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NATE_AIRDIST_SERVICE NEC 2023

NATE Air Distribution Service Practice Test 5

This test covers duct leakage and sealing: the difference between supply-side and return-side leaks, why proper sealing materials matter, and how leaky ducts affect comfort and energy use.

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 mastic or foil tape is used to seal ducts, not standard cloth "duct tape," which tends to dry out and fail over time.

30

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30 min

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70%

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NATE Air Distribution Service Practice Test 5 — Question List

Question 1: What happens when a supply duct leaks conditioned air before it reaches a room?

Energy is wasted and the room may not get its full designed airflow
The system automatically compensates with no effect on comfort
Static pressure always drops to zero
The refrigerant charge increases

Question 2: What can happen when a return duct leaks in an attic or crawlspace?

No effect, since return leaks only affect the equipment cabinet
Unconditioned air can be pulled into the system, adding load and sometimes contaminants
The blower motor automatically shuts off
The thermostat recalibrates itself

Question 3: Which material is recommended for sealing duct joints and seams?

Standard cloth duct tape
Electrical tape
Mastic or foil tape
Silicone caulk only

Question 4: Why does standard cloth "duct tape" perform poorly for sealing ducts long-term?

It is too expensive to use on ductwork
It is not manufactured in wide enough rolls
It reacts chemically with sheet metal
Its adhesive tends to dry out and fail over time, letting the seal open back up

Question 5: A technician finds a return duct running through an attic with several unsealed seams. What is the likely consequence, especially in summer?

Hot, dusty attic air is pulled into the return airstream, adding heat load and reducing indoor air quality
The system will automatically increase its rated static pressure
No effect, since return duct leaks only matter in winter
The refrigerant charge will decrease

Question 6: True or False: Supply duct leaks and return duct leaks have identical effects on the system.

True
False
True, but only in cooling mode
False, only supply leaks exist in real systems

Question 7: A homeowner complains their energy bills are high and comfort is uneven room to room. Duct leakage in the attic is suspected. What would be a reasonable next step?

Replace the thermostat immediately
Increase the refrigerant charge
Inspect and pressure-test the duct system to identify and locate leaks before sealing them
Close all supply registers in every room

Question 8: A smoke pencil is a useful tool for what purpose related to duct leakage?

Measuring refrigerant subcooling
Measuring total external static pressure
Measuring CFM directly at a register
Visualizing air movement to help find leaks around joints and seams

Question 9: A supply duct running through an unconditioned crawlspace has a large disconnected joint. What is a likely symptom in the home above?

Rooms served by that duct run receive less airflow than designed, since air is escaping into the crawlspace instead
The equipment's rated static pressure automatically increases
The refrigerant charge automatically drops
No effect, since crawlspace air eventually rises into the home anyway

Question 10: Why is return-side duct leakage sometimes considered a bigger concern for indoor air quality than supply-side leakage?

Return leaks are always larger in size than supply leaks
Because a return leak pulls outside air, dust, or contaminants directly into the airstream that gets distributed through the whole house
Return leaks only occur in commercial buildings
Supply leaks never affect indoor air quality in any way

Question 11: Which of these is the best long-term method for sealing a duct seam?

Wrapping the seam in standard cloth duct tape only
Leaving the seam as-is since sealing is optional
Applying mastic over the seam, sometimes reinforced with mesh tape
Painting over the seam with regular wall paint

Question 12: A technician notices dust streaks around a return duct seam inside a mechanical closet. What does this often indicate?

The duct was recently cleaned
The refrigerant charge is low
The thermostat needs new batteries
Air is leaking at that seam, and dust in the air is depositing along the leak path over time

Question 13: A home has ductwork located entirely within conditioned space (inside the home's insulated envelope). How does this affect the consequences of duct leakage compared to ducts in an attic?

Leaked air generally stays within the conditioned space, so energy loss and comfort impact are usually smaller than with attic ductwork
Leakage inside conditioned space is always worse than leakage in an attic
Duct location has no effect on the consequences of leakage
This eliminates the need for any duct sealing at all

Question 14: What is a likely sign of significant supply duct leakage in an attic, noticed from inside the home?

Excessively strong airflow at every register
Weak airflow at registers even though the equipment and blower seem to be running normally
A sudden change in refrigerant type
The thermostat display turning off completely

Question 15: True or False: Sealing duct leaks can help both energy efficiency and indoor comfort at the same time.

False, sealing ducts has no measurable benefit
False, sealing only helps energy use, never comfort
True
True, but only for return ducts, never supply ducts

Question 16: A technician is deciding whether to prioritize sealing a small supply seam or a larger disconnected return joint on the same service call. Which is generally the higher priority?

