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NATE_AIRDIST_SERVICE NEC 2023

NATE Air Distribution Service Practice Test 4

This test covers duct materials and basic duct design: sheet metal versus duct board versus flexible duct, friction and velocity concepts, and why proper duct sizing matters for airflow and noise.

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: Remember that smoother interior surfaces (like sheet metal) generally create less friction than flexible duct, especially if the flex duct is not pulled tight.

30

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30 min

Time

70%

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NATE Air Distribution Service Practice Test 4 — Question List

Question 1: Which duct material is rigid, durable, and has a smooth interior that creates less friction?

Sheet metal
Flexible duct
Cardboard duct board
PVC refrigerant tubing

Question 2: What is a key feature of fiberglass duct board?

It is always used for refrigerant lines
It has built-in insulation as part of the duct material itself
It cannot be used indoors
It has the smoothest interior of any duct material

Question 3: Flexible duct ("flex duct") must be installed in what way to avoid excess friction?

Left loose and coiled for flexibility
Buried directly in insulation with no support
Pulled tight and supported, without kinks or crushed sections
Installed with as many sharp bends as possible

Question 4: What happens to air velocity and static pressure when a duct is sized too small for its required airflow?

Velocity and static pressure both decrease
Velocity decreases while static pressure increases
Velocity increases while static pressure decreases
Velocity and static pressure both increase

Question 5: A correctly sized duct system aims to balance which two factors?

Adequate airflow and reasonable noise/pressure loss
Refrigerant charge and subcooling
Thermostat setpoint and humidity level
Gas pressure and combustion efficiency

Question 6: What term describes the pressure loss per 100 feet of duct, used as a general concept in duct design?

Superheat rate
Friction rate
Subcooling rate
Combustion rate

Question 7: True or False: A smooth interior duct surface generally creates less friction than a rough or ridged interior surface.

False, rough surfaces always create less friction
False, surface texture has no effect on friction
True
True, but only in cooling mode

Question 8: Compared to sheet metal, why does flex duct often have higher friction for the same length and airflow?

Flex duct is always installed with more insulation than sheet metal
Flex duct carries refrigerant instead of air
Flex duct is never insulated
Its ridged interior surface creates more turbulence than a smooth sheet metal interior

Question 9: A technician finds a long, sagging run of flex duct in an attic that dips well below its supports. What is the likely airflow effect?

Increased resistance and possibly reduced CFM to the register it feeds
No effect since flex duct is designed to sag
Improved airflow due to the extra duct length
A drop in the system's rated static pressure

Question 10: Which of these is an advantage of sheet metal duct over flex duct?

It is always cheaper to install than flex duct
Its smooth interior offers less resistance to airflow over an equal length
It never needs to be insulated
It automatically balances airflow between rooms

Question 11: A branch duct run needs to make a turn. Which design choice would generally add less resistance?

A sharp 90-degree elbow with no radius
Two sharp 90-degree elbows placed back to back
A gradual, wide-radius turn instead of a sharp 90-degree elbow
A crushed section instead of any fitting

Question 12: True or False: Duct design tables that specify exact friction rates and sizes exist, but exact design calculations go beyond basic troubleshooting concepts.

False, no such tables exist
False, exact duct sizing is never used in the industry
False, friction rate is not a real concept
True

Question 13: What is a practical reason flex duct is popular in residential attics and crawlspaces?

It is easier to route around obstacles like framing and other utilities
It never needs support of any kind
It always has less friction than sheet metal
It cannot be insulated

Question 14: A duct system was designed for 400 CFM in a branch run, but the installer later added a second register to the same branch without upsizing the duct. What is a likely consequence?

No consequence, since duct size does not depend on airflow
The branch may now be undersized for its total airflow, increasing velocity and static pressure
The refrigerant charge will need to be increased
The blower motor type will automatically change from PSC to ECM

Question 15: Which material combination correctly matches a duct type to a defining trait?

Sheet metal — insulation is always built in
Flex duct — has the smoothest possible interior
Fiberglass duct board — insulation is built into the duct material
Sheet metal — cannot be used for supply ducts

Question 16: A technician measures unusually high static pressure and finds several sharp turns and fittings crowded close together near the air handler. How does this layout contribute to the reading?

