Insight these folks as little more than charlatans who run around - PDF document

Insight—053 Just Right and Airtight tends to be more satisfying than getting a gun. I view Insight these folks as little more than charlatans who run around for the sake of the show, rather than providing value to the process. If you are using a blower door for this reason, it makes more sense to take the money spent on Just Right and the tester and the blower door and spend it on a ventilation system and combustion safety. 2 I know I won’t win this argument because there is too much Airtight money involved in the show and managing the show, but I can get satisfaction in calling something “bull#@%!” when I see it. An edited version of this Insight first appeared in the ASHRAE Journal. By Joseph W. Lstiburek, Ph.D., P.Eng., Fellow ASHRAE Folks are building houses and retrofitting existing houses with increased airtightness, and this is great. They use a blower door to help measure leakage, and this is also great. 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. A blower door measures a characteristic of the house, not the leakage rate of the house in service. You can’t use a blower door to determine air change rates because a blower door does not give you the distribution of holes, and if you don’t know the distribution of holes, you can’t determine the pressure differences across them during service. If you don’t know both the distribution of holes and the pressure Photograph 1: The Ubiquitous Blower Door —I love what differences across them, you don’t know jack. 1 Never it can do and hate what it can’t do even though people say mind that I love blower doors, and that I use them all of that it can. That is pretty clear, isn’t it? the time. Read on. Blower doors measure equivalent leakage area. Not the When someone puts a decimal place into a blower door- real leakage area and not the real leakage paths and determined air change rate after a whole bunch of certainly not the distribution of the real leakage area and computer-assisted numerical manipulation, and the real leakage paths. Everything is sort of combined proclaims that the interior environment in a house is safe into a single near meaningless value. Not a meaningless without a ventilation system and without a provision for value, but a near meaningless value. The real meaning, in combustion air, I usually go have a bourbon because it 2 You can install a ventilation system and code-compliant combustion air for 1 I have always wondered who “Jack” was. Turns out it is not a “who,” but a less than $500, which is about the cost of a blower door test. Then, you “what”: “a trifling, infinitesimal amount.” The other word that usually follows don’t need to do the blower door test and the computer-assisted numerical “jack” does not need to be defined as most folks already know what it is and masturbation. some of us can recognize it. September 2011 www.buildingscience.com 1

Insight—053 Just Right and Airtight Photograph 2: Bathtub on Exterior Wall —The classic “Joe Photograph 3: Fireplace on Exterior Wall —OK, an even Hole”—a hole so big even I can crawl through it. It needs to be bigger hole than the bathtub hole. Kind of makes it funny to draftstopped with something rigid and airtight. Note to folks out think about sealing an electrical wire going through a top plate there in the real world: fluffy insulation is not rigid and airtight. when you have something this big. But a sheet of OSB or gypsum board over fluffy insulation makes the fluffy insulation happy and Joe happy. my not so humble opinion, is that it can tell you when you get rid of the big holes 3 and that is where I am going with this. We are going to focus on big holes and a great use for a blower door. Blower doors are a quality control thing. But they are not the only quality control thing. They are one of many. And they are not always necessary despite what folks say. What they are not is a quality assurance thing. The difference is important. Quality assurance is figuring out what the right thing to do is; quality control is doing it. For example, the right thing to do is to “build tight and ventilate right.” Blower doors can help measure the Photograph 4: Soffit on Exterior Wall —Wow, this allows for “tight” part. They cannot measure the “ventilate right” connecting your entire floor cavity to the outside. part. reliable than any other approach—such as building a To me, the ventilate right part is easy: put in a ventilation leaky building with random uncontrolled holes. And in system and pick a rate. 4 A ventilation system is more terms of the rate, let the people in the house pick the rate much like we do with letting people pick a temperature. We give them a system that can satisfy a range of 3 For the folks who say you need a blower door to find the big holes I also say “bull“#@%!” Give me an experienced contractor and I will match them conditions, and then we give them control of the against a geek with a blower door any day. And when you find a big hole thermostat. I say we do the same with a ventilation stat. and fix it you don’t need a blower door to tell you that you fixed it. Take a picture of the fix and put it in a file. There is your proof, if you need proof. Most of the time I spend with blower door geeks consists of explaining to So how tight should we go? Depends on who you ask them how come they haven’t found the big hole yet and where it actually is. 4 Our approach is to design and install a controlled ventilation system that is and whether or not they are crazy. 5 capable of ventilating at 1.5 times the current ASHRAE Standard 62.2 recommended rate, commissioning the system at 60% of the current ASHRAE Standard 62.2 recommended rate and giving control of the off the heat completely as things will freeze. Also, most of us can sense ventilation system to the occupant and telling them they can turn it up, turn temperature; we know when it is too hot and when it is too cold. Ventilation it down or turn it off. They are responsible for their own environment. This is a little bit different. It can be argued that most people don’t know when personal responsibility thing is big with us. Of course, there are folks who they have enough ventilation or when they have too little. I like ranges. A want to control your thermostat, and folks who are going to want to control range of ventilation rates that fit between the bookends of too much and too your ventilation stat. I say, we hunt these people down and get them out of little. We can set the “bookends” from a policy perspective and then get out the gene pool. Just my opinion, mind you. Apparently, elections have of folks’ way. consequences. Before I get a zillion comments, I know it is not quite the 5 Disclaimer here: I know that I am crazy. same. Most of us know that there is a safe range for temperature: don’t turn 2 September 2011 www.buildingscience.com