I really like blower doors.There are a lot of building diagnostic tools that most people have probably never heard of that I like. Duct-blasters and flow plates to name a couple of more. For readers who are interested in conserving energy who haven’t heard of a blower door, check out Martin Holladay’s article on blower doors here.

Blower doors are primarily used to quantify a home’s leakage at a fixed pressure. That pressure is nearly always 50 Pa. This allows us to do two important things:

  1. Make comparisons with other houses. When people ask the question “How leaky is my house?” they usually mean “How leaky is my house with respect to other houses?
  2. Track changes – hopefully reductions – over time.

We can do a lot of other things with a blower door. But we shouldn’t care nearly as much about zone pressure diagnostics as we do about the big picture stuff above.

I run a blower door several times a week, and have worked on the shells of hundred of homes. My crew has had tremendous success at making buildings tighter. One of our earliest discoveries when using a blower door is that it’s pretty much useless at ‘directing’ air-sealing. This is very much counter to conventional wisdomin most energy geek circles, so let me lay out my case against blower door guided air-sealing.

  1. We can’t multi-task very well (thanks Daniel Kahneman!). So either we’re operating a blower door or we’re air-sealing the house. We can’t do both at once.
  2. The fact that a small area of air-sealing hasn’t yielded much benefit doesn’t mean that subsequent air-sealing won’t, and vice versa. Suppose we scamper down to check blower door results having completed 1/4 of an attic only to discover that the numbers haven’t changed much. Does it follow that the remaining 3/4 of the attic shouldn’t be sealed? Of course not! If we succumb to dejection we will never get results. Get back in the attic and finish the job!
  3. Traveling back-and-forth from the work site to the front door is time-consuming. Specifically it takes time away from the important work of air-sealing.
  4. Blower door tests run sporadically throughout the workday are probably not very accurate. Occupants or workers will often open and close windows and doors, thereby rendering test numbers useless.

My comments aren’t directed at energy efficient new construction, i.e. homes so tight you can use a fog machine to pinpoint minor leaks.

The implications of my argument makes the task of air-sealing existing homes fairly simple. Start with the accessible stuff up high (attics), then low (basement and crawlspace rim joist). Once the other stuff becomes accessible (exterior walls through a re-siding project or vaulted ceiling through a roof replacement) make it tighter. Run a blower door test at the start and finish of each project.

Now get back in the attic!


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