First Step to a High-Performing Home: The Blower Door Test

Our homes are important, dynamic parts of our lives — safe havens, the settings of many treasured moments, and significant financial investments. Our homes function best when we can be confident in their health, safety, comfort, dependability, and efficiency.

Understanding the intricacies of a home system can intimidate some, in part because most aren’t taught exactly how our homes operate. For many, it’s the most significant investment of our lives — and it doesn’t come with a manual.

Homeowner anxiety can also stem from not knowing where to begin. In this series of articles on assessing your home’s energy efficiency, we’ll explore the most common high-performing home improvements, beginning with the blower door test.

The Blower Door Test

I spent much of my childhood in an 100-year-old Victorian home in Massachusetts, and as beautiful as it was, this home was about as leaky as they come. Winters are tough enough in Boston, and I can still remember feeling those cold, December drafts sneaking in through the perimeters of windows and doors and from the basement and attic. After 12 years working in the energy-efficiency field, I now know that these drafts greatly contributed to my childhood asthma and allergies!

To help keep your home healthy, comfortable, and efficient, you first need to understand where improvements are needed. I always recommend starting with an energy assessment by a qualified professional. An energy assessment, or energy audit, is a professional analysis of a home’s energy consumption and energy efficiency.

That brings us to the blower door test — the critical component of every quality energy assessment. As a fundamental tool, the blower door test helps determine the “air tightness” of a home. This test measures the amount of air that leaves and enters a home through its enclosure, or as it’s commonly known in the energy efficiency field, its “envelope.” 

In a blower door test, a professional contractor will de-pressurize your home using a powerful fan temporarily mounted to a door frame. Driving the air out this way will cause outside air to be sucked into your home through any existing gaps in the envelope. As the fan blows air out, your contractor will walk through your home, using incense or smoke to find those leaks and prepare them for sealing (see our next article in the series for more on common leak points and air sealing).

Why does air tightness matter? That comes down to something called the “stack effect,” but you probably know it as, “My first floor freezes in the winter, and my second floor stifles in the summer,” or simply, “Gasp! My energy bills!” Bear with me while I talk a little building science.

Because warm air is less dense than cold air, on a cold day, low-density, high-pressure warm air will rise in your home and escape via whatever gaps exist on higher levels. This creates a vacuum on the lower floors, sucking in colder air through gaps farther down (hello, crawl space). On hot days, the opposite happens; warm air is pulled into your home through gaps, say, in your attic and drives cold air, and your dollars, down and out through gaps on the first floor.

Gaps can wreak havoc on the comfort of your home and your energy bills, but they also impact health.Think about it. Air pulled into the home through gaps in the walls, attics, and crawl spaces is passing through old insulation, bugs, dust and dirt, animal droppings, and more. In polluted or high-pollen areas, the air may not even be that great before it enters the home. I'm not the only person to deal with respiratory issues due to a drafty home. In my work as a professional contractor and a consultant, I’ve seen children and adults beset by allergies and asthma due to the quality of air in their homes. Moreover, numerous studies have linked poor indoor air quality and short- and long-term respiratory illness in the young and the old.

It is very important that blower door tests are performed by accredited professionals. Experienced energy auditors will know how to safely and properly prepare the home for the test, including safely shutting down the appropriate appliances and HVAC systems.

After the Blower Door Test: Air Sealing and Insulation

Once you have your assessment results, you can start making improvements for health, comfort, and savings. Start with tightening your home through air sealing. Air sealing your home will set the stage for later improvements like heating and cooling system upgrades and insulation improvements, which are best done only after the home has been properly sealed.

The second improvement I usually recommend after an assessment is to ensure your home has substantial, properly installed attic or roof insulation. High-quality insulation companies typically provide both air sealing and insulation improvements and should conduct a second blower door test to evaluate their work.

Every homeowner wants their home to be safe, healthy, comfortable, and efficient, and blower door tests conducted during energy assessments are an important first step.