Nevada C-13 Sheet Metal Contractor Examination

Under NAC 624.300, which task is outside the Nevada C-13 sheet-metal classification?

• AFabricating and installing a galvanized rain leader and downspout
• BInstalling a packaged rooftop unit that uses refrigeration as an integral part of the sys…
• CForming and installing a standing-seam metal roof panel system
• DFabricating a stainless-steel steam-table pan for food-service equipment

How are airflow (CFM), average velocity (FPM), and internal cross-sectional area (square feet) related in a sheet-metal duct?

• ACFM equals velocity plus area
• BCFM equals velocity divided by area
• CCFM equals area times velocity (Q = A × V)
• DCFM equals area minus velocity

A rectangular galvanized duct measures 20 inches wide by 16 inches high and carries 2,000 CFM. What is the average air velocity?

• A720 feet per minute
• B900 feet per minute
• C1,150 feet per minute
• D1,440 feet per minute

A 14-inch inside-diameter round spiral duct carries 1,200 CFM. What is the approximate average velocity?

• A780 feet per minute
• B980 feet per minute
• C1,120 feet per minute
• D1,470 feet per minute

An 18-inch by 12-inch rectangular branch is designed to run at 800 FPM. What airflow does that duct carry?

• A800 CFM
• B1,000 CFM
• C1,200 CFM
• D1,600 CFM

Per 2018 UMC Section 601.2, blower-type heating, cooling, and ventilation duct systems shall be sized in accordance with which method?

• AACCA Manual D, or other approved methods
• BAny shop rule of thumb posted at the brake
• COnly equal-friction charts printed on the fan carton
• DOnly the International Residential Code Appendix M

Under 2018 UMC Section 603.4.1, what is the maximum length of a factory-made flexible air duct or connector used as an elbow at a terminal device in a commercial building?

• A3 feet
• B5 feet
• C14 feet
• D25 feet

Per the 2018 UMC, plastic air ducts and fittings are limited to which installation and maximum design temperature?

• AUnderground installations only, 150°F
• BExposed rooftop mains, 180°F
• CGrease ducts serving Type I hoods, 250°F
• DAbove-grade supply only, 200°F

Which shop-formed longitudinal seam is the usual lock on rectangular galvanized HVAC duct?

• AStanding-seam roof clip
• BGrooved lock used only on copper roofing
• CPittsburgh lock
• DDovetail lock used only on round spiral

In SMACNA-style rectangular low-pressure duct, which transverse joint uses a flat S-slip on the long sides and drive cleats on the short sides?

• AS-and-drive (flat S-cleat) joint
• BTDC/TDF 4-bolt flange only
• CCompanion-angle bolted flange
• DWelded standing seam

SMACNA duct-design practice recommends keeping the aspect ratio of a rectangular duct at or below which value whenever space allows?

• A2 to 1
• B4 to 1
• C8 to 1
• D12 to 1

A 30-inch by 10-inch duct must deliver 2,500 CFM at 1,200 FPM. Does this size meet that design point?

• ANo; a 30-by-10 has only 1.50 square feet
• BNo; 2,500 CFM at 1,200 FPM requires 3.00 square feet
• CYes, but only if the duct is lined
• DYes; the area is 2.08 square feet and 2,500 ÷ 2.08 = 1,200 FPM

When should a square (mitered) rectangular elbow have turning vanes for acceptable pressure loss?

• AOnly on return ducts under 400 FPM
• BWhen a full-radius throat cannot be used and a square throat would otherwise create a hig…
• CNever; vanes are decorative only
• DOnly when the duct is aluminum

What maximum hanger spacing does SMACNA HVAC Duct Construction Standards commonly allow for horizontal rectangular sheet-metal duct, unless a heavier construction table says otherwise?

• A4 feet
• B6 feet
• C10 feet
• D16 feet

How must a SMACNA duct construction pressure class relate to the system’s design operating pressure?

• AAll ducts may be built to 1/2 inch w.g. regardless of fan rating
• BNegative-pressure ducts have no pressure class
• CThe construction class may be half the design pressure if the fan is downstream
• DThe construction pressure class shall equal or exceed the design operating pressure of th…

Which closure system is the listed method for sealing a UL 181 factory-made flexible air duct?

