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NATE_AIRDIST_SERVICE NEC 2023

NATE Air Distribution Service Practice Test 3

This test covers the most common causes of restricted airflow: dirty filters, undersized ductwork, closed or damaged dampers, and a dirty evaporator coil. You will practice identifying these problems from symptoms and static pressure readings.

TOPICS COVERED

NATE Air Distribution Service

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Frequently Asked Questions

Yes — completely free with no signup required. Every question includes a full explanation of the correct answer.

Two: the NATE Core exam plus at least one specialty exam (for example AC Service, Heat Pump Service, or Air Distribution Service). You can take them on the same day or separately.

The Core exam has 50 questions and each installation or service specialty exam has 100 questions. You need 70% on each to pass — 35 of 50 on Core and 70 of 100 on a specialty. Check natex.org for the current format before you book.

NATE certification lasts two years. To renew, you submit 16 hours of continuing education or retake the specialty exam before your certification expires.

No. These are independent practice tests written to match the published NATE exam topics. They are not official NATE exam questions.

Exam Tip: When static pressure is high, work through the airflow path in order: filter, coil, dampers, and duct sizing. Most restrictions fall into one of these categories.

30

Questions

30 min

Time

70%

Pass

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NATE Air Distribution Service Practice Test 3 — Question List

Question 1: Which of these is one of the most common causes of restricted airflow in a residential system?

A dirty air filter
A new thermostat battery
A recently cleaned condenser coil
A properly sized duct system

Question 2: An undersized duct system will most likely cause what?

Decreased velocity and lower static pressure
Increased velocity and higher static pressure for a given CFM
No change in velocity or static pressure
Lower refrigerant charge

Question 3: A closed damper in a branch duct will do what to airflow past that point?

Improve it significantly
Have no measurable effect
Restrict or block it, raising resistance in that branch
Only affect refrigerant subcooling

Question 4: A dirty evaporator coil restricts airflow because it does what?

It changes the refrigerant type
It increases the blower motor's voltage
It causes the thermostat to malfunction
It builds up debris or dust on the coil fins, blocking the air passages between them

Question 5: A technician finds high static pressure. The filter is clean and the coil is clean. What should be checked next?

Dampers and duct sizing/condition, such as a closed damper or crushed flex duct
The refrigerant charge only
The thermostat wiring only
The gas valve pressure only

Question 6: True or False: A crushed section of flexible duct can significantly restrict airflow.

False, flex duct cannot be crushed
True
False, crushed flex duct only affects refrigerant lines
True, but only in commercial systems

Question 7: Why should flexible duct be pulled tight during installation?

To make the duct look neater only
To increase the refrigerant charge
A loose or sagging run increases friction and restricts airflow compared to a straight, taut run
It has no effect on airflow either way

Question 8: A homeowner has not changed their filter in over a year. What is the most likely effect on the system?

No change to the system at all
The refrigerant charge has automatically adjusted to compensate
The thermostat has recalibrated itself
Static pressure has likely risen and CFM has likely dropped over that time

Question 9: A technician measures static pressure across the filter only (before and after) and finds a large pressure drop. What does this indicate?

The filter is restricting airflow and is likely dirty or has too high a resistance for the system
The filter has no effect on the reading
The refrigerant charge is incorrect
The thermostat needs recalibration

Question 10: Which scenario describes a duct system that is undersized for its airflow requirement?

A duct run that is much larger than needed for its airflow
A duct run carrying far more CFM than its diameter was designed to handle efficiently
A duct run with a balancing damper installed
A duct run made of sheet metal instead of flex duct

Question 11: A technician finds a supply register was accidentally closed by a previous occupant. What effect would this have on the rest of the system?

No effect on the system at all
It automatically lowers the equipment's rated static pressure
It can raise static pressure slightly and reduce airflow to that specific room, while shifting more air to other open registers
It always increases total system CFM

Question 12: Which of these would generally NOT cause restricted airflow?

A dirty air filter
A closed damper
A dirty evaporator coil
A recently replaced, clean filter matched to the system's design

Question 13: A homeowner installs a much higher MERV filter than the system was designed for, without any other changes. What is a likely result?

Static pressure may increase because the denser filter media adds more resistance to airflow
Static pressure will always decrease
The refrigerant charge will automatically adjust
There will be no possible effect on airflow

Question 14: A technician finds insulation debris blocking part of a return duct opening in an attic. What is the likely effect?

No effect since it is only insulation
Restricted airflow on the return side, which can reduce total system CFM
Improved airflow because the insulation acts as a filter
A drop in refrigerant charge

Question 15: A system's rated static pressure is 0.50 in. w.c. After replacing a dirty filter, TESP drops from 0.75 in. w.c. to 0.48 in. w.c. What does this show?

