A group gathers for the Blower Door Test workshop.
by Courtney Shea, Chair of the Carbon Neutral Task Force
On a beautiful Friday afternoon in February, about 30 folks from Episcopal churches throughout East Tennessee gathered at the Diocesan House to learn about energy efficiency and to see the new solar installation.
Bruce Glanville introduces the workshop to the concept of the building envelope and the various building methods that contribute to inefficiencies.
What is the Building Envelope and Why does it Matter?
Bruce Glanville, an energy efficiency expert, began with the basics:
The outer shell of a structure (like a Parish Hall) that separates the outside (uncontrolled) environment from the inside, controlled environment is called the “building envelope”. Uncontrolled air movement through the building envelope significantly impacts a building’s comfort and its utility costs. When heated or cooled air escapes through leaks, the building’s heating, ventilation, and air conditioning (HVAC) systems must run longer to maintain the thermostat setting, leading to substantial energy waste. Air infiltration and exfiltration can account for up to 30% to 70% of a building’s heating and cooling energy loss. The goal is to have the air in the building exchanged 3 times per hour (3 ACH).
Air leakage directly contributes to uneven temperatures and discomfort within the building, creating noticeable cold spots or drafts near windows, doors, and floors. Air moving through wall and ceiling cavities also carries water vapor, which can condense on cooler surfaces inside the structure. This accumulation of moisture increases the risk of mold growth, mildew, and structural decay, compromising the durability of the building materials.
Controlling airflow manages indoor air quality and health. Unsealed openings allow unfiltered outdoor contaminants, such as dust, pollen, and vehicle exhaust fumes, to enter the building. Establishing a tight air barrier in our parish buildings reduces energy costs, makes our building temperatures more constant, and gives us better control over the air we breathe.
What are the components of an efficient Building Envelope?
Bruce reviewed 4 aspects of building construction and maintenance:
Bruce Glanville sets up the blower door test equipment.
- Airtight and Insulated: Insulation should be continuous and contiguous, with no thermal breaks. Look where wires and pipes pass through insulated areas; there are often gaps.
- Well-made, well-installed windows and doors: Air leaks and poor drainage are common problems when walls are cut and windows or doors are installed. Poor installation allows moisture penetration. It is important for the building’s integrity that water drains away from it.
- HVAC (heating, ventilation, air conditioning): HVAC requires air delivery and air return from each room in a building. It must be right-sized and match the load on the building: too big; problems such as condensation in the duct system can arise; too small: rooms are not comfortable.
- Air Quality Control: If you make a building tight, you can then control air quality.
Why have a Blower Door Test?
The blower door system consists of three main components: an adjustable frame and flexible panel that seals an exterior door, a variable-speed fan mounted in the panel, and a digital pressure gauge called a manometer. The technician mounts the fan assembly in the exterior doorway and connects the manometer, which measures the pressure differential between the inside and outside air. The fan is typically operated to pull air out of the building, a process called depressurization, which simulates a high-wind condition and forces outside air to rush in through every available leak path. The standard test pressure differential used for residential testing is 50 Pascals (Pa), equivalent to a steady 20-mile-per-hour wind blowing against the home.
Once the 50 Pa pressure is maintained, the manometer registers the exact volume of air the fan must move to maintain that pressure. While the fan is running, the technician may use diagnostic tools such as a smoke pencil or an infrared thermal imaging camera to locate air leakage sites. The smoke pencil releases a harmless stream of smoke that is visibly drawn into cracks, while the thermal camera identifies temperature differences caused by outside air entering the wall assembly.
Bruce Glanville shows Bro. Andrew how a thermal camera can show variances in temperature around doors, windows, light fixtures, and even wall studs.
Using the Blower Test Results
The blower door test generates two primary metrics that allow for a meaningful evaluation of the building’s airtightness. The first is CFM50, which stands for Cubic Feet per Minute at 50 Pascals. This number represents the raw volume of air escaping from the building per minute while the fan maintains a 50 Pa pressure differential. CFM50 is a straightforward measure of total leakage and is useful for tracking the effectiveness of air sealing efforts within a single building.
The second metric is ACH50, or Air Changes per Hour at 50 Pascals. This value is calculated by normalizing the CFM50 reading to the house’s total conditioned volume. ACH50 indicates the number of times the entire volume of air inside the building is exchanged with outdoor air per hour under test conditions. Because it accounts for building size, ACH50 is the standard metric for comparing the relative leakiness of different buildings.
The fan speed can be lowered, and infrared camera or smoke pencil can be used to pinpoint where leaks are occurring.
What happens after the Blower Door Test?
Blower door test results provide a clear roadmap for targeted air sealing efforts focused on creating a continuous air barrier. Common leakage pathways include penetrations by plumbing, electrical wiring, and ductwork that pass through walls, floors, or ceilings. Other significant air leaks are frequently found at the rim joist in the basement, around attic hatches, and behind electrical outlet and switch plates on exterior walls. If weatherization efforts are made, a subsequent blower test can quantify the results and help determine whether more weatherization is needed.
Thanks to Bruce Glanville of Energy Home Basics for the great demonstration. 865-310-1601.
From Bro. Andrew
Updates Specific to the Diocesan House
The results of the blower door test indicated that the diocesan house was experiencing an ACH50 rate of 59, one of the highest that Bruce had calculated on a facility. While any facility can cite a number of sources for the cause of leakage, Bruce was able to quickly identify the insulation in the building as the main culprit of the high ACH50 rate. We contracted with Koala Insulation to remove the old insulation and to install open cell insulation in the attic. Further smaller weatherization improvements are scheduled for the building.
Carbon Neutrality in East Tennessee
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