Fittings never add resistance, only straight duct length matters
This layout has no effect on static pressure
This layout would only affect refrigerant pressure, not air pressure
Multiple sharp fittings close together add up their resistance, contributing to overall system static pressure

Question 17: What is one downside of using a duct that is much larger than needed for its actual airflow?

Air velocity may be too low for good air mixing and distribution in the space, and it costs more material
It always increases static pressure above rated levels
It always causes duct leakage
It has no downsides of any kind

Question 18: Duct board and flex duct are both often pre-insulated. What is the main benefit of this?

It eliminates the need for a blower motor
It helps reduce heat gain or loss through the duct wall as conditioned air travels through it
It increases the MERV rating of the system
It removes the need for a return duct

Question 19: A supply trunk duct splits into two branch ducts of equal size feeding two rooms with very different airflow needs. What potential design problem does this create?

No problem, since equal duct size always means equal comfort
This automatically increases the equipment's rated static pressure
One room may receive too much airflow while the other receives too little, since equal duct size does not guarantee equal delivered airflow matched to each room's needs
This would only be a problem in a zoned system

Question 20: Which of these duct materials is generally considered the most rigid and resistant to being crushed?

Flexible duct
Fiberglass duct board
Neither material is more rigid than the other
Sheet metal

Question 21: A technician needs to run duct through a tight attic space with many obstacles. Which material would likely make installation easiest, as long as it is properly supported?

Flexible duct
Rigid sheet metal only
Refrigerant-grade copper tubing
PVC drain pipe

Question 22: True or False: Using more flex duct length than necessary, even if not kinked, can still add unnecessary friction to a run.

False, duct length has no effect on friction
True
False, only kinks matter, not overall length
True, but only for sheet metal duct

Question 23: A homeowner hears a whistling or rushing noise at a supply register. What duct design issue could explain this?

The refrigerant charge is too high
The thermostat display is malfunctioning
The duct or register may be undersized for the airflow passing through it, causing high velocity noise
The gas valve is stuck open

Question 24: When comparing duct materials for a main trunk line in a new install, which factor would most influence whether sheet metal or duct board is chosen?

The color of the homeowner's walls
The brand of thermostat installed
The refrigerant type used by the equipment
Design preferences around rigidity, cost, and airflow resistance for that specific application

Question 25: What is the main purpose of correct duct sizing in system design?

To deliver the required airflow to each room while keeping noise and pressure loss reasonable
To increase static pressure as much as possible
To reduce the number of registers needed
To eliminate the need for a return duct

Question 26: A technician is asked to add a new branch duct to an existing system to serve a room addition. What should be considered to avoid overloading the existing duct design?

The color of the new ductwork, to match the existing system
Whether the existing trunk duct and equipment have enough spare capacity (CFM and static pressure margin) to support the added branch
The brand of thermostat used in the room addition
The refrigerant charge of the outdoor unit

Question 27: Which statement about duct fittings and static pressure is TRUE?

Fittings never add any resistance to airflow
Only elbows located outdoors add resistance
Each fitting, such as an elbow or transition, adds some resistance to the airflow path
Fittings only affect refrigerant flow, not air flow

Question 28: A technician replacing old ductwork chooses sheet metal for a section running through a mechanical closet with limited space and potential for accidental impact. What is the main reasoning?

Sheet metal is always cheaper in every situation
Sheet metal has more built-in insulation than duct board
Sheet metal eliminates the need for a filter
Sheet metal's rigidity better resists damage from impact or being crushed in a high-traffic space

Question 29: Which best explains why velocity is an important concept in duct design, beyond just static pressure?

High velocity can cause noise and added friction, even before static pressure becomes a problem elsewhere in the system
Velocity has no relationship to noise or friction
Velocity only matters for refrigerant lines, not air ducts
Velocity is only relevant in commercial systems, never residential

Question 30: Overall, why does a technician need to understand duct materials and design basics, even if they did not design the original system?

It is not useful information for a service technician
It helps them recognize installation problems, such as undersized runs or poorly supported flex duct, that could be causing airflow complaints
It only matters for technicians who install new systems, never for service technicians
It replaces the need to measure static pressure or CFM

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)