20 Construction, Comfort & Airflow Practice Questions & Answers

1. 1. Why does a fibrous batt or blanket insulation slow heat flow through a wall or attic assembly?

   • A.It reflects essentially all radiant heat back toward its source regardless of how it is installed
   • B.It seals the cracks and penetrations in the assembly so outdoor air cannot leak through
   • C.It absorbs heat during the day and releases it outdoors at night
   • D.It traps air in many small pockets, which slows conduction and limits convection currents within the cavity✓ Answer

   Insulation works because still air is a poor conductor: the fibers divide the cavity air into small pockets so heat must move slowly by conduction through the fibers and trapped air, and convective looping inside the cavity is suppressed. That is why compressed, gapped, or misaligned insulation loses much of its rated performance.

   Source: NATE Core knowledge areas, basic construction — walls and ceilings, construction materialsReport a problem with this question

2. 2. An attic is fully insulated, yet the owner reports cold drafts and high winter heating bills; the attic hatch, wall top plates, and recessed-light penetrations are all open to the attic. What should the technician explain?

   • A.Adding a second layer of insulation over the same openings will stop the air movement
   • B.Air leakage matters only in summer, so nothing needs to be corrected before the heating season
   • C.The furnace should be replaced with a larger one so its extra capacity covers the leakage
   • D.Insulation slows conducted heat but does not stop air movement, so air sealing those openings is a separate job that must be done in addition to insulating✓ Answer

   Air sealing and insulating are two different jobs addressing two different heat-transfer paths: insulation resists conduction, while air sealing stops the mass movement of air that carries both heat and moisture. Fibrous insulation is air-permeable, so laying more of it over an unsealed hatch or top plate does not stop the leak.

   Source: NATE Core knowledge areas, basic construction — walls, ceilings and building materials; envelope air leakageReport a problem with this question

3. 3. During cold weather, indoor moisture migrates outward through a frame wall. Where does condensation occur inside that assembly, and what does that mean for vapour-retarder placement?

   • A.Condensation forms wherever the moist air reaches a surface at or below its dew point, so in a heating climate the retarder belongs on the side of the insulation that stays warm in winter✓ Answer
   • B.Condensation forms at the warmest surface in the wall, so the retarder belongs against the exterior sheathing in every climate
   • C.Condensation cannot occur inside a wall as long as the cavity is completely filled with insulation
   • D.Installing a vapour retarder on both faces of the wall is the reliable way to keep the cavity dry

   Water vapour condenses only when it contacts a surface at or below the dew point of that air, so the risk point in winter is the cold outer part of the cavity. Placing the retarder on the warm-in-winter side keeps indoor moisture from reaching that cold surface; sandwiching the cavity between two retarders traps any moisture that does get in and prevents drying in either direction.

   Source: NATE Core knowledge areas, basic construction — walls; vapour movement and condensation in building assembliesReport a problem with this question

4. 4. A homeowner with a large west-facing window wall wants replacement glazing that will most directly cut the late-afternoon cooling load caused by sunlight. Which rated window property governs that, and which way should it go?

   • A.A lower solar heat gain coefficient (SHGC), because SHGC is the fraction of incident solar radiation admitted through the glazing✓ Answer
   • B.A higher visible transmittance, because more daylight entering means less solar heat entering
   • C.A higher frame R-value, because the frame is what admits the sunlight
   • D.A higher U-factor, because U-factor is the rating that describes solar gain

   SHGC is the fraction of incident solar energy transmitted into the space, so lowering it directly reduces the solar portion of the cooling load — which is what dominates east- and west-facing glass at low sun angles. U-factor describes conducted heat flow (the inverse of R-value) and does little about a direct-sun problem.

   Source: NATE Core knowledge areas, basic construction — fenestration; NFRC window performance ratingsReport a problem with this question

5. 5. A planned supply trunk will not fit through the space between engineered roof trusses along its intended route. What is the correct action?

   • A.Leave every truss member intact and reroute or resize the duct, and if the structure must change, obtain approval from the truss designer or engineer of record first✓ Answer
   • B.Bore through the webs instead of notching them, since round holes do not weaken a truss
   • C.Cut one or two web members and reinforce the opening with sheet-metal straps
   • D.Notch the bottom chord just enough to pass the duct, because only the top chord carries roof load

   An engineered truss is a designed system in which every chord and web carries a calculated force, so cutting, notching, or boring any member destroys the load path the truss was designed around. The duct is the element that must move; any structural alteration is the truss designer's or engineer's call, not the installer's.

