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How to Prepare for a Blower Door Test

Pretest Preparation

Before conducting the blower door test, we need to put the house in its normal heating or cooling configuration.  This includes closing operable openings and preparing combustion appliances.  The building that is to be tested should be prepared in the following ways:

  • The building should be wired with at least one working 20-amp circuit available to power the blower door fan and usually, the accompanying fog testing equipment.

  • The forces created by the blower door fan for this test (up to at least 50 Pascals) are quite powerful and will tear material from walls that is not securely fastened. Sheetrock and rigid foam will hold, Tyvek, poly, and aluminum vapor and air-barrier materials probably will not.

Doors and Windows

  • A doorway must be provided that can be sealed and off limits to usage for the duration of the test. For the blower door test this will be up to one hour, but the fog test and on-the-spot air sealing work this could be a half day or longer.

  • All interior doors must be open.

  • Close all storm and prime windows.

  • Close all exterior doors and attic or crawl space hatches connected to heated spaces. Also close exterior crawl space hatches.

  • Open all interior doors to rooms that are heated.  The object here is to treat the entire house as one heated space.  Because few basements can be completely sealed from the house and usually some heat to the basement is desirable, they are typically included as a heated space.

  • Tape plastic over window air conditioners if they appear to be a source of air leakage into the house and they are normally removed during the winter.  Close the AC fresh air vents.

Combustion Appliance/Exhaust Devices

  • Adjust any combustion appliances so they do not turn on during the test.  This is usually done by turning off power to the heating system and turning the water heater to the “Pilot” setting.  NOTE:  If vented combustion appliances turn on during a depressurization test, it is possible for flames to be sucked out of the combustion air inlet (flame rollout). This is a fire hazard.

  • Be sure that fires in fireplaces and woodstoves are completely out.  Take precautions to prevent ashes from being blown into the house during the test.  In most cases, closing dampers and doors is sufficient, but when they are leaky or absent, it will be necessary to either tape doors shut, clean out the ashes, or cover the ashes with  wet newspaper.

  • Turn off any exhaust fans, vented dryers, air conditioners and HVAC fans.

  • Do not seal combustions flues, dryer vents, or ventilation system exhaust or intake vents that are normally open in the winter.

 For New Construction

If the blower door test is being performed to document construction quality for new houses, it is usually necessary to temporarily seal all intentional openings in the building envelope (such as dryer vents, ventilation system intakes or exhausts, chimneys, furnaces, water heaters, etc.,).  If buildings are being tested in sections, it will be necessary to isolate (air-tight separation) the test area from other sections of the building.


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