A blower door is a machine used to measure the airtightness of houses. The test will analyze the pressure differential from outside to inside, with a fan creating negative pressure of 50 pascals inside the building.

50 pascals is used to imitate the pressure of a strong wind.

It can also be used to:

• measure airflow between building zones
• test ductwork airtightness
• help physically locate air leakage sites in the building envelope.
  

In the near future, building code may mandate that blower door tests done on new construction to ensure building standards are met. At present, they are mostly done as either a part of an energy assessment or if a new building is targeting a specific energy standard.

Homeowners will often book an assessment before starting a renovation so they can take advantage of any government incentives for improvements made to their home. The Energy Advisor will perform the blower door test and do a complete walkthrough to locate problem spots around the house.

With any renovation based on increasing the airtightness and insulation levels, the work must include a plan for installing and balancing an HRV to ensure consistent fresh air flow and exhaust of stale air.

This is why it's equally important to get the test done after the renovation as it is before.

There are two main types of fan for blower door testing - calibrated and uncalibrated. For measuring the air tightness of a building, a calibrated fan must be used, as it can be hooked up to gauges and equipment to collect data from the unit. An uncalibrated fan is used for finding leaks.

During the testing process, the following must be done to prepare:

• All windows and exterior doors must be closed during the test
• All interior doors must remain open during the test
• The blower door measures the pressure difference between the exterior and interior of the home
• Shut off heating / air conditioning and gas / oil fired water heating equipment
• Close all fireplace, wood stove and chimney flu openings (dampers)
• Empty ashes from wood burning stoves and fireplaces
• Arrange the test around a time when fewer occupants are home.

The air pressure of 50 Pascals forces air into or out of the home through leakage areas depending on the type of test performed.