• AOrdinary cloth duct tape with no listing mark
• BOnly soldering the inner liner
• CA UL 181B-listed tape or mastic, plus a listed mechanical fastener
• DOnly sheet-metal screws through the vapor jacket with no sealant

In conventional low-velocity HVAC design, supply mains are typically kept at or below about which velocity to control noise and friction?

• A400 feet per minute
• B2,000 feet per minute
• C4,000 feet per minute
• D6,500 feet per minute

Under SMACNA HVAC Duct Construction Standards, Seal Class A requires sealing which of the following?

• ATransverse joints only
• BLongitudinal seams only
• CAll transverse joints, all longitudinal seams, and all duct-wall penetrations
• DHanger straps only

Per 2018 UMC Section 603.10.1, duct leakage tests required for systems at 3 inches water column and higher begin on representative sections totaling not less than what share of the installed duct area?

• A5 percent, then 15 percent if that sample fails
• B10 percent, then 40 percent if that sample fails, then 100 percent if the second sample f…
• C50 percent of every riser only
• D100 percent of every system regardless of the first result

Per the 2018 UMC, metal duct installed in or under a concrete slab, or near earth, shall have not less than which separation from earth?

• A1 inch
• B2 inches
• C4 inches
• D12 inches

Why are large rectangular duct sides commonly cross-broken or beaded in the shop?

• ATo increase panel stiffness and reduce oil-canning
• BTo raise the duct pressure class by one step
• CTo replace required hangers
• DTo convert the duct to a grease duct

A 20-inch by 8-inch rectangular duct and a 14-inch round duct have nearly the same internal area. Which statement is correct?

• AThe rectangular duct always has lower friction because it is flatter
• BEqual area means equal hydraulic diameter and equal friction regardless of shape
• CThe round duct has less perimeter for the same area, so it usually has lower friction and…
• DOnly the rectangular duct may be used on a supply system

An 18-inch inside-diameter round duct is to run at 800 FPM. What airflow does it carry?

• A800 CFM
• B1,130 CFM
• C1,410 CFM
• D1,880 CFM

For a low-loss branch takeoff from a rectangular main, which fitting is preferred over a raw hole with a raw spin-in and no scoop?

• AA 45-degree shoe or conical takeoff with a damper, or a spin-in with an extractor scoop a…
• BA tee cut flush with no damper
• CA 90-degree mitered stub with no throat radius
• DA flexible-duct stab through an unsealed hole

What is the primary purpose of a volume damper in a sheet-metal branch?

• ATo replace the need for turning vanes
• BTo increase the duct pressure class
• CTo balance airflow to the design CFM of that branch
• DTo serve as a fire damper

A 36-inch by 18-inch rectangular main carries 3,600 CFM. What is the average velocity?

• A600 feet per minute
• B800 feet per minute
• C1,000 feet per minute
• D1,200 feet per minute

SMACNA galvanized HVAC duct tables assume lock-forming-quality steel conforming to ASTM A653/A924 with which typical zinc coating as the baseline?

• AG-30 only
• BG-60
• CUncoated black iron for all indoor supply
• DHot-dip G-235 bridge steel

A 48-inch by 8-inch duct and a 24-inch by 16-inch duct have the same 2.67-square-foot area. Which statement is correct about the 48-by-8?

• AIt has a 6:1 aspect ratio, more perimeter, higher friction, and needs more reinforcement…
• BIt has a lower aspect ratio and less metal than the 24-by-16
• CEqual area means identical SMACNA gauge and hanger tables
• DThe 48-by-8 is preferred whenever space allows

How should factory-made flexible duct be supported so it does not collapse or sag excessively?

• ASupport at not more than about 4 to 5 feet on center with a wide saddle, keeping sag to a…
• BHang it from a single wire at midspan only
• CStretch it tight between fittings with no saddles
• DSupport it only at the air-handler end

What is the usual shop-formed longitudinal seam on round spiral duct?

