5.1 Air infiltration into the conditioned space of a building accounts for a significant portion of the thermal space condition load. Air infiltration can affect occupant comfort by producing drafts, cause indoor air quality problems by carrying outdoor pollutants into occupied building space and, in hot humid climates, can deposit moisture in the building envelope resulting in deterioration of building envelope components. In cold climates, exfiltration of conditioned air out of a building can deposit moisture in the building envelope causing deterioration of building envelope components. Differential pressure across the building envelope and the presence of air leakage sites cause air infiltration and exfiltration (1).4

5.2 In some buildings, restricting air movement between interior zones of a building may be desired to separate dissimilar interior environments or prevent the movement of pollutants. Although not dealt with specifically in this standard, the detection practices presented can also be useful in detecting air leaks between interior zones of the building.

5.3 Air leakage sites are often difficult to locate because air flows may be small under the prevailing weather conditions. Wind conditions can aid in air leakage detection by forcing air to enter a building; however, where air is exiting, the building envelope construction may make observations difficult. For these reasons, forced pressurization or depressurization is strongly recommended for those practices which require controlled flow direction.

5.4 The techniques for air leakage site detection covered in these practices allow for a wide range of flexibility in the choice of techniques that are best suited for detecting various types of air leakage sites in specific situations.

5.5 The infrared scanning technique for air leakage site detection has the advantage of rapid surveying capability. Entire building exterior surfaces or inside wall surfaces can be covered with a single scan or a simple scanning action, provided there are no obscuring thermal effects from construction features or incident solar radiation. The details of a specific air leakage site may then be probed more closely by focusing on the local area. Local leak detection is well addressed with the smoke tracer, theatrical fog, anemometer, sound detection, the bubble detection, and the tracer gas techniques, however these techniques are time consuming for large surfaces. The pressurized or depressurized test chamber and smoke tracer or a depressurized test chamber and leak detection liquid practices can be used in situations where depressurizing or pressurizing the entire envelope is impractical, such as is the case during construction. Both of the practices enable the detection of very small leaks. To perform these practices requires that the air barrier system be accessible.

5.6 Complexity of building air leakage sites may diminish the ability for detection. For example, using the sound detection approach, sound may be absorbed in the tortuous path through the insulation. Air moving through such building leakage paths may lose some of its temperature differential and thus make thermographic detection difficult. The absence of jet-like air flow at an air leakage site may make detection using the anemometer practice difficult.

5.7 Stack effect in multistory commercial buildings can cause gravity dampers to stand open. Computer-controlled dampers should be placed in normal and night modes to aid in determining the conditions existing in the building. Sensitive pressure measurement equipment can be used for evaluating pressure levels between floors and the exterior. Monitoring systems in high-tech buildings can supply qualitative data on pressure differences.