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Question 1Air leakage and duct leakage testing fundamentals

In duct leakage testing, what does the term 'leakage class' describe?

  1. The maximum air velocity permitted inside the duct
  2. The allowable leakage rate normalized to duct surface area and test pressure Correct answer.
  3. The physical thickness rating of the duct sealant applied
  4. The number of access doors installed on a duct run

Explanation

Leakage class expresses allowable leakage as a rate per unit of duct surface area at a specified reference pressure, so it scales with ductwork size rather than being a fixed absolute value. It is a normalized performance rating, not a material or velocity specification.

Question 2Air leakage and duct leakage testing fundamentals

Which quantity is measured directly by a duct leakage tester during a pressurization test?

  1. The airflow required to hold a specified test pressure Correct answer.
  2. The temperature rise across the heating element
  3. The velocity pressure at the supply diffuser
  4. The static pressure drop across the air handler coil

Explanation

A duct leakage test pressurizes the duct system and measures the airflow needed to maintain the target pressure; that airflow is the leakage. Pressure drop, temperature rise, and diffuser velocity are separate system performance measurements.

Question 3Air leakage and duct leakage testing fundamentals

Why must a duct leakage test be conducted with all registers and grilles temporarily sealed?

  1. To allow the duct insulation to dry during the test
  2. To prevent leakage air from escaping through the intended openings Correct answer.
  3. To increase the internal test pressure beyond the fan capacity
  4. To reduce the noise level produced by the test fan

Explanation

Open registers would let the test air escape at the intended delivery points, so the measured airflow would not represent leakage through the duct envelope. Sealing the openings isolates the ductwork as the only leakage path.

Question 4Air leakage and duct leakage testing fundamentals

What is the primary purpose of a building envelope air leakage test using a blower door?

  1. To verify the refrigerant charge in the outdoor condensing unit
  2. To quantify the total air exchange rate through the envelope at a reference pressure Correct answer.
  3. To measure the combustion efficiency of the furnace
  4. To confirm the duct static pressure at the supply plenum

Explanation

A blower door test measures the airflow needed to hold a pressure difference across the envelope, yielding an envelope leakage rate at a reference pressure such as 50 Pa. Refrigerant charge, combustion efficiency, and duct static pressure are separate diagnostics.

Question 5Air leakage and duct leakage testing fundamentals

A duct system is tested at 25 Pa and the measured leakage is 40 L/s. What does this value most directly represent?

  1. The design supply airflow of the air handler
  2. The infiltration rate of the building envelope
  3. The total return airflow at the grille
  4. The airflow needed to maintain 25 Pa inside the sealed duct system Correct answer.

Explanation

The measured airflow is the amount the test fan must supply to hold the specified pressure in the sealed ductwork, which equals the duct leakage at that pressure. It is not a design airflow, grille airflow, or envelope infiltration value.

Question 6Air leakage and duct leakage testing fundamentals

What does a duct leakage test pressure of 25 Pa correspond to in approximate water column units?

  1. About 10 in. w.c.
  2. About 0.1 in. w.c. Correct answer.
  3. About 0.01 in. w.c.
  4. About 1.0 in. w.c.

Explanation

One inch of water column is roughly 249 Pa, so 25 Pa is approximately 0.1 in. w.c. This conversion is useful when comparing metric and imperial test reports.

Question 7Air leakage and duct leakage testing fundamentals

Which instrument is typically used to measure the small pressure differences involved in duct and envelope leakage testing?

  1. A digital manometer Correct answer.
  2. A refrigerant gauge manifold
  3. An infrared thermometer
  4. A clamp-on ammeter

Explanation

Digital manometers resolve the very small pressure differences, often a few pascals, that leakage testing requires. Ammeters, thermometers, and refrigerant gauges measure electrical current, temperature, and refrigerant pressure respectively.

Question 8Air leakage and duct leakage testing fundamentals

Why is it important to record the outdoor temperature and barometric pressure during a leakage test?

