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Blower Door Testing

Proper home construction and attention to air sealing are what makes for a pleasant indoor climate. A blower door test is an important part of the air sealing process used by technology-driven building professionals to measure and correct unintentional air leakage during home construction and remodeling. Homeowners who are interested in energy-efficiency, green home certification, or simply concerned about indoor air quality and comfort, may consider asking their contractor to perform a blower door test. Blower door tests can help prevent many unwanted home problems such as: humidity, mold, allergies, pest intrusion, and high energy bills. If those sounds like things you want to avoid during your next build or remodel, read on the learn about the benefits and process of blower door testing.

The Importance of Good Indoor Air Quality

When stepping into a home, most people can immediately sense the indoor air quality (IAQ) whether they recognize it or not. A drafty home will feel cooler near the walls or have seemingly random cold spots. Some homes feel damp inside or have a musty smell that never goes away. These indicators tell us that the IAQ is poor. Poor IAQ is often caused by an air sealing problem in the envelope of the home.

Builders refer to the outer layers of a home as the “building envelope”. A building envelope consists of the framing, sheathing, weather barrier, siding, and insulation. How well these parts are installed, and how well they seal the home from outdoor air, determines how well the whole house performs and feels. No home is 100% sealed, nor should it be, but less air leakage is generally a good thing. Homes with a tight envelope (in conjunction with air circulation systems) are better for the planet—and your bank account—because heating and cooling systems don’t have to work as hard. They’re also better for your health.

Especially for homeowners with young children, allergies, asthma, or sensitivities, we recommend focusing a good portion of your home building investment on air quality. While shiny finishes are certainly beautiful, the comfort of your home is arguably more important. If you’ve ever spent time in a damp or drafty home, you know just how much poor indoor climate can impact how you feel. Additionally, Pacific Northwest summers are becoming increasingly plagued by forest fire smoke. A properly sealed and conditioned home will prevent pollutants, such as smoke, from circulating throughout the house.

For all these reasons and more, a blower door test can ensure your home is going to have a good envelope. A good building envelope is the first step towards good indoor air quality.

What is a Blower Door Test?

A blower door test is an experiment to measure air leakage from a home, with the goal of finding and fixing any weak points within its air barrier. The test is performed by a contractor or licensed energy auditor using special equipment to seal and pressurize (or depressurize) the home. A single door of the home is fitted with a large, calibrated fan that creates a measurable pressure difference between the indoors and outdoors.

Prior to test, all openings that are still being built or already in place, need to be sealed. These include plumbing, venting, exhaust, and chimneys. Combustible appliances like heaters and fireplaces need to be turned off. Unconditioned spaces, like unfinished attics or crawlspaces, need to be fully sealed off from the conditioned space. Lastly, exterior doors and windows need to be closed and locked to ensure a tight seal. An energy auditor or contractor knows what to look for and all the areas that need to be checked prior to the test. Setup usually takes the most time during a blower door test.

When the test is being performed, the fan is hooked up to a computer program that tracks and calculates a variety of metrics, including CFM (cubic feet per minute) and ACH50 (air changes per hour at the pressure of 50pascals). These metrics tell a builder how well the home is sealed and allow them to make real-time air sealing adjustments to improve the level of air leakage.

How is Air Leakage Measured?

The primary metric to watch during a blower door test is ACH50. This metric shows how many times the volume of air within the home changes, every hour, when the outside air is at stable test conditions.

The International Energy Conservation Code (IECC) has lowered air leakage requirements over the years. Once at 7 ACH50 in the early 2000s, the current code (2021) for new home construction requires 3 or 5 ACH50 in most of the United States. Achieving an ACH50 of 3 to 5 is standard, but many modern builders are reaching for even more impressive results. Here in Seattle, when certifying a home through the local Built Green program, we aim for an ACH50 below 3. High performance homes aim to achieve an ACH of 1.0 or below.

Older homes have a considerably higher ACH rating, generally somewhere between 6 and 10. It is possible to section of a home and only test new space. For example, when building a bump-out addition to the back of your home you may want to do a blower door test for only the new space.

When to Preform a Blower Door Test

We most often perform blower door tests on homes that are either being fully remodeled or entirely rebuilt. A blower door test can also be performed on a large addition. Home projects certified through a green building program will require a blower test.

Here in the Pacific Northwest, green building programs include Built Green, LEED, Passive House, the Living Building Challenge and more. Certification is a good investment if you ever plan to sell your home in the future. Many studies show that homebuyers will pay a premium for a home with green certification and demand is only increasing. Even if certification isn’t something you’re interested in, a blower door test is a worthwhile investment for large residential remodeling projects and new home construction.

Blower door tests are most often performed at the end of construction when walls are up, siding is installed, and exterior windows and doors are in. However, there are many benefits to performing a blower door test earlier in the building process. If a blower door test is done prior to insulation, exterior walls are visible. This makes it easier to find and fix the points of air leakage. At early stages, it may be most efficient to use an advanced air sealing system like AeroBarrier. Otherwise, a contractor will walk around the home during the blower door test to feel for spots where air is coming in. Point of air leakage will be fixed on the spot, or marked for later. Sometimes a theatrical smoke machine is used so air leakage is visible, too.

How Air Sealing, Insulation & HVAC Work Together

To recap, a blower door test is a great check for builders and homeowners seeking a tight building envelope. A “tight” home—one that has little air leakage and is well-insulated—is only part of the equation to quality home construction. Air circulation and ventilation through an HVAC system and/or whole house fan is a critical last step to creating a comfortable home.

Without air circulation systems you have created a home with the opposite problem of a leaky one: stagnant air. Stagnant homes do not control moisture or regulate temperature. So just like Goldilocks, the sweet spot in home building lies somewhere in the middle. Seal a home too little and it’s drafty. Seal a home too much and it would lead to air quality issues. Mechanical systems that move and replace air are a key component of the home comfort trifecta.

A home with great air sealing, above-code insulation and effective air circulation will have the best indoor air quality no matter what the weather, air quality, or pollen level is outdoors. A blower door test is a proven tool for home building and remodeling professional to ensure a home has successfully achieved the first step in the home comfort trifecta.

Blower Door Testing Q&A

What is a blower door test?

A blower door test is an experiment to measure air leakage from a home, with the goal of finding and fixing any weak points within its air barrier.

How long does a blower door test take?

Most blower door tests take less than 30 minutes. Preparation of the home and equipment setup/take-down typically takes a few hours. It all depends on the size of the space or home being tested, but the actual test run-time doesn’t take very long.

What is a good blower door test score?

Most home builders are looking to achieve an ACH50 of 3 or below. Current International Building Code (2021) requires 3 or 5 ACH50 in most of the United States, but high performance homes have even stricter standards at or below 1 ACH50.

When is a blower door test required?

Some state and local jurisdictions require a blower door test for new construction and home additions. For high performance home building and certain green building certifications, such as LEED or Passive House, blower door tests are required to meet strict standards. Local governments will often provide expedited permitting and other incentives for high performance, energy-efficient homes, with proof of a blower door test and other criteria.

Written by Model Remodel

Model Remodel is a design-build, remodeling contractor located in Seattle, WA. For over 20 years we’ve been building with purpose, craftsmanship and sustainability in mind. We are proud to continually make the list of top Seattle contractors for our beautiful interior designs and homeowner-focused remodeling process.

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