Blower Door Test / by Lincoln Brown

Time to catch up on my posts! In early March, insulation was complete and Efficiency Vermont did a blower door test to see just how tight we were. And it is tight. 0.84 ach50. I'm not going to attempt to explain, so please read here if you want to understand!

0.6 ach50 is the golden standard of Passive House certification so we aren't quite there, but we never intended to be. Just getting under 1.0 is quite a feat. 5.0 is considered tight! The building scientist we have been working with, T.J. Holloway, claims he's not seen a house that tight at this stage of construction. It's likely that it will improve more once the sheetrock is in.

T.J. Holloway from Efficiency Vermont, performing the blower door test.

Sub 200 cfm50!


from the above mentioned article:

Is my house tight?

Here are some comparison points to help interpret an ach50 reading:

  • A 2002 study of 24 new Wisconsin homes showed a median air leakage of 3.9 ach50.
  • New home builders in Minnesota routinely achieve 2.5 ach50.
  • The Canadian R-2000 program has an airtightness standard of 1.5 ach50.
  • The Passivhaus airtightness standard — a tough standard to achieve — is 0.6 ach50.

David Keefe, the manager of training services for Vermont Energy Investment Corporation, recently wrote an article on blower-door testing. “Houses with less than 5 or 6 ach50 are considered tight, and those over 20 are quite leaky, though these numbers can be misleading without considering other variables such as climate, house size, and old versus new construction,” Keefe wrote. “Tight houses tend to measure less than 1,200 cfm50, and moderately leaky homes measure between 1,500 and 2,500 cfm50. Homes that measure over 3,000 cfm50 are considered leaky.”

According to The Homeowner’s Guide to Renewable Energy by Dan Chiras, “A really good measurement is around 500 to 1,500 cfm50. The older houses we work on typically fall in the 6,500 to 8,500 cfm50 range.”

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