Certain parts of the home, such as garages, attics, and crawl spaces, should be completely sealed from the rest of the house in order to prevent the passage of contaminated air into living spaces. One easy way to test for leaking airflow is to use a theatrical fog machine. This is the same equipment used onstage and in movies to create fog for special effects and can be rented from most theatrical supply companies. Place the unit in the area to be tested, turn it on to fill the space with fog, and then observe the adjoining areas for signs of fog that indicate where leaks must be sealed.
When testing the garage, seal the door and the open vents with tape and plastic to prevent the fog from escaping. The same can be done for attic and crawl-space vents and other
intentional openings to the outdoors. Common air-infiltration points revealed by the fog test include electrical outlets, the juncture where the gypsum board meets the floor, and around poorly sealed plumbing, electrical, and ductwork penetrations. Theatrical fog testing is especially helpful when performed in conjunction with a blower door. This will allow simulation of a variety of adverse weather conditions that may create unusual indoor air quality problems during inclement weather. Be sure to notify the fire department before you begin this type of test; otherwise a wellmeaning neighbor who sees the smoke might dial 911 and set the fire trucks in motion.
Testing for Leakage in Air Distribution Systems A consultant can test for leakage in air distribution systems in a manner similar to blower door testing for a whole house. Doing this testing while the ductwork is still accessible, before it is covered with finishing materials, will simplify repairs. Supply and return registers are sealed off so that the system can be depressurized using a blower door or calibrated fan. The combined airflow through all leakage openings can then be determined. Ideally, leakage should be less than 3 percent. If a small amount of excess leakage is revealed, a theatrical fog machine can be used to trace the sources. If leakage is extensive, it will be necessary to examine all junctures and reseal where required prior to retesting.