   Source: NATE Core knowledge areas, basic construction — girders and trussesReport a problem with this question

6. 6. On a set of residential plans, what does the clear span of a framed space tell the installing technician?

   • A.The total conditioned floor area used to size the equipment
   • B.The unobstructed distance between structural supports, which tells the technician how far a trunk duct or a piece of equipment can run before a bearing wall, girder, or column is in the way✓ Answer
   • C.The spacing between framing members such as studs or joists
   • D.The height from the finished floor to the underside of the ceiling

   Clear span is the unobstructed distance between supports, and it is the dimension that decides where trunk lines, plenums, and equipment can physically be placed without crossing a bearing element. Reading it from the plans before layout avoids discovering a girder or bearing wall in the middle of the intended duct run.

   Source: NATE Core knowledge areas, basic construction — plans and specifications; room specifications and clear spanReport a problem with this question

7. 7. Why does air infiltration in a hot, humid climate add to both the sensible and the latent portions of the cooling load?

   • A.Because infiltrating air always enters at a higher velocity than the supply air does
   • B.Because the outdoor air that leaks in must be both cooled down to room temperature, which is sensible heat, and dried of the moisture it carries, which is latent heat✓ Answer
   • C.Because leaking air raises the room's static pressure, and pressure is counted as latent heat
   • D.Because infiltration adds only latent load, while the sensible part comes entirely from the walls and roof

   Infiltrating outdoor air arrives at a different temperature and a different moisture content than room air. Bringing its temperature to the room condition is a sensible load, and condensing out the extra water vapour it carries is a latent load, which is why leaky houses in humid climates run high indoor humidity even when the space temperature is satisfied.

   Source: NATE Core knowledge areas, achieving desired conditions — role of humidity in comfort; sensible and latent load componentsReport a problem with this question

8. 8. Two bedrooms in the same house have identical floor area, but one faces west with a large window and is used as an office by two people with computer equipment. How does a proper load calculation treat them?

   • A.It ignores internal gains, because only the building envelope creates load
   • B.It treats them as equal, because floor area is what determines a room's load
   • C.It sizes each room's branch from the register size that is already installed
   • D.It calculates each room separately, because glazing area and orientation plus the heat given off by occupants and equipment change the room's load independently of its size✓ Answer

   A room-by-room load calculation adds up the actual gains and losses of that room: envelope area and construction, glazing area with its orientation and shading, infiltration, and internal gains from people, lighting, and equipment. Two rooms of the same size can therefore need very different airflow, which is exactly why floor area alone cannot size a branch duct or a register.

   Source: ACCA Manual J room-by-room load calculation practice, as referenced in NATE Core knowledge areas — achieving desired conditionsReport a problem with this question

9. 9. A ten-year-old system is being replaced in a house that has since been re-insulated and fitted with new windows. What should determine the capacity of the new equipment?

   • A.The nameplate capacity of the unit being removed, since it kept the house comfortable
   • B.The largest unit the existing electrical service and ductwork will accept
   • C.A load calculation of the house as it exists today, with equipment then selected to match that calculated load✓ Answer
   • D.A rule of thumb based on conditioned square footage

   Capacity must come from a load calculation of the building in its current condition, because the envelope improvements have already reduced the load the old unit was sized for. Copying the old nameplate or using an area rule of thumb carries forward an error and usually leaves the new system oversized, which hurts humidity control and cycling.

   Source: ACCA Manual J load calculation and Manual S equipment selection practice, as referenced in NATE Core knowledge areasReport a problem with this question

10. 10. In humid summer weather a house holds temperature easily but feels damp and clammy; the system satisfies the thermostat in short bursts, and measured airflow, charge, and coil condition are all normal. What is the most likely cause?

    • A.The thermostat setpoint is too low for the outdoor conditions
    • B.The equipment is oversized for the load, so it short cycles and never runs long enough for the coil to remove much moisture✓ Answer
    • C.The equipment is undersized and cannot reach the setpoint
    • D.The return grilles are too large for the system

    Moisture removal is a function of runtime: the coil must stay wet and cold long enough for vapour to condense and drain away. An oversized system meets the sensible load quickly and shuts off, so the space ends up cool but humid — the classic clammy complaint that no amount of lowering the setpoint will fix.

    Source: NATE Core knowledge areas, achieving desired conditions — humidity and adjusting system performance for humidity controlReport a problem with this question

11. 11. In winter an occupant seated beside a large window says she feels cold, although a thermometer next to her chair reads the same as the rest of the house. What is the best explanation?

