ACHn is short for Air Changes per Hour Natural. One of the biggest issues seen by many is that when one uses a blower door to determine how “leaky” a house is, they are applying artificial conditions that one would not see normally.
In order to get ACHn you simply take your ACH50 number & divide it by the LBL factor. The only ones I know of that really even care what this number is now are those attached to programs based on BPI’s 1989 ventilation specs.