  1. Because air density changes affect the relationship between measured airflow and leakage Correct answer.
  2. Because the manometer requires a temperature correction for voltage
  3. Because duct sealant cure time depends on barometric pressure
  4. Because the test fan motor speed is set by the outdoor temperature

Explanation

Air density varies with temperature and barometric pressure, which affects how a measured fan airflow corresponds to a standardized leakage value. Recording these conditions supports correction and comparison between tests.

Question 9Air leakage and duct leakage testing fundamentals

A duct leakage test is run at 25 Pa but the specification requires reporting at 50 Pa. If leakage varies with the square root of pressure, what is the approximate leakage at 50 Pa when 30 L/s was measured at 25 Pa?

  1. About 42 L/s Correct answer.
  2. About 15 L/s
  3. About 60 L/s
  4. About 30 L/s

Explanation

Leakage scales approximately with the square root of pressure, so the factor is the square root of 2, about 1.41. Multiplying 30 L/s by 1.41 gives roughly 42 L/s.

Question 10Air leakage and duct leakage testing fundamentals

During a duct leakage test, the measured airflow will not stabilize and drifts upward. Which condition most likely explains this?

  1. The manometer battery is fully charged
  2. The duct insulation is newly installed
  3. A register seal is loosening under pressure Correct answer.
  4. The test fan is operating below its rated speed

Explanation

A seal that creeps or loosens under test pressure opens an additional leakage path, so the fan must deliver more air to hold the target pressure. Stable, sealed openings are essential for a valid measurement.

Question 11Air leakage and duct leakage testing fundamentals

What is the purpose of establishing a baseline or 'zero' reading on the manometer before a duct leakage test?

  1. To set the fan to its maximum output
  2. To determine the duct leakage class automatically
  3. To account for ambient pressure offsets so the measured test pressure is accurate Correct answer.
  4. To calibrate the duct surface area input

Explanation

Zeroing the manometer removes any offset caused by ambient conditions or instrument drift, ensuring the displayed pressure reflects the actual test pressure. It does not set fan output or compute leakage class.

Question 12Air leakage and duct leakage testing fundamentals

A tester measures duct leakage of 60 L/s at 25 Pa on a system with 40 m2 of duct surface area. What is the leakage rate per unit area?

  1. 24 L/s per m2
  2. 1.5 L/s per m2 Correct answer.
  3. 2.4 L/s per m2
  4. 0.67 L/s per m2

Explanation

Dividing the measured leakage by the duct surface area gives 60 divided by 40, which equals 1.5 L/s per m2. Normalizing by area allows comparison between systems of different sizes.

Question 13Air leakage and duct leakage testing fundamentals

Why is it recommended to test duct leakage before the ductwork is concealed behind finished surfaces?

  1. So that leaks found can be accessed and sealed economically Correct answer.
  2. So that the test fan can be powered from the finished circuit
  3. So that the duct insulation can be omitted during testing
  4. So that the building envelope test can be skipped

Explanation

Testing while ducts are still accessible allows any discovered leaks to be located and repaired without demolition. Concealed ductwork makes remediation costly and may leave defects undiscovered.

Question 14Air leakage and duct leakage testing fundamentals

In a blower door test, what does a result expressed in air changes per hour at 50 Pa (ACH50) represent?

  1. The duct leakage airflow normalized to duct surface area
  2. The supply fan airflow normalized to floor area
  3. The envelope leakage airflow normalized to building volume Correct answer.
  4. The combustion air requirement normalized to burner input

Explanation

ACH50 divides the envelope leakage airflow at 50 Pa by the building volume and expresses it per hour, allowing comparison of airtightness between buildings of different sizes. It is an envelope metric, not a duct or equipment metric.

Question 15Air leakage and duct leakage testing fundamentals

A duct leakage test report states leakage of 45 L/s at 25 Pa. A second identical system tests at 90 L/s at 25 Pa. What does the comparison most likely indicate?

  1. The second system was tested at half the pressure
  2. The second system has roughly twice the leakage area of the first Correct answer.
  3. The second system has twice the duct surface area
  4. The second system has a higher design airflow

Explanation

At the same test pressure, leakage airflow is proportional to effective leakage area, so doubling the measured flow indicates roughly double the leakage area if the systems are otherwise identical. Duct surface area and design airflow do not by themselves change the measured leakage at a fixed pressure.