The filter change had no meaningful effect
The system is now far below its rated static pressure
The dirty filter was the main source of the excess resistance, and the system is now close to its rated static pressure
The rated static pressure must have changed

Question 16: Which duct problem is most associated with excessive noise as well as restricted airflow?

A duct that is oversized for its airflow
A duct made of sheet metal
A duct with a properly adjusted balancing damper
Ducts sized too small for the required airflow, forcing air to move at high velocity

Question 17: A technician is troubleshooting high static pressure. Which order of checks makes the most sense as a starting approach?

Check the filter first, since it is the easiest and most common restriction to find and fix
Replace the entire duct system before checking anything else
Check the refrigerant charge first, before checking airflow at all
Assume the thermostat is the cause without further checks

Question 18: A partially closed balancing damper in a branch duct was left in the wrong position after a previous service call. What symptom would this most likely cause?

Increased airflow to every room in the house
Reduced airflow to the room served by that branch, with normal airflow elsewhere
A drop in refrigerant charge throughout the system
No effect on airflow anywhere in the system

Question 19: A technician finds both a moderately dirty filter and a partly closed damper on the same system. How would these two restrictions combine?

They would cancel each other out completely
Only the larger of the two restrictions would matter, with no combined effect
Their effects would add together, likely producing higher static pressure and lower CFM than either problem alone
Neither restriction would have any measurable effect

Question 20: True or False: A dirty coil and a dirty filter can both raise static pressure at the same time.

False, only one restriction can exist at a time
False, a dirty coil cannot raise static pressure
False, a dirty filter cannot raise static pressure
True

Question 21: A technician measures normal static pressure across the filter and coil, but static pressure is still high overall. What area should be examined next?

The duct system itself, including dampers, duct sizing, and any kinks or crushed sections
The thermostat display brightness
The color of the supply registers
The homeowner's furniture placement

Question 22: Why is a dirty coil sometimes an overlooked cause of high static pressure?

Because coils never actually get dirty
Because the coil is often hidden inside the air handler cabinet and not as visible as the filter
Because coils have no effect on airflow
Because coils are located outdoors, away from the duct system

Question 23: A homeowner reports weak airflow throughout the entire house, not just one room. Which cause fits this pattern best?

A single balancing damper closed in one bedroom
A disconnected register in one room only
A dirty filter or dirty coil, since these restrict airflow to the whole system rather than one branch
A cosmetic scratch on one supply register

Question 24: Which statement correctly compares a whole-system restriction to a single-branch restriction?

They always produce identical symptoms with no distinguishing pattern
A single-branch restriction always affects the whole house equally
A whole-system restriction only affects one room
A whole-system restriction, like a dirty filter, affects airflow everywhere, while a single-branch restriction, like one closed damper, mainly affects that branch

Question 25: What is a simple maintenance step homeowners can take to prevent one of the most common airflow restrictions?

Replacing or cleaning the air filter on a regular schedule
Closing all supply registers in unused rooms
Increasing the thermostat setpoint
Disconnecting the return duct

Question 26: A technician finds a duct damper that appears to be a manual balancing damper, stuck in a mostly closed position from the factory or installation. What should be done?

Leave it exactly as found, since dampers cannot be adjusted
Adjust the damper to the correct open position needed for proper airflow balance to that branch
Remove the damper and seal the duct closed
Replace the entire duct system immediately

Question 27: A rooftop unit's return duct has a section crushed by foot traffic during a roofing job. What system-wide effect is most likely?

No effect, since return ducts do not affect system airflow
Improved airflow because the crushed section acts as a filter
Reduced return airflow, which can lower total system CFM and raise static pressure
A drop in the equipment's rated static pressure

Question 28: Which pair correctly matches a restriction with its typical location?

Dirty coil — located outdoors on the condenser fan
Closed damper — always located at the thermostat
Dirty filter — located in the refrigerant lineset
Dirty filter — return-air entry point before the blower

Question 29: A technician wants to rule out the coil as a source of restriction without fully disassembling the unit. What is a reasonable first step?

Visually inspect the coil fins for visible dirt or debris buildup, and measure static pressure across the coil if test ports are available
Assume the coil is fine without checking
Replace the entire outdoor unit immediately
Only check the thermostat wiring

Question 30: Overall, what do dirty filters, dirty coils, closed dampers, and undersized ducts all have in common?

They all increase refrigerant charge
They all add resistance to the airflow path, which can raise static pressure and reduce CFM
They all improve airflow when present
They only affect heating mode, never cooling mode

EXAM CARD NATE_AIRDIST_SERVICE

Questions30

Time limit30 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)