anything strange about this picture when they see it. Maybe I just need to get a life.

Feb 11, 2010 10:38 AM ET

Maybe it is Cold Outside?
by John Brooks

The technician decided to "close the barn door" and not waste the homeowner's Energy while he set up his equipment and while the photographer took his picture.

Feb 11, 2010 10:40 AM ET

Hi Carl, I am not familiar
by Gavin Healy

Hi Carl,
I am not familiar with this picture or the trainning. There are a few circumstances where the blower door is configured this way. Because it is already set up it is a convient reference port to the out side which is useful for a number of pressure diagnostic test. The one I use most frequently is the air hander is turned on and I check if the house pressure goes negative or positive, idicating supply or return dominant duct leakage. At the same time I agree that the picture would show off the blower door better if the fan was exposed.

Feb 11, 2010 10:44 AM ET

Thanks for the feedback
by Carl Seville

Always interesting to find other's take on a subject.

Feb 11, 2010 4:35 PM ET

by John Semmelhack


Yes, the picture is not the best for showing a blower door in action. However, the cover is an essential part of setting up for a blower door test. A proper blower door test starts with measuring the baseline pressure difference between inside and outside. This is done WITH THE COVER ON! Once an accurate baseline is established, you can "zero out" the baseline pressure difference in order to measure only the pressure difference caused by the blower door fan.

If you want to do accurate blower door tests, I suggest you find your cover...or at least tape off the opening so you can get a baseline reading.

Feb 11, 2010 4:44 PM ET

Baseline pressure
by Carl Seville

Interesting point, John. I recall that being brought up in any of my trainings. Learn something every day.

Feb 11, 2010 4:45 PM ET

by Carl Seville

Meant to say I DON'T recalled that being brought up in training.

Feb 12, 2010 12:08 AM ET

I am not kidding
by Danny Kelly

All of the above comments a very good points and they are all correct, however I agree with the basis of your article. I actually met a guy the other day that was bragging about his greatness and his new LEED-AP Status but did not even know what a blower door was. Makes you wonder.......

Feb 12, 2010 1:29 PM ET

You're doing it WRONG
by Anonymous

I'll echo this comment. "A proper blower door test starts with measuring the baseline pressure difference between inside and outside. This is done WITH THE COVER ON! Once an accurate baseline is established, you can "zero out" the baseline pressure difference in order to measure only the pressure difference caused by the blower door fan."

Find your cover, because you're doing it wrong! Maybe the picture is perfect because some raters don't know how to setup a blower door before you start the test.

Feb 12, 2010 7:25 PM ET

To John & Anonymous
by Carl Seville

I appreciate the feedback on determining the baseline pressure. I will have to do an informal poll among raters I know to find out how many people actually do this when they test out a house.

Feb 14, 2010 7:54 AM ET

Odd slide choices
by Tom Brudzinski

Your point is well made, Carl. Way too many times people use slides in presentations that either disprove a point or confuse it. I sat thru a "Greening Preservation" talk the other evening given by knowledgeable, experienced people. Still, they used a slide that showed a really sorry housewrap installation (wrong-way laps, etc.) . I guess most people would not have noticed, but the presenters should have!

Feb 14, 2010 10:55 AM ET

Training on baseline
by Allison A. Bailes III, PhD

I took the same HERS class at Southface that you did, Carl, but a few years earlier. I also took the Home Performance with ENERGY STAR class there, and I think maybe that's where I first met you, since we were in the same class in '05. In neither of those two classes did the instructors cover adjusting for baseline.

I found out about it by reading the manual after the class, but only sporadically did I do the baseline adjustment for my Blower Door tests. Here in the Atlanta area, we have little wind, so most of the time our baseline is only a pascal or two. Given the fluctuation in the results of the BD test, it hardly makes a difference, especially for leaky houses. On windier days or on a cold day with a tall house, neglecting the baseline adjustment can skew the results significantly.

I don't know why Southface didn't teach this procedure for such a long time, but you and I and a lot of other people have gone through classes there without learning it. I've been teaching the HERS class there for the past two years now, and we finally added that to the training in the middle of last year.

I think part of the problem here is that we try to teach raters and building analysts too much material in too short a time. Then we send them out on their own to figure it all out. The industry is so young that in many parts of the country, the newly trained can't go out and work with experienced companies who help fill in the missing pieces for them during an apprenticeship period.

Allison A. Bailes III, PhD

Mar 3, 2010 1:55 AM ET

Baseline/Multi-Point Test
by ijustinj

We typically haul out the laptop, connect it to the blower door setup and conduct a multi-point test via TECTITE. When starting the test, you are always prompted to cover the fan to get a baseline and, when the test is finished, cover it again to get a final baseline.

At the end of the day, I don't think it matters one way or another if the picture shows the fan covered or not. The USGBC prep for their test doesn't train you to do diagnostics or much of anything else building science related. You're basically just learning the LEED book and the relationships behind the sections. Sorry I digress....

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