HERS Blower Door Test

A blower door test provides an accurate way to measure air leakage in a home. Before a final HERS Rating can be established, a blower door test must be given by a trained technician. To perform the test, an exterior door is removed from the home and replaced with a modular hard panel or fabric called a blower door. This new door system, tightly sealed within the door jamb, contains a calibrated, variable speed fan. From this central location, the fan draws air out of the house. This creates a vacuum within the house and causes air from outside to be drawn in wherever possible to replace the expelled air.
Testing begins once the home reaches a certain pressure level (50 Pascals). Using an instrument called an airflow manometer, the technician can now accurately measure how quickly new air is entering the home by measuring the rate at which air moves through the fan while maintaining a constant level of pressure. Simply put, a tight house will require less air flow through the fan to maintain the desired pressure. However, a drafty house will pass more air through the fan.

While the blower door is in operation, you are able to walk through the house and feel the areas that the air is coming in. Commonly drafty areas include sills, corners, around windows, exterior wall fireplaces, plumbing penetrations, eave connections and around electrical fixtures. These are areas which present the greatest challenge when creating a tight home. If the blower door test is done prior to drywall installation, any leaky areas can be addressed before it becomes more difficult to do so.

Blower door results are generally summarized in terms of “air changes per hour.” This metric describes how much of the air in your home will be replaced by air from outside during a 60-minute blower door testing period. An average home built using reasonable air sealing methods would have approximately seven compete air changes per hour. However a home which is built to Energy Star standards will see a blower door test result more in the range of three to five air changes per hour. This can make a significant difference in the amount of energy needed to heat and cool your home.

Before any testing can be done, all openings within the home must be closed or sealed. This includes closing windows, vents and dampers and also plugging drains.