The Blower Door

Well, it has been another couple of weeks of not much excitement around here, except for two things. We did get a favorable ruling from the Zoning Board of Appeals, so things on the permitting front are moving along. We now have a 21 day waiting period during which time our neighbors can raise their concerns. Our neighbors are pretty much unconcerned about what goes on over here, so I don’t foresee any problems in that regard.

The other piece of news is that the nice folks from the Building Science Corporation (BSC) came to our house to perform the pre-construction blower door test. The BSC functions as National Grid’s technical adviser for the DER program, so they are the people that pick the proposed projects apart to make sure they are going to work, and inspect the projects to make sure the construction details are being implemented properly. The pre-construction blower door test gives us a measurement of the amount of air leakage through the existing building shell, and that value will be compared to the leakage after the construction is complete to see how we did. So yes, there will be a test.

For those unfamiliar with a blower door, it is a specialized fan that accurately measures the volume of air that flows through it. To prepare for the test, all the exterior doors and windows are closed, and the fan is put in a shroud that fits tightly in the door jamb. The fan is hooked up to a computer that measures the flow of air though the fan, the interior air pressure and the exterior air pressure. The computer’s software then controls the fan to create a pressure differential between the interior space and the outside. The rate of air flow through the fan is then an accurate measurement of the amount of air infiltration through the building shell, at a specific pressure differential. The air pressure is typically measured in pascals (Pa), and the volume of air flow is typically measured in cubic feet per minute (CFM).

So how did our house fair? Well as expected, it is leaky. It measured 2,185 CFM @ 50 Pascals, that is 2,185 cubic feet of air passed through the fan per minute at a pressure differential of 50 pascals. That is a lot of infiltration. The target we are trying to reach set for by National Grid as part of the DER is 413 CFM @ 50 Pascals, less than a fifth, so we had better start finding those air leaks.