Students in Massachusetts have to pass the MCAS exam in order to graduate high school; our trial was the the blower door test. How air tight is our house? Was covering every exterior wall with rigid foam, filling the attic and several interior walls with dense pack cellulose, spraying the fieldstone foundation with open and closed cell foam, taping every seam, and emptying untold numbers of cans of foam worth the effort? The blower door would decide.
Blower door design is an ingenious example of turning common objects into more than the sum of their parts. As you can see in the picture to the left the machine is an amalgamation of a calibrated fan and flexible fabric that fits tightly into a door frame. Press a button and the fan sucks air from the house until the pressure difference between inside and outside reads a standard 50 Pascals (Pa)* An airflow meter on the fan measures the amount of air (in cubic feet per minute or CFM) necessary to maintain 50 Pa. A leakier house requires more current to move through the fan to maintain the requisite 50 Pa. As a bonus, the fabric turned our front hallway into a glowing funhouse red.
Waiting for the outcome of the blower door test felt like being in the doctor’s office as you anticipate your blood pressure and cholesterol numbers. You hope for the best while trying to silence your worst fears. As our moment of reckoning approached I calmed myself with the knowledge that Kent, Andrew, and the crew had spent over seven months concentrating on the minutia of sealing the envelope of our house. I remembered the day, on the cold edge of spring, when I came home and found Kent, on his back, squeezing canned foam along the foundation and realized there was nothing to worry about. And then the results: 0.06 CFM at 50 Pa, the best number to date in the National Grid Deep Energy Retrofit Pilot Program.
*A pascal is a unit of pressure named after Blaise Pascal, a Renaissance child prodigy who turned his attentions to the physics of air pressure after inventing the first digital calculator. Had he been born today instead of 1623 who knows how he might have used his prodigious mind power to propel the development of reliable renewable energy.