We did our first blower door test on July 18th. A blower door test is a way of measuring how air-tight (or air-leaky) a house is. Basically, you close up the house as tight as you can except for one door. In the door you put a specialized fan that has an airtight shield around it. Hooked up to the fan is are sensors and a computer that, when the fan tries to pull air out of the house, tell you how leaky the house is.

The standard amount of depressurization that is used is 50 pascals (1 pascal is approximately 0.000145 pounds per square inch). At this amount of pressure the fan was able to pull about 137 cfm (cubic feet of air per minute) out of the house. Correct me if I am wrong, another way of putting this is that after one hour of the fan blowing at this pressure, 2/3 of the air in the house would be replaced by new air. This 2/3 number is actually .68 and is called air changes per hour (ACH).

What does this all mean? It means our house is really air tight. So air tight in fact, that out of hundreds of the homes my friend Matt has tested (including new construction), ours is already the most air tight he has ever tested. I say already because not only do I still need to plug up some electrical penetrations and so forth, but we don’t even have insulation or drywall up yet–which will do a lot to prevent air leakage. What is most exciting for me is that we will probably exceed the German Passive Haus standard for air tightness: .61 ACH.

The blower door test setup.

The blower door test is nice, but actually finding the leaks is better. To do this we flip the fan around so that it blows air into the house. Using a fog machine to make the leaking air visible on the exterior of the house allows you to find where the leaks are. Here, Matt blows fog at a window, a common location for leaks.

It was actually fairly difficult to locate where the fog was coming out. Perhaps we needed a more powerful fog machine. I tried using a line laser to see the fog, but it didn't help at all. Later in the evening, I remembered from reading Theodore Gray's graphic book on elements, that gases do not reflect light, they only inhibit its passage. Therefore, shining a handheld laser away from where one is standing would never work. One would have to shine it at one's eyes, which, of course, is dangerous. I then asked Matt's partner Sarah, to shine a flashlight towards me. Sure enough, it did a great job illuminating the fog. If one does see a "gas" reflecting light back at you, like when you are driving through fog, technically you are seeing a vapor or mist.

Thank you to Matt and Sarah for coming up to help with the blower door test.