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What is N-factor?

I was asked by a client -- I'm an Energy Advisor -- what the N factor was for his town requirements, and I didn't know the answer.

Asked by Roland Schoenke
Posted Oct 9, 2012 11:15 PM ET
Edited Oct 10, 2012 4:53 AM ET


5 Answers

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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

Answered by John Brooks
Posted Oct 10, 2012 4:43 AM ET


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?

Answered by Martin Holladay, GBA Advisor
Posted Oct 10, 2012 4:49 AM ET
Edited Oct 10, 2012 10:39 AM ET.


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

Answered by Martin Holladay, GBA Advisor
Posted Oct 10, 2012 4:58 AM ET


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.

Answered by Dana Dorsett
Posted Oct 10, 2012 10:08 AM ET


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.

Answered by John Brooks
Posted Oct 10, 2012 10:30 AM ET

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