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NATE Specialty Air Distribution (AD) Service Exam | Latest
Verified Questions and Detailed Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the NATE
Specialty Air Distribution (AD) Service Exam, which validates a technician's expertise
in installing, servicing, maintaining, and repairing residential and light commercial
HVAC air handling systems up to 30 tons. The assessment is structured around the
Knowledge Areas of Technician Expertise (KATEs): Service (troubleshooting, testing,
adjusting, and repairing duct systems and air handlers) accounts for 40% of the
content, System Components (fans, motors, filters, dampers, etc.) for 25%, Installation
practices (ductwork, insulation, sealing) for 20%, and Applied Knowledge (air
properties, airflow calculations, psychrometrics) for 15%. Core topics include airflow
principles, duct design and sealing, component sizing and installation, and diagnostic
troubleshooting of leaks, obstructions, and noise issues. This nationally recognized
certification is administered by North American Technician Excellence (NATE).
QUESTION 1
What is the primary purpose of a turning vane in a rectangular duct elbow?
A. Reduce duct weight
B. Increase air velocity
C. Minimize pressure loss
D. Amplify sound attenuation
CORRECT ANSWER: C
EXPERT RATIONALE: Turning vanes guide airflow smoothly around the bend, reducing
turbulence and the associated pressure drop. They improve system efficiency without
changing design airflow.
QUESTION 2
A technician measures a static pressure of 0.80 in. w.c. in the supply plenum and -0.30
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in. w.c. in the return plenum. What is the total external static pressure?
A. 0.50 in. w.c.
B. 0.80 in. w.c.
C. 1.10 in. w.c.
D. -0.30 in. w.c.
CORRECT ANSWER: C
EXPERT RATIONALE: Total external static pressure is the sum of the absolute values of
the supply and return static pressures measured across the air handler. 0.80 + 0.30 =
1.10 in. w.c.
QUESTION 3
A residential air handler with a PSC motor is operating with a high total external static
pressure. Which symptom would you most likely observe?
A. Increased airflow CFM
B. Lower motor amp draw
C. Reduced blower RPM
D. Elevated motor temperature and lower airflow
CORRECT ANSWER: D
EXPERT RATIONALE: High static pressure loads the blower wheel, reducing airflow and
causing the PSC motor to operate further from its rated speed, increasing slip and heat.
This results in higher operating temperature and reduced CFM.
QUESTION 4
A customer complains of a whistling noise from a bedroom supply register. The most
likely immediate cause is:
A. Undersized return air grille
B. Excessive face velocity through the register
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C. Return duct leakage in the attic
D. Blower wheel out of balance
CORRECT ANSWER: B
EXPERT RATIONALE: Whistling at a supply register typically indicates air moving too fast
over the louvers or grille bars. High face velocity creates turbulent noise, often due to a
damper being too closed or an undersized register for the airflow.
QUESTION 5
When balancing a residential duct system, which damper should be adjusted first to
establish design airflow in the main trunk?
A. Branch balancing dampers at each room
B. Volume damper at the air handler discharge
C. Fire damper in the main duct
D. Manual balancing damper in the main trunk or take-off collar
CORRECT ANSWER: D
EXPERT RATIONALE: Balancing begins with setting main trunk dampers to proportion
flow to major zones, then fine-tuning branch dampers. A main balancing damper near
the supply plenum sets overall distribution before room-level adjustments.
QUESTION 6
What happens to the airflow through a duct system if the filter becomes excessively
loaded with dirt?
A. Static pressure decreases and airflow increases
B. Total external static pressure decreases
C. Airflow decreases and pressure drop across the filter increases
D. Motor amps always increase dramatically
CORRECT ANSWER: C
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EXPERT RATIONALE: A loaded filter adds resistance, increasing pressure drop across it
and raising total external static pressure, which reduces system airflow. The blower
moves less air against higher resistance.
QUESTION 7
A 10-inch round rigid duct carrying 400 CFM has a velocity of approximately:
A. 500 fpm
B. 733 fpm
C. 900 fpm
D. 1200 fpm
CORRECT ANSWER: B
EXPERT RATIONALE: Area of 10" round = π*(10/12)^2/4 ≈ 0.545 ft². Velocity = CFM /
area = .545 ≈ 734 fpm. Round ducts with 400 CFM at 10" yield velocities in this
range.
QUESTION 8
Which type of fan is most common in residential air handlers due to its low cost and
ability to move air against moderate static pressures?
A. Backward-inclined centrifugal
B. Forward-curved centrifugal
C. Axial propeller
D. Vaneaxial
CORRECT ANSWER: B
EXPERT RATIONALE: Forward-curved (squirrel cage) fans are standard in residential
furnaces and air handlers because they handle typical duct static pressures economically
and compactly. They are less efficient at very high pressures but fit residential needs.
