ELA is the whole house leakage area at a pressure difference of 4 Pascals assuming a single flow point with a smooth, rounded area (Discharge coefficient = 1.0).
Above definition is Copyright © The Home Ventilating Institute. Some content originally appeared in John Bower's book, Understanding Ventilation, published in 1995 by The Healthy House Institute.
From HHI:
The size of a single round-edged opening that a house would have if all the small random holes between the indoors and the outdoors were combined into one hole. Used in the U.S. and based on a pressure of 4 Pa. It is the same concept as equivalent leakage area, but is calculated differently.
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