Blower door test: During a blower door test, an energy audit inspector will affix a flexible, airtight door over an exterior door frame, leaving the exterior door frame open. The blower door shroud contains a powerful fan that removes the indoor air, which lowers the pressure.
All of your windows and exterior doors need to be closed, as well as the fireplace flue vent. The point is to close all normal openings and then see where air comes in anyway. It's a good idea to turn down your thermostat during the test to ensure the system doesn't start up due to a possible drop in temperatures.
Once the home has achieved sufficient negative pressure, the inspector will evaluate the home's exterior envelope, looking for sources of drafts, heat loss or air infiltration. This may be performed with something as simple as a smoke pencil, which produces a wisp of smoke used to identify air currents, or something high tech like a thermography scanner.
The Department of Energy's Energy Savers program, which provides consumer and homeowner information about increasing residential energy efficiency, notes that it's important to have a calibrated blower door test performed, not an uncalibrated one.
A calibrated blower door test will use sensors to measure the actual amount of air that's being pulled out of a home, which means you'll get a more accurate interpretation of your home's energy use. An uncalibrated blower door test won't measure the volume of air being pulled from the home, so it can only identify air leaks and not how much potential energy those leaks waste.
Thermography scan: A thermography scan may be performed in conjunction with a blower door test, or as as separate, standalone energy audit diagnostic. A thermographic scanner is typically a camera or video camera that can make the infrared spectrum visible to the human eye. Using this information, an energy inspector can visibly inspect the surface temperature of various components of the home.
Thermography is typically used indoors to measure the coverage and effectiveness of insulation. For instance, if a thermography reveals that one particular spot on an exterior-facing wall has relatively cooler temperature spot, it's likely that that area has less than adequate or missing insulation. Based on this evidence, an energy inspector may recommend adding new, more temperature resistant insulation to that area to improve the home's energy efficiency.
The DOE's Energy Savers program recommends that homeowners prepare for a thermographic scan by helping ensure accurate readings. Moving furniture away from walls and removing drapes from windows can help ensure that temperature variations are correctly attributed to the home's insulation or exterior envelope and not other conditions. Further, the DOE states that to get the best results from a thermographic scan, homeowners in the northern U.S. should have them performed during colder winter months and southern U.S. homeowners should have them performed in warmer months when the AC is typically on.