Comparison of Blower Door and Tracer Gas Testing Methods for Determination of Air Infiltration Rates Through Building Envelopes at Normal Operating Conditions

Abstract

Tracer gas and blower door testing are two widely used methods to determine the rate of air infiltration through a building envelope. Blower door testing is performed at elevated pressure differentials across the building envelope whereas tracer gas testing is conducted at near zero differential pressures, better reflecting the air leakage rate at near normal building operating conditions. The primary objective of this study was to determine whether extrapolation of blower door test data to normal building operating conditions provides a good estimate of annual average air infiltration at those conditions. Two methods were used to extrapolate the data and were then compared to the baseline tracer gas tests. A secondary objective was to determine the ventilation rate of a residential facility using tracer gas tests. Tracer gas testing seems to be more reliable in determining the air leakage rate at normal operating pressures, but is sensitive to the tracer gas and ambient weather conditions. Regardless, for the subject facility, the ACH50/20 rule and Sherman’s ACH50/N correlation, extrapolated from the blower door tests, are within 6%–33% and 4%–38% of the tracer gas results, respectively. However, these errors are dependent on the assumptions used. Nevertheless, it appears that simple blower door testing can provide a reasonable measure of a building’s annual average air infiltration rate regardless of ambient conditions, whereas the more expensive and complex tracer gas tests may better reflect seasonal variations in air infiltration rates.