Blower door tests

What's a blower door anyway? When building a superinsulated and very air-tight building, blower door testing is conducted to measure air-tightness.  A calibrated fan in conjunction with a pressure testing device depressurizes the the building revealing the level of air infiltration.

A standard system known as Minneapolis Blower Door from the Energy Conservatory uses an adjustable door frame with nylon sheeting within which the fan and pressure gauge are mounted.  Manufacturers of similar systems include Infiltec and Retrotec. Further combined with a smoke pencil or fog machine, the blower door test provides visual evidence of air leakage paths.



To achieve Passive House (PassivHaus) building standard,  air tightness must be less than or equal to 0.6 air changes per hour at 50 Pascals (ACH50).  Pressure gauge output indicated as cubic feet per minute at 50 Pa, or CFM50, can be converted to ACH50 using the following formula:

CFM50 x 60 minutes/hour
interior volume in cubic feet 

Let's compare the allowable ACH50 of several standards pertaining to residential construction:
Passive House <= 0.6 ACH50
Energy Star 3 <= 4 ACH50
IRC 2009 <= 7 ACH50

Note that differences between volume calculated as interior, basement, or minus interior elements such as floor and partition volumes will change the meaning of air-tightness in these standards.  For more accuracy, interior volume should include basement space and subtract interior elements.

Proof is in the pudding.  The blower door test is an excellent diagnostic tool to confirm construction will meet planned or modeled design values or identify gaps that can be addressed before continuing on.

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