Question 16Air leakage and duct leakage testing fundamentals

Which factor most affects the repeatability of a duct leakage measurement between two tests on the same system?

  1. The brand of the duct sealant used
  2. Consistency of sealing and stabilization of test pressure Correct answer.
  3. The color of the duct insulation jacket
  4. The number of supply diffusers in the space

Explanation

Repeatable results depend on sealing all openings the same way and allowing pressure and flow to stabilize before reading. Cosmetic or brand factors and diffuser counts do not determine measurement repeatability.

Question 17Air leakage and duct leakage testing fundamentals

What does a duct leakage test at a pressure lower than the specified test pressure generally produce?

  1. An understated leakage value that must be corrected to the reference pressure Correct answer.
  2. An overstated leakage value requiring no correction
  3. A leakage value that cannot be compared to any standard
  4. An identical leakage value regardless of pressure

Explanation

Because leakage rises with pressure, testing below the specified pressure yields a lower measured flow that must be corrected to the reference pressure for comparison. Reporting the uncorrected value would understate leakage.

Question 18Air leakage and duct leakage testing fundamentals

Which of the following best describes the difference between duct leakage and envelope air leakage?

  1. Duct leakage occurs only in heating mode, while envelope leakage occurs only in cooling mode
  2. Duct leakage is confined to the duct system, while envelope leakage crosses the building shell Correct answer.
  3. Duct leakage is measured in pascals, while envelope leakage is measured in watts
  4. Duct leakage affects only return air, while envelope leakage affects only supply air

Explanation

Duct leakage is air escaping or entering the ductwork itself, whereas envelope leakage is air moving through the building shell. They are distinct boundaries tested with different setups, though both use pressure and airflow measurement.

Question 19Air leakage and duct leakage testing fundamentals

A technician tests a duct system and finds the measured airflow drops steadily even though the fan setting is unchanged. What is the most likely cause?

  1. The duct surface area was entered incorrectly
  2. The manometer is reading in the wrong units
  3. A duct opening is being progressively blocked or a damper is closing Correct answer.
  4. The leakage class was set too high

Explanation

A steadily falling airflow at a fixed fan setting suggests the leakage path is shrinking, such as a damper drifting closed or an opening becoming obstructed. Unit selection, area entry, and class settings affect interpretation but not the physical airflow trend.

Question 20Air leakage and duct leakage testing fundamentals

Why should the test fan and flow measurement device be sized appropriately for the expected leakage of the duct system?

  1. So the test can be completed without sealing the registers
  2. So the duct system is pressurized above its design rating
  3. So the leakage class can be estimated without measurement
  4. So the measurement falls within the accurate range of the flow device Correct answer.

Explanation

Flow measurement devices are accurate only within a specified range, so the fan and meter must match the expected leakage to keep readings in that range. Oversizing or undersizing can push the reading outside reliable accuracy.

Question 21Air leakage and duct leakage testing fundamentals

A duct system with 80 m2 of surface area must meet a normalized leakage limit of 1.0 L/s per m2 at the test pressure. What is the maximum allowable measured leakage?

  1. 1.0 L/s
  2. 8 L/s
  3. 800 L/s
  4. 80 L/s Correct answer.

Explanation

Multiplying the allowable rate per unit area by the duct surface area gives 1.0 times 80, or 80 L/s. This is the total leakage the system may exhibit at the specified test pressure.

Question 22Air leakage and duct leakage testing fundamentals

Two duct systems have the same measured leakage at 25 Pa, but system A has twice the surface area of system B. How do their normalized leakage rates compare?

  1. Both systems have equal leakage per unit area
  2. System A has twice the leakage per unit area of system B
  3. System A has four times the leakage per unit area of system B
  4. System A has half the leakage per unit area of system B Correct answer.

