A home audit, or energy audit, is a whole house inspection that can usually reveal where and how energy is being lost. Normally, an auditor's job is to inspect the energy efficiency of the home, identify inefficient operating systems, and suggest improvements that should lower utility costs. Basically, there are three types of audits: a simple walk-through survey, a comprehensive air leak test, and a diagnostic screening using specialized equipment.
Normally performed outdoors, a walk-through check is a thorough assessment generally including an inspection of all exterior doors, storm doors, windows, skylights, roof, and siding. Most auditors watch for gaps, poor caulking, and other signs of inadequate weather stripping. Usually, the auditor will take into consideration the building's orientation to the sun and any plants that provide shade or windbreak as well.
Inside, the inspection commonly includes such items as the thermostats and exhaust vents. It is also customary for an auditor to analyze the efficiency of large appliances, such as the furnace, air conditioner, and water heater. In the basement, he will usually inspect the walls, the air ducts, and the wall sills for caulking and proper insulation. In the attic, an auditor typically measures the insulation, checks the attic vents, and inspects other areas that may cause air leakage.
Since the basic home inspection does not require specialized diagnostic testing equipment, a homeowner often can do a simple home audit without professional help. Home audit checklists are normally available from local utility companies, various energy conservation websites, and from government websites, such as the United States Department of Energy. Owing to education and experience, certified energy auditors can usually do a more thorough inspection than unskilled homeowners can during walk-through audits.
In a diagnostic screening test, professional auditors frequently use the blower-door test to measure a building for air tightness. During the home audit, a strong fan is mounted in the frame of an exterior door. As the fan draws air out of the house, the air pressure inside is lowered, similar to a vacuum effect. The outside air pressure then pushes air in through the cracks and openings. Some auditors use a smoke stick to detect air leaks, and others use a calibrated unit with an airflow manometer to check the rate of air return through the unsealed cracks and holes.
Another diagnostic test is the infrared thermography test, which uses a special infrared imaging device called a "Forward Looking Infrared," or FLIR, camera to identify the temperature differences of a home's exterior. Commonly, when there is a distinct difference between the outer air temperature and the inner temperature, this high-resolution thermography is very effective at showing where there is heat transference in the house's outer shell. A thermal-analysis home audit is usually the most expensive audit, but often it is the most revealing of the three.
There is a new energy audit test that is not as common called the PerFluorocarbon tracer gas test (PFT). The Brookhaven National Laboratory invented the test, which uses a perfluorocarbon gas emitter and a gas receiver to measure air changes. As the emitter gives off the gas, the receiver collects it. In this test, the concentration of gas that the receiver picks up indicates the home's efficiency. More gas in the receiver equals a tighter home. The homeowner sends the receiver back to the laboratory for analysis. This test, like the airflow manometer test, does not pinpoint where the air leaks are, but rather gives an overall diagnosis of the building's tightness.