Replies

1. 
   homedesign | Oct 10, 2012 05:43am | #1

   N factor is a correlation factor used to estimate "Natural" air changes per hour when the Blower door ACH(50) is known

   ACH(Natural) = ACH(50) / N

   
2. GBA Editor
   Martin Holladay | Oct 10, 2012 05:49am | #2

   The N-factor is the number by which you divide your ach50 number in order to estimate so-called "natural airflow," or ACH(nat).

   It varies from 9.8 to 29.4. It cannot be determined by climate zone alone; it also depends on the number of stories in the building under consideration. (See the image below, which was taken from http://www.ybshadesofgreen.org/files/helper-pdf/Module8-_FINAL.pdf).

   For more information on the N-factor, see What is the N-Factor?

   
3. GBA Editor
   Martin Holladay | Oct 10, 2012 05:58am | #3

   John,
   It looks like we were posting almost simultaneously ... you beat me to it. Thanks.

4. Expert Member
   Dana Dorsett | Oct 10, 2012 11:08am | #4

   That's the definition, but it's a VERY squishy number, difficult to impossible to measure in-situ. An ACH/50 test number measures the combined size of the leak holes, but tells nothing about the leakage location or distribution, and those factors matter (a lot!) when it comes to the real infiltration rates.

5. 
   homedesign | Oct 10, 2012 11:30am | #5

   Dana,
   I agree ACH-50 (and N-factor) tell us nothing about how the "openings" relate to or interact with the Neutral Pressure Plane, the prevailing winds,human intervention and or mechanical effects.

6. 
   jwolfe1 | Dec 30, 2021 11:59am | #6

   Almost decade after the last post and I found this to be very helpful. Thanks!