• AA Pittsburgh lock running the length of the pipe
• BA helical lockseam rolled as the pipe is formed
• CA soldered grooved lock used on copper gutters
• DA standing-seam roof clip

When a supply or return duct penetrates a fire-resistance-rated wall or floor assembly, which device is required unless an exception in the code applies?

• AA listed fire damper installed in accordance with its listing
• BAn ordinary volume damper taped shut
• CA flexible-duct connector in the plane of the wall
• DA backdraft damper only

A 22-inch by 14-inch rectangular branch is designed for 900 FPM. What airflow does it carry?

• A1,540 CFM
• B1,730 CFM
• C1,925 CFM
• D2,200 CFM

Where is external duct wrap insulation placed on a supply duct that runs through an unconditioned attic?

• AOn the outside of the metal, with joints sealed so the vapor retarder is continuous
• BOnly on the inside as a liner, never outside
• CBetween the hangers and the structure only
• DNowhere; attic ducts are never insulated

Which listed metal vent is intended for listed, draft-hood or fan-assisted Category I gas appliances?

• AType B double-wall gas vent
• BSingle-wall black stovepipe used as a complete gas-vent system through a concealed space
• CType L vent used only for listed oil appliances, with no gas listing
• DA Type I grease duct

Per 2018 UMC chimney termination rules for residential-type or low-heat appliances, the chimney shall extend not less than which combination above the roof?

• A1 foot above the roof and 1 foot above anything within 5 feet
• B3 feet above the highest point where it passes through the roof and 2 feet above any port…
• C10 feet above the roof regardless of nearby walls
• DFlush with the shingles if a rain cap is used

A Type B or Type L vent shall terminate not less than which vertical height above the highest connected appliance draft hood or flue collar?

• A2 feet
• B3 feet
• C5 feet
• D10 feet

What is the typical listed clearance to combustibles for Type B double-wall gas vent?

• A1 inch
• B6 inches
• C18 inches
• D36 inches

Per 2018 UMC Section 802.10.6, a vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney not less than which pitch?

• A1/16 inch per foot
• B1/8 inch per foot
• C1/4 inch per foot
• D1 inch per foot

Per 2018 UMC Section 802.6.2.2, Type B and Type L vents shall extend in a generally vertical direction with offsets not exceeding which angle, except that one offset of which larger angle is permitted?

• A30 degrees, except one 45-degree offset
• B45 degrees, except one 60-degree offset
• C60 degrees, except one 90-degree offset
• D90 degrees with no limit on the number of offsets

A draft-hood appliance is served by a Type B vent that is 16 feet high. Per 2018 UMC Section 802.6.2.2, the total horizontal distance of the vent plus the horizontal vent connector shall not exceed which length?

• A8 feet
• B12 feet
• C16 feet
• D24 feet

Per 2018 UMC Section 802.6.1.5, a gas vent that passes through a roof shall terminate with which device?

• AA listed vent cap or listed roof assembly
• BAn open pipe with no cap
• CA masonry chimney pot only
• DA Type I upblast grease fan

A mechanical-draft venting system shall terminate not less than which distance above a forced-air inlet located within 10 feet?

• A1 foot
• B2 feet
• C3 feet
• D8 feet

Why may a single-wall metal vent connector not be used in a concealed space the way Type B pipe may?

• ASingle-wall connector typically requires about 6 inches to combustibles and is not a list…
• BSingle-wall pipe is listed for zero clearance in walls
• CSingle-wall pipe has a lower flue temperature than Type B
• DThe UMC requires single-wall pipe in every chase

A factory-built (patented) metal chimney installed under the C-13 scope shall be listed to which standard and installed how?

• AUL 103 or the applicable chimney listing, installed with the listed clearances, supports,…
• BASTM A653 only, with no listing required
• CUL 181, the flexible-duct standard
• DAny unlisted shop-built pipe of 30-gauge galvanized

Type B gas vent is listed for which appliances?

• AListed Category I gas appliances with draft hoods or fan-assisted vents
• BSolid-fuel wood stoves as a complete chimney
• COil-fired appliances that require Type L only, with no gas listing
• DType I commercial fryers