Sheet Metal Worker Red Seal duct installation and air balancing practice questions (308A).

Five free practice questions on duct installation and air balancing: block C of the Red Seal 308A Sheet Metal Worker exam, about 41 of its 120 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Recall · Installs registers, grilles, diffusers and louvers

   On a mechanical drawing's air outlet schedule, one wall outlet is listed as a register and another as a grille. What does the register have that the grille does not?

   1. A volume damper behind its face.
   2. Blades that spread air in a radial pattern.
   3. Drainable blades that shed rain.
   4. A hinged face that holds a filter.
   Show the answer

   A. Correct. A register is a grille with a built-in volume damper (usually opposed blades behind the face) so the airflow at that outlet can be adjusted or shut off. A grille is only the louvred face, so any balancing is done with a damper in the branch duct.

   Why not the others

   B. Spreading air in several directions from the face is what a diffuser does, typically in a ceiling. A register is defined by its damper, not by its discharge pattern; a wall register throws air in one direction like a grille.

   C. Drainable, rain-shedding blades belong to a louver on an outside wall. Registers and grilles are indoor outlets and inlets; the difference between them is the damper behind the register's face.

   D. A hinged face with a filter behind it is a filter grille, used on returns. It is still a grille; what makes an outlet a register is the volume damper fitted behind the face.

   Source: Red Seal Occupational Standard, sub-task C-11.05

2. Procedural · Installs penetrations and sleeves

   A 4 in. round opening for a new exhaust collar is to be cut in an installed 18 gauge (0.050 in.) stainless steel kitchen wall panel. Which method gives a clean hole?

   1. An oxy-fuel torch with a small cutting tip.
   2. A hole saw at high speed with cutting fluid.
   3. Aviation snips worked from a drilled starter hole.
   4. A hole saw at low speed with cutting fluid.
   Show the answer

   D. Correct. Stainless steel work-hardens when it heats and rubs, so it is cut at low speed with firm, steady feed and cutting fluid. The hole saw leaves a round, clean edge in the thin panel without distorting it.

   Why not the others

   A. Oxy-fuel cutting depends on the steel oxidizing, and stainless steel's chromium stops that, so the torch only melts a ragged hole and heat-damages the panel. It is not a stainless cutting method.

   B. Cutting fluid helps, but high speed overheats the teeth and the stainless work-hardens under them, so they glaze, dull and stop cutting, and the panel can discolour. Stainless is cut at low speed with firm, steady feed.

   C. Snips on an installed stainless panel leave a rough, wavy edge and bend the thin sheet around the hole, a poor seat for the collar. A hole saw cuts it clean and round.

   Source: Red Seal Occupational Standard, sub-task C-9.03

3. Recall · Connects appliances or mechanical equipment to chimney and breeching

   A homeowner's insurer will not cover a new wood stove until its connector and chimney have been inspected by a certified person. Which certification do insurers commonly look for?

   1. An oil burner technician certificate.
   2. A sheet metal journeyperson certificate.
   3. A CWB welding certification.
   4. A WETT certification.
   Show the answer

   D. Correct. WETT (Wood Energy Technology Transfer) is the Canadian non-profit that trains and certifies installers, inspectors and chimney sweeps for wood-burning systems, and insurers commonly ask for a WETT inspection of a new wood stove installation.

   Why not the others

   A. An oil burner technician certificate covers oil-burning equipment, not wood-burning systems. Insurers looking at a wood stove ask for an inspector certified for wood energy.

   B. A sheet metal certificate qualifies a worker in the trade, including installing chimneys and connectors, but it is not a wood-energy inspection credential. Insurers commonly ask for a WETT-certified inspection.

   C. CWB certification qualifies welders and welding companies to its standards. It says nothing about inspecting a wood stove's connector and chimney.