Explanation

Normalized leakage divides measured leakage by surface area, so doubling the area while holding leakage constant halves the per-area rate. System A therefore has half the normalized leakage of system B.

Question 23Air leakage and duct leakage testing fundamentals

A tester measures 50 L/s at 25 Pa and needs to report leakage at 50 Pa using a square-root pressure relationship. Which calculation is correct?

  1. 50 multiplied by the square root of 2 Correct answer.
  2. 50 divided by the square root of 2
  3. 50 multiplied by 2
  4. 50 multiplied by the square of 2

Explanation

With leakage proportional to the square root of pressure, the correction factor is the square root of the pressure ratio, here the square root of 2. Multiplying the measured flow by that factor gives the 50 Pa estimate.

Question 24Air leakage and duct leakage testing fundamentals

A duct leakage test yields a stable reading, but a smoke test at the same pressure shows leakage at a joint that was not included in the sealed test boundary. What does this most likely indicate?

  1. The manometer is out of calibration and all readings are invalid
  2. The smoke test pressure exceeded the duct rating
  3. The test boundary did not enclose all intended ductwork, so the measurement is incomplete Correct answer.
  4. The leakage class was calculated incorrectly

Explanation

A stable reading only validates the tested boundary; leakage found outside that boundary means the test did not cover all intended ductwork. The boundary must be corrected and the test repeated to represent the full system.

Question 25Air leakage and duct leakage testing fundamentals

A building envelope test shows a high ACH50, but the duct leakage test on the same home shows low duct leakage. What is the most reasonable interpretation?

  1. The duct system must be leaky despite the low reading
  2. The envelope itself is leaky while the duct system is relatively tight Correct answer.
  3. The envelope test result is always invalid when ducts are tight
  4. The two tests measure the same leakage path and should agree exactly

Explanation

Envelope and duct tests evaluate different boundaries, so a leaky shell and a tight duct system can coexist. The results are not contradictory because each measures a separate leakage path.

Question 26Air leakage and duct leakage testing fundamentals

In duct leakage testing, what does the term "leakage class" typically express?

  1. The pressure rating of the duct material at which it begins to deform
  2. The number of access doors and joints installed per unit length of duct
  3. The allowable leakage rate normalized to duct surface area at a specified test pressure Correct answer.
  4. The maximum air velocity permitted inside the duct under normal operation

Explanation

Leakage class is a standardized way to state how much leakage a duct system may have per unit of surface area at a defined reference pressure. It lets systems of different sizes be compared fairly and is the basis for many specifications and standards.

Question 27Air leakage and duct leakage testing fundamentals

Which condition is essential before starting a duct leakage test on a newly installed system?

  1. All registers and terminal devices must be fully open and operating
  2. The air handler must be running at its design airflow
  3. All intended openings must be sealed and the system isolated Correct answer.
  4. The duct insulation must be fully dry and dust-free

Explanation

A leakage test measures air escaping through unintended paths, so every intended opening must be temporarily sealed and the test section isolated from the rest of the building. Otherwise the test fan also pressurizes other zones and the reading no longer represents duct leakage.

Question 28Air leakage and duct leakage testing fundamentals

A duct leakage test measures 30 L/s at a test pressure of 25 Pa. Roughly how much leakage would be expected at 50 Pa if flow varies with the square root of pressure?

  1. 30 L/s
  2. 60 L/s
  3. 42 L/s Correct answer.
  4. 120 L/s

Explanation

With a square-root relationship, flow scales with the square root of the pressure ratio. Doubling the pressure multiplies leakage by the square root of two, about 1.41, so 30 L/s becomes roughly 42 L/s.

Question 29Air leakage and duct leakage testing fundamentals

Why is it important to use a calibrated, sensitive differential pressure gauge for duct leakage testing?

  1. It compensates automatically for changes in outdoor weather
  2. It allows the test fan to run at a lower speed
  3. It resolves the small pressures involved with acceptable accuracy Correct answer.
  4. It records the total volume of air moved during the test

Explanation

Duct leakage tests are commonly run at reference pressures such as 25 Pa or 50 Pa, which are very small compared with everyday pressure scales. A sensitive, calibrated gauge is needed to read those values accurately and repeatably.

