Shell blower door test results

Today was the big day. Matthew Evans from Newport Ventures came out to the house to conduct our first blower door test, and the results were very encouraging. Our final reading was 159 CFM or 0.56 ACH.

This was the first of two blower door tests. This first test is used to determine the air tightness of the house enclosure or shell. All plumbing vents and air ducts are blocked for this test. Doing this test before the house is fully insulated makes it easier to find and fix any leaks.  The second test is conducted after the house is finished and is considered the official number.

For this first test we were shooting for 200 to 300 CFM (see earlier posts, How tight is tight enough? and The cost of infiltration). Our initial testing over the weekend using a blower door our insulation installer loaned us gave us a reading in the 250 to 300 CFM range. This was helpful because it allowed us to pinpoint a few areas in the shell that we had missed, the connection of the ERV ducts to the exterior and a few other plumbing and electrical penetrations.

The initial reading from Matthew today was 185 CFM. In order to convert that value to air changes per hour (ACH) you multiply the CFM times 60 and divide by the volume of the house. He had calculated the volume of the house as 16,896 ft(32′ * 22′ * 24′). The resulting ACH is 0.66. If you use the PassivHaus definition of volume (at least the best I can understand) then the volume would be 13,697 ft3 and the ACH, 0.81. So we’re very close to one of the tightest standards for residential homes.

But there’s more.

We had covered all the plumbing vents and air ducts with plastic and tape, but Matthew found a few holes in our tape and lose plastic fittings. So he plugged the two exterior vents and we re-ran the test. The new blower door reading was 159 CFM or 0.56 ACH. (159 CFM was the average over 10 seconds. At the moment I took the photo above it was registering 158 CFM.) By PassivHaus volume standards this would be 0.7 ACH.

To put it mildly, this was better than we could have imagined.

But there’s no time to celebrate, we’re on a schedule. Tomorrow our insulator is coming back to blow more cellulose on the 2nd floor and in the attic, and we have siding to finish and more sheetrock to hang. Not to mention getting our gutter supplier to ship our order. I’m not having a good customer experience at guttersupply.com.

3 Responses to “Shell blower door test results”


  1. 1 Marjorie 14-September-2011 at 10:00 pm

    Yea for tight fittings. ;)

  2. 2 Larry 15-September-2011 at 1:55 pm

    Correction: Paul our energy modeler at DEAP Energy Group, estimated our volume at 12,104 ft^3 using PassivHaus standards, which would bring us to 0.79 ACH@50. If we were trying to certify by the PassivHaus standard, we would have to get down to 121 CFM@50 to meet the 0.60 ACH@50 requirement. Still, I’m happy with our result considering this is our first attempt.

  3. 3 Jim Merrithew 21-September-2011 at 1:42 pm

    Larry,
    You’ve done very well. Congratulation! Jim.


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