The small supply seam, since supply leaks are always worse regardless of size
Neither should be sealed, since both are equally unimportant
It does not matter which is sealed first
The larger disconnected return joint, since it likely represents a bigger source of unconditioned air infiltration and lost performance

Question 17: What effect can duct leakage have on the temperature split (temperature difference) measured across the evaporator coil during a service call?

Duct leakage that changes the return air condition (for example, pulling in hot attic air) can throw off the expected temperature split
Duct leakage has no possible connection to temperature split readings
Duct leakage always increases the temperature split beyond normal
Temperature split can only be affected by refrigerant charge, never by ductwork

Question 18: Which statement about duct sealing materials is TRUE?

Standard cloth duct tape is the industry-preferred long-term duct sealant
Mastic and foil tape are generally more durable choices for sealing ducts than standard cloth duct tape
No sealing material lasts longer than a few days on any duct
Sealing materials have no effect on leakage rates

Question 19: A duct system has a moderate return leak pulling in attic air, and a moderate supply leak losing conditioned air, on the same branch. How would these two problems likely combine in terms of comfort in the served room?

The two leaks would cancel each other out with no net effect
Only the supply leak would matter, since return leaks have no effect on comfort
The room would likely receive less conditioned air than designed, and some of what it does receive may have already been affected by outside air infiltration on the return side
This combination is not physically possible in a real system

Question 20: What is a simple, low-cost first step to check for duct leakage during a routine service visit?

Immediately replace the entire duct system
Increase the thermostat setpoint by several degrees
Check only the refrigerant charge
Visually inspect accessible duct joints, seams, and connections for gaps, disconnections, or missing sealant

Question 21: A homeowner asks why sealing their attic ductwork would help lower their energy bill. What is the best explanation?

Sealing reduces the amount of conditioned air lost to the attic and the amount of hot or cold attic air pulled into the return, so the system works less to maintain comfort
Sealing ducts has no connection to energy use at all
Sealing ducts only affects the thermostat's display brightness
Sealing ducts always increases energy use

Question 22: True or False: A duct leak located close to the equipment (near the plenum) can affect airflow measurements taken at that same location.

False, leaks near the plenum never affect readings
True
False, only leaks far from the equipment matter
True, but only for supply plenum leaks, never return plenum leaks

Question 23: A technician applies mastic to a duct seam but the surface was dusty and not cleaned first. What is the likely result?

The mastic will bond even better because of the dust
There will be no difference in the outcome
The mastic may not adhere well, and the seal could fail sooner than expected
The refrigerant charge will be affected

Question 24: Which of the following best describes "duct leakage to outside" as a concept?

Air leaking between two rooms that are both fully conditioned
Refrigerant escaping from the lineset
Water leaking from the condensate drain
Air escaping from, or being pulled into, the duct system from spaces outside the conditioned living area, such as an attic, crawlspace, or garage

Question 25: What is a good practice after sealing a set of duct leaks, to confirm the repair worked?

Re-check airflow (CFM at registers) and/or static pressure to see if performance improved
Assume the repair worked without any further checks
Increase the refrigerant charge to compensate
Remove the mastic immediately after applying it

Question 26: A duct system was recently sealed, but static pressure did not change much afterward. What could this suggest?

This always means the mastic was applied incorrectly
The leaks sealed may not have been the main restriction, or other significant leaks or restrictions may remain unaddressed
This proves the duct system has no leaks at all
Static pressure and duct leakage are always directly proportional to each other

Question 27: True or False: Duct leakage can contribute to a room being pressurized or depressurized relative to the rest of the house.

False, duct leakage cannot affect room pressure at all
False, only closed doors can cause room pressure differences
True
True, but only in commercial buildings

Question 28: Which best summarizes why duct sealing is considered part of proper air distribution service, not just an optional extra?

Duct sealing is unrelated to airflow and only affects cosmetics
Duct sealing is only relevant to new construction, never service work
Duct sealing has no connection to energy efficiency
Leaky ducts directly reduce delivered airflow and waste energy, both of which are core concerns of air distribution performance

Question 29: A technician finds a return plenum with a gap around the filter rack, allowing unfiltered air to bypass the filter. What problem does this create, beyond airflow loss?

Unfiltered air (with dust and debris) can enter the system and reach the coil, reducing filtration effectiveness
This always increases the filter's MERV rating
This has no effect since the filter rack is not part of the sealed envelope
This only matters if the system uses an ECM blower motor

Question 30: Overall, what is the main goal of duct sealing in air distribution service?

To increase static pressure as much as possible
To keep conditioned air moving through the intended path, reducing wasted energy and unwanted air infiltration
To eliminate the need for a filter
To replace the need for balancing dampers

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)