Question 30Air leakage and duct leakage testing fundamentals

A duct system has 60 m2 of surface area and leaks 90 L/s at the test pressure. What is the leakage rate per unit of duct surface area?

  1. 0.015 L/s per m2
  2. 0.67 L/s per m2
  3. 1.5 L/s per m2 Correct answer.
  4. 5.4 L/s per m2

Explanation

Normalized leakage is found by dividing the measured leakage by the duct surface area. Dividing 90 L/s by 60 m2 gives 1.5 L/s per m2, which can then be compared against a specified limit.

Question 31Air leakage and duct leakage testing fundamentals

Which of the following best describes the purpose of a duct leakage test?

  1. To verify that the duct system delivers the design airflow at each register
  2. To measure the sound level produced by the air handler during operation
  3. To quantify air escaping from the duct system through unintended openings Correct answer.
  4. To confirm the duct insulation achieves its rated thermal resistance

Explanation

A leakage test isolates the duct system, pressurizes or depressurizes it, and measures the airflow needed to hold a reference pressure. That airflow represents air escaping through unintended openings such as joint gaps and seam defects.

Question 32Air leakage and duct leakage testing fundamentals

During a duct leakage test, the measured leakage is 40 L/s at 25 Pa. What does this value represent?

  1. The total airflow the duct system carries during normal operation
  2. The volume of the duct system divided by the test duration
  3. The airflow the test fan must supply to maintain 25 Pa in the isolated duct Correct answer.
  4. The pressure drop across the air filter at design flow

Explanation

In a pressurization test, the airflow delivered by the test fan is exactly what escapes through leaks while the reference pressure is held. Therefore the fan flow at 25 Pa is the reported leakage value.

Question 33Air leakage and duct leakage testing fundamentals

A tester reports duct leakage at 25 Pa, but the specification requires the value at 50 Pa. Which step is required to make the report comparable?

  1. Multiply the measured leakage by the pressure ratio
  2. Apply a pressure exponent to extrapolate the leakage to 50 Pa Correct answer.
  3. Add the difference in pressure to the measured leakage
  4. Divide the measured leakage by the test pressure

Explanation

Leakage does not scale linearly with pressure; it follows a power law with an exponent typically near 0.5 to 0.65. Converting a result from one reference pressure to another therefore requires applying that exponent.

Question 34Air leakage and duct leakage testing fundamentals

Why should duct leakage testing be performed before the building is fully finished whenever practical?

  1. Corrective work on accessible ducts is far less costly than after concealment Correct answer.
  2. Instruments read more accurately in empty buildings
  3. Leakage naturally decreases once finishes are installed
  4. Test pressures are lower in unfinished buildings

Explanation

Leaks found while ducts are still exposed can be sealed quickly and cheaply. Once ducts are enclosed behind drywall or ceilings, remediation requires destructive access and is much more expensive.

Question 35Air leakage and duct leakage testing fundamentals

A duct leakage test yields 55 L/s at 25 Pa. The specification limit is 1.0 L/s per m2 and the duct surface area is 50 m2. What is the outcome?

  1. The system fails because 55 L/s exceeds the 50 Pa limit
  2. The system passes because 55 L/s is below 50 m2
  3. The system fails because normalized leakage is 1.1 L/s per m2 Correct answer.
  4. The system passes because leakage limits apply only at 50 Pa

Explanation

Normalized leakage is 55 L/s divided by 50 m2, which equals 1.1 L/s per m2. Since that exceeds the 1.0 L/s per m2 limit, the system does not comply at the stated test pressure.

Question 36Air leakage and duct leakage testing fundamentals

What is the main consequence of testing a duct system at a pressure much lower than the specified reference pressure?

  1. The test fan will be overloaded and may stall
  2. The measured leakage will be higher than the true value at the reference pressure
  3. The duct surface area must be recalculated
  4. The measured leakage will be lower than the value at the reference pressure Correct answer.