NATE Specialty Air Distribution (AD) Service Exam | Latest
Verified Questions and Detailed Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the NATE
Specialty Air Distribution (AD) Service Exam, which validates a technician's expertise
in installing, servicing, maintaining, and repairing residential and light commercial
HVAC air handling systems up to 30 tons. The assessment is structured around the
Knowledge Areas of Technician Expertise (KATEs): Service (troubleshooting, testing,
adjusting, and repairing duct systems and air handlers) accounts for 40% of the
content, System Components (fans, motors, filters, dampers, etc.) for 25%, Installation
practices (ductwork, insulation, sealing) for 20%, and Applied Knowledge (air
properties, airflow calculations, psychrometrics) for 15%. Core topics include airflow
principles, duct design and sealing, component sizing and installation, and diagnostic
troubleshooting of leaks, obstructions, and noise issues. This nationally recognized
certification is administered by North American Technician Excellence (NATE).
QUESTION 1
What is the primary purpose of a turning vane in a rectangular duct elbow?
A. Reduce duct weight
B. Increase air velocity
C. Minimize pressure loss
D. Amplify sound attenuation
CORRECT ANSWER: C
EXPERT RATIONALE: Turning vanes guide airflow smoothly around the bend, reducing
turbulence and the associated pressure drop. They improve system efficiency without
changing design airflow.
QUESTION 2
A technician measures a static pressure of 0.80 in. w.c. in the supply plenum and -0.30
,2|Page
in. w.c. in the return plenum. What is the total external static pressure?
A. 0.50 in. w.c.
B. 0.80 in. w.c.
C. 1.10 in. w.c.
D. -0.30 in. w.c.
CORRECT ANSWER: C
EXPERT RATIONALE: Total external static pressure is the sum of the absolute values of
the supply and return static pressures measured across the air handler. 0.80 + 0.30 =
1.10 in. w.c.
QUESTION 3
A residential air handler with a PSC motor is operating with a high total external static
pressure. Which symptom would you most likely observe?
A. Increased airflow CFM
B. Lower motor amp draw
C. Reduced blower RPM
D. Elevated motor temperature and lower airflow
CORRECT ANSWER: D
EXPERT RATIONALE: High static pressure loads the blower wheel, reducing airflow and
causing the PSC motor to operate further from its rated speed, increasing slip and heat.
This results in higher operating temperature and reduced CFM.
QUESTION 4
A customer complains of a whistling noise from a bedroom supply register. The most
likely immediate cause is:
A. Undersized return air grille
B. Excessive face velocity through the register
,3|Page
C. Return duct leakage in the attic
D. Blower wheel out of balance
CORRECT ANSWER: B
EXPERT RATIONALE: Whistling at a supply register typically indicates air moving too fast
over the louvers or grille bars. High face velocity creates turbulent noise, often due to a
damper being too closed or an undersized register for the airflow.
QUESTION 5
When balancing a residential duct system, which damper should be adjusted first to
establish design airflow in the main trunk?
A. Branch balancing dampers at each room
B. Volume damper at the air handler discharge
C. Fire damper in the main duct
D. Manual balancing damper in the main trunk or take-off collar
CORRECT ANSWER: D
EXPERT RATIONALE: Balancing begins with setting main trunk dampers to proportion
flow to major zones, then fine-tuning branch dampers. A main balancing damper near
the supply plenum sets overall distribution before room-level adjustments.
QUESTION 6
What happens to the airflow through a duct system if the filter becomes excessively
loaded with dirt?
A. Static pressure decreases and airflow increases
B. Total external static pressure decreases
C. Airflow decreases and pressure drop across the filter increases
D. Motor amps always increase dramatically
CORRECT ANSWER: C
, 4|Page
EXPERT RATIONALE: A loaded filter adds resistance, increasing pressure drop across it
and raising total external static pressure, which reduces system airflow. The blower
moves less air against higher resistance.
QUESTION 7
A 10-inch round rigid duct carrying 400 CFM has a velocity of approximately:
A. 500 fpm
B. 733 fpm
C. 900 fpm
D. 1200 fpm
CORRECT ANSWER: B
EXPERT RATIONALE: Area of 10" round = π*(10/12)^2/4 ≈ 0.545 ft². Velocity = CFM /
area = .545 ≈ 734 fpm. Round ducts with 400 CFM at 10" yield velocities in this
range.
QUESTION 8
Which type of fan is most common in residential air handlers due to its low cost and
ability to move air against moderate static pressures?
A. Backward-inclined centrifugal
B. Forward-curved centrifugal
C. Axial propeller
D. Vaneaxial
CORRECT ANSWER: B
EXPERT RATIONALE: Forward-curved (squirrel cage) fans are standard in residential
furnaces and air handlers because they handle typical duct static pressures economically
and compactly. They are less efficient at very high pressures but fit residential needs.
