Professional energy audits generally go into great detail. The energy auditor should do a room-by-room examination of the residence, as well as a thorough examination of past utility bills.
Many professional energy audits will include a blower door test. Most will also include a thermographic scan. There's also another type of test—the PFT air infiltration measurement technique—but it is rarely offered.
Blower Door Tests
There are good reasons for establishing the proper building tightness:
- Reducing energy consumption due to air leakage
- Avoiding moisture condensation problems
- Avoiding uncomfortable drafts caused by cold air leaking in from the outdoors
- Making sure that the home's air quality is not too contaminated by indoor air pollution.
A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed cracks and openings. The auditors may use a smoke pencil to detect air leaks. These tests determine the air infiltration rate of a building.
Blower doors consist of a frame and flexible panel that fit in a doorway, a variable-speed fan, a pressure gauge to measure the pressure differences inside and outside the home, and an airflow manometer and hoses for measuring airflow.
There are two types of blower doors: calibrated and uncalibrated. It is important that auditors use a calibrated door. This type of blower door has several gauges that measure the amount of air pulled out of the house by the fan. Uncalibrated blower doors can only locate leaks in homes. They provide no method for determining the overall tightness of a building. The calibrated blower door's data allow the auditor to quantify the amount of air leakage and the effectiveness of any air-sealing job.
Preparing for a Blower Door Test
Take the following steps to prepare your home for a blower door test:
- Close windows and open interior doors
- Turn down the thermostats on heaters and water heaters
- Cover ashes in wood stoves and fireplaces with damp newspapers
- Shut fireplace dampers, fireplace doors, and wood stove air intakes.
Energy auditors may use thermography—or infrared scanning—to detect thermal defects and air leakage in building envelopes.
How They Work
Thermography measures surface temperatures by using infrared video and still cameras. These tools see light that is in the heat spectrum. Images on the video or film record the temperature variations of the building's skin, ranging from white for warm regions to black for cooler areas. The resulting images help the auditor determine whether insulation is needed. They also serve as a quality control tool, to ensure that insulation has been installed correctly.
A thermographic inspection is either an interior or exterior survey. The energy auditor decides which method would give the best results under certain weather conditions. Interior scans are more common, because warm air escaping from a building does not always move through the walls in a straight line. Heat loss detected in one area of the outside wall might originate at some other location on the inside of the wall. Also, it is harder to detect temperature differences on the outside surface of the building during windy weather. Because of this difficulty, interior surveys are generally more accurate because they benefit from reduced air movement.
Thermographic scans are also commonly used with a blower door test running. The blower door helps exaggerate air leaking through defects in the building shell. Such air leaks appear as black streaks in the infrared camera's viewfinder.
Thermography uses specially designed infrared video or still cameras to make images (called thermograms) that show surface heat variations. This technology has a number of applications. Thermograms of electrical systems can detect abnormally hot electrical connections or components. Thermograms of mechanical systems can detect the heat created by excessive friction. Energy auditors use thermography as a tool to help detect heat losses and air leakage in building envelopes.
Infrared scanning allows energy auditors to check the effectiveness of insulation in a building's construction. The resulting thermograms help auditors determine whether a building needs insulation and where in the building it should go. Because wet insulation conducts heat faster than dry insulation, thermographic scans of roofs can often detect roof leaks.
In addition to using thermography during an energy audit, you should have a scan done before purchasing a house; even new houses can have defects in their thermal envelopes. You may wish to include a clause in the contract requiring a thermographic scan of the house. A thermographic scan performed by a certified technician is usually accurate enough to use as documentation in court proceedings.
The energy auditor may use one of several types of infrared sensing devices in an on-site inspection. A spot radiometer (also called a point radiometer) is the simplest. It measures radiation one spot at a time, with a simple meter reading showing the temperature of a given spot. The auditor pans the area with the device and notes the differences in temperature. A thermal line scanner shows radiant temperature viewed along a line. The thermogram shows the line scan superimposed over a picture of the panned area. This process shows temperature variations along the line. The most accurate thermographic inspection device is a thermal imaging camera, which produces a 2-dimensional thermal picture of an area showing heat leakage. Spot radiometers and thermal line scanners do not provide the necessary detail for a complete home energy audit. Infrared film used in a conventional camera is not sensitive enough to detect heat loss.
