How to Ace a Blower Door Test on the First Try

Ace a Blower Door Test in West MichiganA blower door test is the standardized test of air leakage through the home’s envelope. By closing all of the home’s intentional openings in the envelope (windows, doors, mechanical dampers), and putting the home under positive or negative pressure of 50 Pascals (Pa) with respect to the outdoors, you can reveal the amount and location of all the unintentional leakage through the envelope with reasonable accuracy. A pressure of 50 Pa simulates a 25 mile/hour wind on all surfaces. In general, for homes built in Michigan using the prescriptive or total UA paths, the limit for air leakage is not more than 4.00 ACH50.  The test is conducted using a blower door apparatus and is often referred to as a blower door test.

The sure way to pass a blower door test is to seal any openings, cracks, holes or penetrations that connect to the outside prior to ever installing the insulation, unless spray foam is used, which in addition to being a good insulation, is also an excellent sealer that is impermeable to air movement. Properly installed closed cell foam is airtight, but open cell or poorly installed foam is not.  Batt insulation does not prevent air movement, so it is imperative to use proper sealing techniques before installing batt insulation.

Air sealing measures are outlined in the building code in Table N1102.4.1.1. Pay particular attention to the following when preparing for a blower door test:

  1. Testing shall be performed only after the creation of all penetrations of the building thermal envelope. To ensure best chance of passing test, test needs to be performed as late as possible, when all covers are on electrical boxes and home is trimmed out.
  2. Weatherstrip using closed cell foam, all doors/hatches in conditioned spaces leading to unconditioned spaces (attics and vented crawlspaces).
  3. Seal all penetrations to the outside with caulk or spray foam (conduit, wires, HVAC supply/exhaust, power vented water heater exhaust, air conditioning line, cable TV, dryer vent, gas line, )
  4. Seal top plates in attic (interior and exterior walls).
  5. Seal all spaces between window/door jambs.
  6. Seal rim joist, rigid foam (spray foam or caulk seams) or spray foam.
  7. For recessed lighting, seal with gasket or caulk between the housing and interior wall or ceiling covering.
  8. On slab buildings, make sure there is some type of seal between lower plate and slab.
  9. Caulk or foam between electrical outlet/switch boxes and interior walls.
  10. Caulk or foam between supply/return vents and interior walls, floors and ceilings.
  11. Ensure that flaps on all bathroom fans move freely and are functioning properly.
  12. Ensure that all unconditioned knee walls are sealed.
  13. If you have any hidden rooms, make sure that they are sealed as well. Out of sight, out of mind.

Best of luck passing your blower door test!!


Steve Schuehle

Lakeshore Home Diagnostics