As ATTMA certified blower door testers, training providers and official suppliers of TEC blower door systems, we recommend ‘Air Leakage Test’ as a diagnostic tool to find air leakages that make your building inefficient and are often the cause of moisture-related problems.
Air Leakage Leads to Building Durability Problems
In an air-conditioned space, it is important to limit the ‘Air Leakage’ that negatively impacts comfort, indoor air quality, and energy use in buildings. In addition to carrying heat, air leakage often carries moisture with it, which means that air leaks can lead to a variety of building durability problems.
Examples of air leakage that leads to durability problems include growing mold on roof or wall sheathing due to outward air leakage in cold climates, or condensation on cold ducts or pipes due to inward air leakage in hot-humid climates. In addition, indoor humidity problems are more prominent in Middle East and air leaks are part of them.
This article is about the devices that measure air leakage (such as blower doors and duct blasters), differential pressures, and airflow.
Air Leakage Testing – Blower Doors and Duct Blasters
A blower door (Minneapolis Blower Door) is a calibrated fan used to measure air leakage in buildings; it is typically installed in a fabric shroud mounted in a doorway (Figure 1). The fan is used to depressurize the building to a known test pressure (typically 50 Pascals), and the airflow (cubic feet per minute or CFM) required to reach that pressure is a measurement of the building’s total air leakage (reported as “CFM at 50 Pascals” or “CFM 50”). Blower doors are used for both houses and large commercial buildings (although more fans are needed for the latter).
Duct testing equipment (for example, Duct Blaster) is used in a similar manner to test duct airtightness. The calibrated fan is connected to a ductwork system, the intentional holes in the system (i.e., registers and grilles) are sealed, and the airflow required to reach a test pressure provides a measurement of leakiness.
Incidentally, Duct Blasters are useful for more than ductwork testing. They can also be used to test airtightness of small buildings (such as the cottage in Figure 1), very airtight buildings, or individual dwelling units in multifamily buildings. Figure 2: Testing a house with a blower door.
Differential Air Pressure – Manometers
Air pressures define which way the air moves, and how quickly. Therefore, measuring air pressures during normal building operation can also provide clues to problem conditions. For instance, in southern climates, “buildings that suck” can lead to huge moisture problems from pulling in hot, humid outdoor air.
It’s also useful to have a bit more of an intuitive understanding of the pressure measurement of Pascals/Pa that we use. It is a very small unit—one Pascal is about the weight of a fly on the area of a penny. Also, 1 psi is 6895 Pa. Correctly-operating houses normally operate in the 3-5 Pa range, the blower door and duct blaster tests are run at 50 Pa and 25 Pa respectively, and when buildings are pressurized to exclude contaminants, 10-12 Pa is a typical range.
When we deal with commercial building facility managers and ask them whether their building is running at a positive or negative pressure, they sometimes respond, “they added up the airflows and it should be positive”. Our response always been: let’s measure it directly to figure it out—and plenty of times, adding up the airflows gives the wrong answer. Indoor-outdoor pressure measurements are simple if you can find an operable window or doorway.
These ΔP measurements are also important for residential work—for instance, if they installed an oversized kitchen range hood in a custom house without a makeup air system, we can measure the net effect. Also, very airtight construction with unbalanced fans (e.g., exhaust-only ventilation) can cause problems. Figure 3 and Figure 4 show measurements of indoor-outdoor ΔP at a door or window.
But there are times when a one-time measurement isn’t enough to fully understand what is going on. For instance, on a windy day, it can be next to impossible to tease out the effect of operating fans on house pressures. Also, it can be useful to get a log of operating many mechanical systems (kitchen exhaust, bath exhaust, dryer) in various combinations to determine their effect. In those cases, you can connect Energy Conservatory manometers (pressure meters) to a computer (Figure 5) and use free TECLOG software to graph the pressures in real time, and to observe the effect of changes visually (Figure 6). This creates a computer file that you can refer to and run calculations on later.
Air Flow Indicators – Smoke Pencil, Air Velocity Meter
In addition to putting a number on pressure differences, it’s often useful to demonstrate where air leaks are, and which way airflow is going. The typical go-to solution is a smoke generator or a smoke pencil (Figure 7).
To get more precise, wind or air velocity meters can measure these flows—typically in feet per minute/FPM. You can estimate flows out of HVAC registers by measuring airspeeds and the opening area (called a “traverse”) with these meters.
However, based on our experience, we prefer a hot wire anemometer which has a fine wire that is heated above air temperature, and the rate of heat loss/cooling measures the airspeed. This tool is exceptionally useful because it has an extension probe that lets us “feel” for air leaks out of arm’s reach. A typical use is to depressurize the building and put the probe on suspected air leakage locations.
Figure 8 is the inside of a metal panel building—this panel seam was leaking despite the double-gasket design. Figure 9 shows measurements of air leaks around a windowsill with the trim removed: hot, humid air was getting pulled from the masonry cavity at these openings under the window trim, condensing, and dripping.
Air Flow Measurement Devices – Flow Capture Hood, Exhaust Fan Flow Meter
The equipment that an HVAC technician would use is a flow capture hood (Figure 10)—it can be used for either supplies or returns (up to a limited size).
A useful tool for exhaust fans is a “flow box” (Energy Conservatory Exhaust Fan Flow Meter, Figure 11) It’s a box with a variable opening and measuring the pressure inside the box provides the exhaust flow. It is light, quick, reliable, and works well. Lastly, if you’re looking at exhausts, the “toilet paper test”—despite its simplicity—gives some useful information. If the toilet paper sticks to the fan face, you’re probably getting a decent airflow.