Explanation

Because leakage rises with pressure, a test run below the reference pressure captures less leakage than would occur at the specified pressure. Reporting that lower value without correction understates the true leakage.

Question 37Air leakage and duct leakage testing fundamentals

Which practice best reduces uncertainty caused by wind during an envelope or duct leakage test?

  1. Testing only when indoor humidity is at its highest
  2. Increasing the test pressure well above the reference value
  3. Averaging readings over a period and using a zero or baseline check Correct answer.
  4. Running the test fan at maximum speed throughout

Explanation

Wind creates fluctuating pressure differences that add noise to the measurement. Averaging multiple readings and confirming a stable baseline reduces the influence of short-term fluctuations.

Question 38Air leakage and duct leakage testing fundamentals

A duct system shows 20 L/s of leakage at 25 Pa. If the leakage exponent is 0.5, what is the approximate leakage at 100 Pa?

  1. 10 L/s
  2. 20 L/s
  3. 40 L/s Correct answer.
  4. 80 L/s

Explanation

With an exponent of 0.5, leakage scales with the square root of the pressure ratio. Quadrupling the pressure from 25 Pa to 100 Pa multiplies leakage by two, giving about 40 L/s.

Question 39Air leakage and duct leakage testing fundamentals

Why is it important to verify that the test fan and flow meter can resolve the expected leakage before testing?

  1. To guarantee the duct passes the specification limit
  2. To ensure the duct system is fully sealed before the test begins
  3. To eliminate the need for a baseline pressure reading
  4. To avoid operating near the extremes of the instrument's range where accuracy degrades Correct answer.

Explanation

Flow measurement devices are most accurate in the middle of their calibrated range. Oversized equipment may read too close to its minimum, and undersized equipment may be unable to reach the reference pressure, so matching equipment to expected leakage protects accuracy.

Question 40Air leakage and duct leakage testing fundamentals

Which statement correctly distinguishes duct leakage from building envelope leakage?

  1. Duct leakage is measured only in heating mode, while envelope leakage is measured only in cooling mode
  2. Envelope leakage includes duct leakage because ducts are inside the building
  3. Duct leakage is always larger than envelope leakage in the same building
  4. Duct leakage concerns air escaping the duct shell, while envelope leakage concerns air crossing the building shell Correct answer.

Explanation

Duct leakage is air that escapes from the duct system itself, whereas envelope leakage is air moving between indoors and outdoors through the building shell. They are separate pathways and are tested with different setups.

Question 41Air leakage and duct leakage testing fundamentals

A tester measures duct leakage at 25 Pa and also records the corresponding fan pressure. Why is recording the fan pressure useful?

  1. It confirms the duct insulation thickness
  2. It provides the data needed to determine the flow exponent and corrected values Correct answer.
  3. It allows the duct surface area to be calculated
  4. It replaces the need for a calibrated flow meter

Explanation

Measuring leakage at multiple pressures and recording the corresponding fan pressures allows the flow exponent to be derived. That exponent then supports accurate correction to other reference pressures.

Question 42Air leakage and duct leakage testing fundamentals

What is the primary reason for allowing test conditions to stabilize before recording a duct leakage reading?

  1. To give the test fan time to cool down
  2. To let the duct insulation reach outdoor temperature
  3. To allow the building occupants to leave the space
  4. To let transient pressure and flow fluctuations settle so the reading is representative Correct answer.

Explanation

When a test begins, pressures and flows pass through a transient period before reaching equilibrium. Recording only after stabilization ensures the value reflects steady leakage rather than a temporary condition.

Question 43Air leakage and duct leakage testing fundamentals

A duct system leaks 48 L/s at 25 Pa and has 40 m2 of surface area. A second system leaks 72 L/s at 25 Pa and has 90 m2 of surface area. Which system has the higher normalized leakage?

  1. The comparison cannot be made without knowing the duct length
  2. The first system, at 1.2 L/s per m2 Correct answer.
  3. The second system, at 1.8 L/s per m2
  4. Both systems are equal at 1.5 L/s per m2

Explanation

Normalized leakage is 48/40 = 1.2 L/s per m2 for the first system and 72/90 = 0.8 L/s per m2 for the second. The first system therefore has the higher leakage per unit of surface area despite its lower total leakage.

