Infrared Training Center

Friday, September 10, 2010

Blower Door Inspection for Air Infiltration in a Remodeled Cottage

By Tom Coffey, Infrared Training Center
 ITC Logo TM
A small cottage (700 sq. ft) outside of Knoxville, TN was completely remodeled from January to March 2010. It was an existing cinder block structure with no insulation except ½ inch of airspace between the nailers and the block wall as well as the empty block core. The R value of existing building walls was approximately 2.97. After the remodel an R-value was calculated and determined to be 12.6.

2 x 4 studs were used to build the interior walls the insulated with 4” of backed fiberglass bat insulation. Old windows were removed and new double pane sash type windows installed during the remodel.

The house was depressurized to approximately 50 Pascal and allowed to equalize for 30 minutes. A thermographic scan was performed after the equalization period. Infiltration was found around the sash windows where the top and bottom pieces join in the corners of the windows.
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There was some expected infiltration around the front door which was missing a sweep on the bottom of the door. Also infiltration was found at the attic access.
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All of these small problems are easily correctable and will be done as time permits.

The installation of the blower door took approximately 30-45 minutes. Reaching the right depressurization took another 30 minutes and the IR scan took another 45 minutes. For a house this size, allowing for the small footprint I did not do an air exchange calculation. The purpose of this exercise was to determine if the house remodel and adding insulation was sufficient to keep the house at a comfortable level during East Tennessee summers and winters. It was determined during the remodel process that R-13 insulation in the walls and R-19 insulation in the ceilings would be sufficient for the weather conditions in this area of the country.


  1. Question: does the blower door pressurized to 50 Pa "exacerbate" the infiltration that would normally not be present under "normal" pressure conditions? In other words, would it be more prudent to NOT use a blower door so that "typical" conditions can be tested instead of exagerated ones? Not sure.

  2. Absolutely, an IR scan taken under -50 pa is highly atypical and misleading to a homeowner. We back the fan off to -25 pa for scanning, equivalent to about a 10 mph wind to the exterior. Prior to blower door usage we simply turned on kitchen & bath exhaust fans which was more than adequate with a 30+ delta T.
    Jack, Infrared Energy Analysis

  3. When evaluating the energy performance and conservation of the building and continuity of a building shell the 50 Pa is standard to meet ASTM (E779) standard testing procedure. It is not necessary to meet 50 Pa if you just want to perform building shell evaluation with an IR scan to find areas of air infiltration, moisture in the shell cavities, or poor insulation; if adequate delta T exist and wind conditions are acceptable. The standard is important because you have test results that can be compared to industry standards and that you can quantify the energy conservation improvements that are performed.

    There are methods of determining the duct leakage within a building using the air door that would not be determined qualitative or quantitative with using the existing static pressure difference without the air door.

    Also, it is important to have negative pressure when testing gas appliances as the negative pressure produced by exhaust fans may contribute to flame roll out and cumulating of CO before an air door is employed. If not an air door may create a health or explosion hazard due to the testing. One should be familiar with building Performance Institute (BPI) testing standards to perform these tests.

  4. "Question: does the blower door pressurized to 50 Pa "exacerbate" the infiltration that would normally not be present under "normal" pressure conditions?"

    You shouldn't ever run a blower door at 50 pa when performing an infiltration analysis. You will see all kinds of anomalies that may not be there, under normal conditions, if you do. Run the blower door at 25 pa or under.

  5. I asked this because I never use a blower door in an infiltration study - being that that sort of "false" pressurization simply does not happen in the real world. Homes just do not see that sort of pressure differential - test it sometime if you do not believe me. I use a simple technique that if the temperature differential is at least 18 F and no other environmental factors contribute to the analysis, then the analysis should be fine. Just make sure you make notes in your findings of the conditions during the time of the study. True, heavy winds will exacerbate the issue, especially on certain ends of the home or building. In the end, the blower door is simply not needed.

  6. That depends on the temperature. If you do not have an 18 degree ^T you may need to precondition the house. Granted a blower door running at 50 pa will skew the results. That's why you run it at 25 pa or below.

  7. BPI standards, which are mandatory in a number of states (including NJ where I am) call for -50pa to determine leakage rates and are the basis of calculations to determine air-sealing goals and energy savings calculations.

    The infiltration rate is of course "not natural", but, with correction factors, can be calculated to the natural air change rate of the house. I guess one can argue about the physics and accuracy of the conversion factors, but for now it's the standard.

  8. Yuo are correct about -50pa, but if your just looking to pre-condition the house to check for infiltration you should not run the blower door at -50pa. You will get all kinds of false qaulitative images if you do.