Preparing for a Thermographic Inspection
To prepare for an interior thermal scan, the homeowner should take steps to ensure an accurate result. This may include moving furniture away from exterior walls and removing drapes. The most accurate thermographic images usually occur when there is a large temperature difference (at least 20°F [14°C]) between inside and outside air temperatures. In northern states, thermographic scans are generally done in the winter. In southern states, however, scans are usually conducted during warm weather with the air conditioner on.
PFT air infiltration measurement technique
The airtightness of a building can be determined by using several methods. The PFT (PerFluorocarbon tracer gas) technique and blower door test both provide information about air leakage and energy loss.
How It Works
A blower door test locates air infiltration by exaggerating the defects in the building shell. However, this type of test only measures air infiltration at the time of the test. It does not take into account changes in atmospheric pressure, weather, wind velocity, or any activities of the occupants that may affect air-infiltration rates over a period of time.
The Brookhaven National Laboratory developed the PFT technique to measure changes over time (a few hours to several months) when determining a building's air-infiltration rate. While this test cannot locate exact points of infiltration, it does reveal long-term infiltration problems.
The PFT technique uses two pencil-size devices. One, the emitter, gives off a small amount of a colorless, odorless, and harmless perfluorocarbon gas. The other, the receiver, absorbs some of that vapor from the average concentration of the gas in the room. That average concentration is proportional to the building tightness—the tighter the building, the higher the concentration.
The emitters and receivers are located according to written instructions provided by Brookhaven. The person performing the ventilation measurement begins by uncapping the receiver. Because the rate at which the emitter releases gas is temperature sensitive, the user needs to provide an average temperature estimate during the procedure for the test to be most accurate. At the end of the test period, the receiver is recapped and sent, along with the temperature readings and room volumes, to the Tracer Technology Center at Brookhaven National Laboratory for analysis, where an expert must analyze the results. The Tracer Technology Center sends the customer a computerized test report that includes the average air infiltration rate.
Emitters are available with six different perfluorocarbon gases, making it possible to conduct simultaneous tests in six different areas or zones of a building. Every zone measured requires one receiver. Zones may be physically distinct areas, such as the basement, first and second floors of a house, or distinct heating zones in a zone-heated building. Using more than one gas makes it possible to determine not only the air infiltration rate for each zone but also the airflow pattern between zones, such as between the basement and the first floor. Determining airflow patterns between zones makes it possible to determine air leakage into and out of each zone.
The PFT technique can also determine the infiltration rates of other gases, such as radon. This is done by placing different emitters in the soil next to the foundation, below the basement floor, and in the house. Calculating the rate of infiltration may help detect a potential radon hazard if you live in an area with large radon concentrations.
In addition, the PFT technique can be used to quantify pollutant source strengths in multizone buildings if the user provides pollutant concentration data in each zone taken at the same time as the PFT measurement. In this way, the user will know which location contains the pollutant source even though pollutant is present in all zones.
Preparing for an Energy Audit
Before the energy auditor visits your house, make a list of any existing problems such as condensation and uncomfortable or drafty rooms. Have copies or a summary of the home's yearly energy bills. (Your utility can get these for you.) Auditors use this information to establish what to look for during the audit. The auditor first examines the outside of the home to determine the size of the house and its features (i.e., wall area, number and size of windows). The auditor then will analyze the residents' behavior:
- Is anyone home during working hours?
- What is the average thermostat setting for summer and winter?
- How many people live here?
- Is every room in use?
Your answers may help uncover some simple ways to reduce your household's energy consumption. Walk through your home with the auditors as they work, and ask questions. They may use equipment to detect sources of energy loss, such as blower doors, infrared cameras, furnace efficiency meters, and surface thermometers.
Selecting an Energy Auditor
There are several places where you can locate professional energy auditing services. Your state or local government energy or weatherization office may help you identify a local company or organization that performs audits. They may also have information on how to do your own audit. Your electric or gas utility may conduct residential energy audits or recommend local auditors. Also check your telephone directory under headings beginning with the word "Energy" for companies that perform residential energy audits. See the Learn More section on the right side of the page (or below if you've printed it out) for more auditor resources.
Before contracting with an energy auditing company, you should take the following steps:
- Get several references, and contact them all. Ask if they were satisfied with the work.
- Call the Better Business Bureau and ask about any complaints against the company.
- Make sure the energy auditor uses a calibrated blower door.
- Make sure they do thermographic inspections or contract another company to conduct one.