Question 44Air leakage and duct leakage testing fundamentals

Which of the following is a common source of unintended leakage in a newly installed duct system?

  1. Undersized air filter media
  2. Unsealed joints between duct sections and at seams Correct answer.
  3. Excessive insulation thickness
  4. Oversized return grilles

Explanation

Joints, seams, and penetrations are the most common leakage paths because they rely on mechanical fit or sealant rather than continuous material. Proper mastic or tape application at these locations is essential to meeting leakage limits.

Question 45Air leakage and duct leakage testing fundamentals

A tester reports a duct leakage result without stating the reference pressure. Why is this a serious reporting deficiency?

  1. Leakage values are only meaningful in metric units
  2. The reference pressure determines the duct surface area used
  3. Without the reference pressure the leakage value cannot be interpreted or compared Correct answer.
  4. Reporting pressure is optional when the test is done in summer

Explanation

Leakage depends strongly on the pressure at which it is measured, so a flow value without a stated reference pressure has no comparable meaning. Specifications and standards always tie limits to a specific test pressure.

Question 46Air leakage and duct leakage testing fundamentals

What does a leakage exponent close to 0.5 in a duct leakage test suggest about the dominant leak paths?

  1. The leaks are entirely sealed and the test is invalid
  2. The leaks occur only through the air handler cabinet
  3. The leaks are large and turbulent, resembling orifice flow Correct answer.
  4. The leaks behave like a fully open, unchanging orifice

Explanation

An exponent near 0.5 indicates turbulent flow through sharp-edged openings, which is characteristic of typical crack and joint leakage. Higher or lower exponents can indicate different leak geometries or measurement issues.

Question 47Air leakage and duct leakage testing fundamentals

Why might a duct leakage test be conducted at a pressure lower than the operating pressure of the duct system?

  1. Lower pressures reduce the risk of damaging temporary seals and are easier to hold steadily Correct answer.
  2. Lower pressures always produce more accurate results
  3. Operating pressure is irrelevant to leakage
  4. Duct systems never operate above 25 Pa

Explanation

Reference test pressures are chosen as a practical compromise: they are high enough to produce measurable flow but low enough to avoid stressing temporary seals and duct components. Holding a stable low pressure is also easier with portable equipment.

Question 48Air leakage and duct leakage testing fundamentals

A technician seals all registers but forgets to seal the air handler cabinet opening. How does this most likely affect the duct leakage result?

  1. The test pressure cannot be reached at all
  2. The duct surface area must be doubled to compensate
  3. The measured leakage will include cabinet leakage and be higher than the true duct leakage Correct answer.
  4. The measured leakage will be lower than the true duct leakage

Explanation

If the air handler opening remains connected to the test section, air escaping through the cabinet becomes part of the measured flow. The result then overstates leakage attributable to the ductwork alone.

Question 49Air leakage and duct leakage testing fundamentals

Which measurement is most directly needed to convert a measured duct leakage flow into a leakage class per unit area?

  1. The duct surface area of the isolated test section Correct answer.
  2. The outdoor wind speed at the time of testing
  3. The number of occupants in the building
  4. The design airflow of the air handler

Explanation

Leakage class is expressed per unit of duct surface area, so the area of the isolated test section must be measured or calculated. Dividing the measured leakage by that area yields the normalized value.

Question 50Air leakage and duct leakage testing fundamentals

Two tests on the same duct system give 50 L/s and 62 L/s at 25 Pa. Which explanation is most consistent with this spread?

  1. Leakage varies with the cube of pressure
  2. One or both tests had unstable conditions or incomplete sealing Correct answer.
  3. The duct surface area changed between tests
  4. The leakage exponent changed between tests

Explanation

Repeat tests on an unchanged system should agree closely if conditions are stable and sealing is consistent. A spread of roughly 24 percent points to unstable pressure, changing wind, or a seal that shifted between tests.