    • A.The thermometer must be out of calibration
    • B.Her body is losing heat by radiation to the cold glass surface, so the mean radiant temperature around her is lower than the air temperature✓ Answer
    • C.Air is stratifying so severely that the air at her head is far warmer than the air at her feet
    • D.Low relative humidity has raised her dew point

    Comfort depends on air temperature, humidity, air movement, and mean radiant temperature — the average temperature of the surfaces exchanging radiant heat with the body. A large cold window pulls radiant heat from the occupant even when the air temperature is correct, so the fix is at the surface (better glazing, drapes, or a supply outlet washing the glass), not at the thermostat.

    Source: NATE Core knowledge areas, achieving desired conditions — role of temperature in comfort; mean radiant temperatureReport a problem with this question

12. 12. At the same dry-bulb temperature, why does a space at high relative humidity feel warmer and less comfortable to its occupants?

    • A.Because moist air conducts heat away from the skin faster than dry air does
    • B.Because moist air slows the evaporation of perspiration, and evaporation is one of the main ways the body sheds heat✓ Answer
    • C.Because high humidity increases air movement across the skin
    • D.Because water vapour raises the dry-bulb temperature of the air itself

    The body rejects heat by conduction, convection, radiation, and evaporation. When the surrounding air already holds a lot of vapour, the evaporation path slows down, less body heat leaves, and the occupant feels warmer than the thermometer suggests — which is why humidity control, not just temperature, is part of delivering comfort.

    Source: NATE Core knowledge areas, achieving desired conditions — role of humidity in comfort; body heat transfer mechanismsReport a problem with this question

13. 13. Responding to a humidity complaint, a technician raised the indoor blower to the highest speed the equipment allows. What will that do to moisture removal in cooling?

    • A.Dehumidification gets worse, because higher airflow raises the coil surface temperature and the sensible heat ratio, so less vapour condenses on the coil✓ Answer
    • B.Dehumidification improves, because higher airflow lowers the coil temperature
    • C.Dehumidification is unaffected, because latent removal depends only on the refrigerant charge
    • D.Dehumidification improves, because more air passes across the coil every minute

    Latent capacity depends on how far the coil surface sits below the entering air's dew point. Raising airflow warms the coil and shifts capacity toward sensible cooling, so the space gets colder but stays damp; moving airflow down toward the low end of the manufacturer's allowed range is what increases dehumidification, and going below what the manufacturer permits risks a frosted coil.

    Source: NATE Core knowledge areas, achieving desired conditions — adjusting system performance for humidity controlReport a problem with this question

14. 14. A homeowner has pushed a sofa against the only return grille and keeps the bedroom doors closed against undercut-free thresholds. What happens to the cooling system?

    • A.Airflow through the coil falls, the coil runs colder, delivered capacity drops, and in cooling the coil can eventually frost✓ Answer
    • B.Only the sound level changes; performance is unaffected
    • C.Static pressure across the blower drops while airflow stays the same
    • D.Airflow rises, because the blower works harder against the obstruction

    A blocked or closed return path is a restriction: static pressure across the air handler climbs and airflow falls. With less air crossing the coil, the coil surface temperature drops, less heat is carried away, capacity and dehumidification both suffer, and severe starvation can lead to a frosted coil. Restoring a return path — clearing the grille and providing transfer air for closed doors — is the fix.

    Source: NATE Core knowledge areas, achieving desired conditions and air distribution — return air path and system airflowReport a problem with this question

15. 15. Ducts run through a vented attic in a hot, humid climate during the cooling season. Which duct leak does the most damage to indoor humidity?

    • A.A supply leak inside a conditioned basement
    • B.A small supply leak inside the conditioned living space
    • C.A return leak in the hot, humid attic, because it draws moist attic air into the system and adds both sensible and latent load to every cycle✓ Answer
    • D.A leak at a register boot that discharges into the room it serves

    Leakage matters most where the duct is outside the conditioned space and the leak direction pulls unconditioned air in. A return leak in a vented attic continuously mixes hot, moisture-laden air into the return stream, raising the load the coil must handle and driving indoor humidity up; leaks that stay inside the conditioned envelope waste far less. Ducts outside conditioned space must be sealed with an approved sealant and insulated.

    Source: NATE Core knowledge areas, achieving desired conditions — air distribution, duct leakage and ducts in unconditioned spaceReport a problem with this question

16. 16. Which statement correctly describes the pressures in an operating supply duct?

