How to conduct a blower door test
Once the building is closed up completely, install the blower door in an exterior door opening.
Many buildings waste significant amounts of energy. Energy audits reveal how energy is being used in buildings and identify opportunities for energy and cost savings. An energy audit of a commercial or residential structure can be used to:
- Reduce energy consumption due to air leakage
- Avoid moisture condensation problems
- Identify the source of cold air drafts
- Make sure air quality is not contaminated by indoor air pollution
An important step in an energy audit is to conduct a blower door test.
How to conduct a blower door test
A blower door is a powerful fan that is temporarily mounted into an exterior doorway. It pulls air from the building to lower the air pressure inside. The higher-pressure air outside will then flow in through unsealed cracks and openings, making it possible for the auditors to find air leaks.
A blower door includes a frame and flexible panel, a variable-speed fan, a pressure gauge to measure the pressure differences inside and outside the building, an airflow manometer and hoses for measuring airflow.
Blower doors can be calibrated or uncalibrated. A calibrated door has gauges that measure the amount of air pulled out of the structure by the fan and the effectiveness of any air-sealing work. Uncalibrated blower doors can only locate leaks.
- The frame and shroud are then set into the door jamb and adjusted to create a tight fit.
A blower door test
Step 1
Turn off all appliances and close all windows, doors, chimney flues or other openings to the outside. Pour water into any open floor drains to prevent air from being pulled back through pipes.
Step 2
Once the building is closed up completely, install the blower door in an exterior door opening. Typically, the front door is used. Photo 1 shows the adjustable blower door frame, which is assembled and then covered with a canvas shroud, shown in Photo 2. The frame and shroud are then set into the door jamb and adjusted to create a tight fit. A powerful, variable speed fan is inserted into a round opening at the bottom of the shroud (Photo 3).
A powerful, variable speed fan is inserted into a round opening at the bottom of the shroud.
When the fan is turned on, the manometer will measure the pressure difference between the inside and outside of the building, as well as the volume of air moving through the fan in cubic feet per minute (cfm).
Step 3
Connect the manometer to the fan (Photo 4). When the fan is turned on, the manometer will measure the pressure difference between the inside and outside of the building, as well as the volume of air moving through the fan in cubic feet per minute (cfm). The air volume reading allows you to determine how “tight” the building is. A tighter building will require more air volume passing through the fan to achieve the desired test pressure differential. The typical pressure differential goal used for the test is -50 Pascal. This force created by this pressure differential is roughly equivalent to the force of a 25 mph wind. Sometimes there is enough force to move a ceiling tile or dislodge a poorly installed window pane.
To discover pressure differences between each room and the baseline area where the blower door is set up, a long thin hose is attached to a manometer and the other end of the hose is inserted past the closed door of each room.
Step 4
Turn on the fan and increase the speed until the proper pressure differential between inside and outside is achieved. To discover pressure differences between each room and the baseline area where the blower door is set up, a long thin hose is attached to a manometer and the other end of the hose is inserted past the closed door of each room (Photo 5). By comparing the pressure difference between each room and the baseline area, you can determine if substantial air infiltration is occurring in that room.
Once you have determined and recorded the various pressure differentials in each room, try to pinpoint where the air infiltration is occurring.
Step 5
Once you have determined and recorded the various pressure differentials in each room, try to pinpoint where the air infiltration is occurring. To do this, you can use an Infrared Thermal Imaging Camera (Photo 6). This camera shows temperature variations at any surface at which the camera is pointed and can capture a digital picture of that view. The temperature variations are shown by different colors, and a digital read-out of the actual temperatures being detected shows on the screen.
The usual places to look for infiltration are windows, exterior doors, along the baseboard, along the ceiling, attic doors, rim hoists, top plates, chimneys, ceiling fans, air diffusers and any penetrations through the wall for electrical, such as duplex outlets or other mechanical work.
The Infrared Thermal Imaging Camera will show temperature variations anywhere the camera is pointed. Here, temperature variations are shown by different colors, and a digital read-out of the actual temperatures being detected shows on the screen.
With the information gathered, you will have a good understanding of where additional caulking or insulation should be installed to reduce air infiltration. While some improvements may be costly, others are inexpensive and can easily pay for themselves in energy savings in a short period of time.
The various test data and requirements for blower door tests are not yet fully standardized. Two of the most recognized sources for energy conservation training and certification are BPI (Building Performance Institute), which covers building analysis technical standards and testing practices. They can be reached at www.bpi.org.
A second resource is RESNET, which is primarily concerned with new construction, energy ‘ratings’ and achieving energy rating certifications, such as LEED. They can be reached at resnet.us.
[tip id=”8070″]Before you start
Before conducting a blower door test, it is strongly recommended you conduct a combustion efficiency test for all gas fired appliances. This analysis checks to see how efficiently appliances are working and if flues are adequately expelling excess carbon monoxide. If you find a high level of carbon monoxide is present at one or more of the appliances, it can be an indication the structure is not properly vented and a blower door test should not be conducted until this is corrected.
‒By Bruce Webb, General Contractor