   Source: Red Seal Occupational Standard, sub-task C-10.02; CWB

4. Procedural · Installs pneumatic and gravity material handling system components

   A pneumatic system conveying fine combustible dust has a rubber flexible connector between two metal duct sections. The specification requires every conductive part to be bonded and grounded. What is installed at the connector?

   1. A second clamp band added at each end of the connector.
   2. An isolating gasket fitted under each of the clamp bands.
   3. A bead of sealant run over each of the two clamp bands.
   4. A jumper wire from one metal section to the other.
   Show the answer

   D. Correct. Dust sliding through the duct builds up static charge. The rubber connector breaks the metal path, so the section beyond it can charge up and spark across to grounded metal, an ignition source in combustible dust. A jumper across the connector keeps the whole run bonded to ground.

   Why not the others

   A. A second band strengthens the clamp, but the bands bear on the rubber, which does not conduct. The duct sections on each side are still not bonded to each other.

   B. Isolation is what dissimilar metals need against galvanic corrosion; here it does the opposite of what the specification asks, leaving metal electrically floating where static can build up.

   C. Sealant keeps dust in and air out at the clamps, but it is not a conductor. The connector still breaks the bonding path between the two duct sections.

   Source: Red Seal Occupational Standard, sub-task C-12.01

5. Procedural · Performs testing, adjusting and balancing (TAB)

   A new constant-volume supply system is ready for air balancing. Before the first airflow readings are taken, what is checked?

   1. That branch dampers are preset to their final positions.
   2. That dampers are open and filters and coils are clean.
   3. That the fan runs at the highest speed its motor allows.
   4. That the outlets at the end of each run are throttled.
   Show the answer

   B. Correct. Readings taken with a damper shut, a fire damper closed or a loaded filter or dirty coil describe a fault, not the system. Confirming that every damper is open and the filters and coils are clean means the balance starts from the system as designed.

   Why not the others

   A. Final damper positions are what balancing finds; they cannot be known before the readings. The dampers start open, and branches are then adjusted from measured flows.

   C. Running the fan flat out can overload the motor and gives readings that have nothing to do with design. Fan speed is set from measured airflow against design, after the system is checked.

   D. Throttling outlets before any readings forces flow without knowing where it is short or in excess. Outlets are adjusted only after the system airflows have been measured.

   Source: Red Seal Occupational Standard, sub-task C-14.02

02Answer key

03What block C covers

Putting air and material handling systems into the building: site measurements, demolition, penetrations, supports, hangers and seismic restraints, chimneys, breeching and condensing appliance venting, air handlers, rooftop units and HRVs, duct, dampers, fire and smoke dampers, grilles and diffusers, VAV boxes, coils, filters and plenums, dust collection and conveying, insulation and cladding, then leak testing, air balancing (TAB) and commissioning.

The Red Seal Occupational Standard names this block “Installs air and material handling systems”. It carries 34.2% of the exam, about 41 of the 120 questions, split across six tasks. The share column is each task's weight within the block, as the standard publishes it.

04What the questions turn on

Fire dampers must stay free

Duct joins a fire damper sleeve with a listed breakaway connection, and the stated gap round the sleeve is left open so the sleeve can expand in a fire. A damper labelled for wall installation does not go into a floor.

Area times velocity is airflow

Airflow in cfm is area in square feet times velocity in fpm. A lined duct is checked on its clear area inside the liner. A grille's face is sized up by dividing by its free-area percentage, while a duct counts as 100 % free area.

Balance from the weakest outlet

In the proportional method the outlet reading the lowest percentage of its design stays wide open, and the others are throttled to match it. Airflow follows fan speed, so 12 % more air needs 12 % more rpm.

Condensate drains back, not out

A condensing furnace's plastic vent slopes back toward the furnace at the maker's rate so condensate reaches its trap. A low point gets a drain tee with a trapped line, and stove connector crimps point down toward the stove.

05The other blocks

The 308A exam has five blocks. Each has its own page of free questions:

The 308A Sheet Metal Worker practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.