    • A.Velocity pressure acts in all directions, and total pressure can only be measured at the return grille
    • B.Static and velocity pressure are the same quantity, simply read with different instruments
    • C.Total pressure is the sum of static pressure and velocity pressure; static pressure acts equally in all directions, while velocity pressure acts only in the direction of flow✓ Answer
    • D.Total pressure equals static pressure minus velocity pressure, and static pressure acts only in the direction of flow

    Total pressure is static plus velocity pressure. Static pressure is the outward push of the air on the duct wall and is sensed equally in every direction, while velocity pressure exists only because the air is moving and is sensed facing into the stream — which is why a pitot tube reads total pressure at its tip and static pressure at its side ports, and the difference between them is velocity pressure.

    Source: NATE Core knowledge areas, air flow and measurements — static, velocity and total pressureReport a problem with this question

17. 17. On a system with a fixed-speed blower, a technician finds a heavily loaded filter and an undersized return, and measures an unusually high external static pressure. What is happening to airflow and to capacity?

    • A.Airflow is unaffected; high static pressure only shows that the blower is working properly
    • B.The added restriction moves the blower up its performance curve so airflow falls, and with less air crossing the coil or heat exchanger less heat is carried away, so delivered capacity drops✓ Answer
    • C.Airflow falls but capacity is unchanged, because the refrigerant charge is correct
    • D.Airflow rises along with static pressure, so capacity increases

    A blower delivers less air as the resistance it must overcome increases; that is what a fan curve describes. Since the air is the medium that carries heat to or from the room, reduced airflow always means reduced delivered capacity, a colder coil in cooling, and higher temperature rise in heating — so the cure is to remove restriction (clean or enlarge the filter, correct the return), not to accept the high reading.

    Source: NATE Core knowledge areas, air flow — external static pressure, system resistance and blower performanceReport a problem with this question

18. 18. A ceiling supply register in a bedroom whistles and roars whenever the system runs; the branch duct and the register face are both small for the air that room needs. What is the correct fix?

    • A.Add a long flexible duct with several tight bends ahead of the register to absorb the noise
    • B.Reduce the blower speed for the entire house so the one room quiets down
    • C.Reduce the face velocity by upsizing the branch duct and the register to the airflow the room actually needs, and smooth the fitting feeding it✓ Answer
    • D.Close the balancing damper at that register until the noise stops

    This is airflow-generated noise, not equipment noise: whistle and roar come from excessive face velocity and turbulence, so the cure is to give the same airflow more area. Choking the damper only shifts the noise to the damper and starves the room, and dropping the blower speed penalizes the whole system to mask one bad branch.

    Source: NATE Core knowledge areas, achieving desired conditions — sound from airflow sources; register and grille selectionReport a problem with this question

19. 19. A customer with a one-inch filter slot and an already-high external static pressure asks for much finer filtration. What should the technician explain about moving to a higher MERV filter?

    • A.A higher MERV filter captures finer particles but also adds resistance, so the filter area must be increased — a larger or deeper media cabinet — to gain the finer filtration without cutting airflow further✓ Answer
    • B.A higher MERV filter is always the right upgrade, because filtration cannot affect airflow
    • C.MERV is a rating of pressure drop, so a higher MERV filter has a lower pressure drop
    • D.Filtration and airflow are unrelated, because only the coil affects static pressure

    MERV rates particle-capture efficiency, not resistance, and finer media generally resists airflow more for a given face area. Because system airflow falls as resistance rises, the way to add filtration safely is to add media area — a deeper or larger filter cabinet — so face velocity and pressure drop stay low; verifying static pressure and airflow after the change is part of the job.

    Source: NATE Core knowledge areas, achieving desired conditions — air quality and air cleaning; filter pressure drop and system airflowReport a problem with this question

20. 20. A tight new house in a hot, humid climate needs continuous mechanical ventilation. Which approach best limits the moisture that the ventilation air brings indoors, and why?

    • A.A heat recovery ventilator (HRV), because it transfers moisture as well as heat between the two air streams
    • B.A continuously running exhaust fan alone, because depressurizing the house keeps outdoor humidity from entering
    • C.A heat recovery ventilator (HRV), because it dehumidifies the incoming air down to the indoor dew point
    • D.An energy recovery ventilator (ERV), because it exchanges both heat and moisture between the outgoing and incoming streams, so less outdoor humidity is carried into the house✓ Answer

    An HRV exchanges sensible heat only, while an ERV core also transfers moisture, so in a humid climate the ERV pre-dries the incoming air toward indoor conditions and reduces the latent load the cooling system must handle. Note that neither device is a dehumidifier, and exhaust-only ventilation depressurizes the house, which can pull in unconditioned humid air and risks backdrafting an atmospherically vented combustion appliance.

    Source: NATE Core knowledge areas, achieving desired conditions — ventilation for comfort and air quality; heat versus energy recovery ventilationReport a problem with this question

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