Effective Leakage Area and Normalized Leakage (Blower Door to Square Inches of Hole)

Effective leakage area converts CFM50 into square inches by fitting the building's leakage curve back to a reference pressure and treating the whole envelope as one sharp-edged orifice -- a single divisor, because that is all the fit amounts to. The US convention references 4 Pa and the Canadian equivalent leakage area references 10 Pa, so the SAME house has two leakage areas differing by about a factor of two, and quoting the wrong one is a frequent source of confused comparisons between reports. Both are reported here for that reason. Normalized leakage adds a height correction, because a tall house drives more stack flow through the same hole than a single-storey house does. That is what makes normalized leakage rather than ACH50 the right basis for estimating natural infiltration, and it is why two houses with identical ACH50 can have quite different real-world air change rates -- the ACH50 number normalizes by volume, which is not what drives the flow. The practical value of leakage area, though, is rhetorical rather than technical, and that is worth being explicit about. A homeowner told their house tests at some number of air changes per hour at fifty pascals has learned nothing they can picture. Told that the house has a hole in it the size of an open window, permanently, in every weather, they have learned something they can act on. The arithmetic is the same measurement; only the sentence differs. This is a conversion of an ENTERED measurement: it does not perform the blower-door test, correct for temperature, altitude or the exponent of the actual leakage curve (the single divisor assumes a typical exponent near 0.65), locate any of the leakage, or estimate natural infiltration, which needs a climate and shielding factor and is a separate calculation. ASTM E779 or E1827, the RESNET or BPI protocol in force, and the rater's own procedure govern.

ELA (US, 4 Pa reference) = CFM50 / 18.9 in square inches, and EqLA (Canadian, 10 Pa reference) = CFM50 / 10.0; specific leakage area = ELA / floor area; normalized leakage = 1000 x SLA x (building height / 8.2 ft)^0.3. The hole side is the square root of the ELA.

The LBL effective leakage area conversion at the 4 Pa reference and the CGSB equivalent leakage area at 10 Pa, both by name, with the ASHRAE Fundamentals normalized-leakage definition and its height correction. The two conventions describe the SAME building and differ only by reference pressure, so a figure quoted without its convention cannot be compared with one quoted under the other.

Two published divisors and one power-law height correction.

Estimate. AHJ and licensed professional govern.

Field names used by the API: cfm50, floor_area_ft2, ceiling_height_ft, storeys, ela_in2, eqla_in2, hole_side_in, ach50, normalized_leakage, sla

• Reference pressure 4 Pa for ELA, 10 Pa for EqLALBL and CGSB conventions
• Height correction exponent 0.3 about an 8.2 ft referencethe normalized leakage definition
• Single-zone envelope the model does not say where the leakage isa zonal pressure diagnostic