HVAC Sheet Metal and Fabrication 2 — Questions and Answers
Question 1: What is the standard gauge thickness for residential HVAC supply ductwork in low-pressure systems?
- 26 gauge (Correct answer)
- 22 gauge
- 18 gauge
- 30 gauge
Correct answer: 26 gauge
26 gauge galvanized steel is the standard minimum thickness for residential low-pressure supply ductwork per SMACNA guidelines.
Question 2: Which type of joint is used to connect two sections of rectangular duct end-to-end in the field?
- S-slip and drive cleat (Correct answer)
- Pittsburgh seam
- Grooved seam
- Lap joint
Correct answer: S-slip and drive cleat
The S-slip and drive cleat connection is the standard field joint for rectangular duct sections, providing secure mechanical attachment.
Question 3: When fabricating a 90-degree elbow for round ductwork, what is the primary advantage of a gored elbow over a stamped elbow?
- Lower airflow resistance (Correct answer)
- Lower material cost
- Easier field assembly
- Better fire resistance
Correct answer: Lower airflow resistance
Gored elbows have a larger radius and fewer abrupt direction changes, resulting in lower static pressure loss compared to stamped elbows.
Question 4: What does the term 'flat pattern development' mean in sheet metal fabrication?
- Laying out the 2D shape that will be bent into a 3D fitting (Correct answer)
- Smoothing the metal surface before cutting
- Creating a CAD drawing of the finished duct
- Planning the duct routing on a floor plan
Correct answer: Laying out the 2D shape that will be bent into a 3D fitting
Flat pattern development is the process of calculating and drawing the unfolded shape of a fitting on flat sheet metal before cutting and forming.
Question 5: Which hand tool is used to close the Pittsburgh lock seam on rectangular duct?
- Hammer and bar folder (Correct answer)
- Tin snips
- Nibbler
- Slip roll
Correct answer: Hammer and bar folder
A mallet and a bar folder or hand seamer are used to close the Pittsburgh lock seam by folding the male edge into the female pocket.
Question 6: What is the purpose of adding a standing seam reinforcement to a large rectangular duct panel?
- Prevent oil-canning and panel flutter (Correct answer)
- Improve thermal insulation
- Reduce noise from airflow turbulence
- Increase duct airtightness
Correct answer: Prevent oil-canning and panel flutter
Standing seam reinforcements stiffen large flat duct panels to prevent oil-canning (drumming) caused by pressure fluctuations.
Question 7: According to SMACNA, what is the maximum recommended length for a flexible duct connector at a fan unit?
- 12 inches (Correct answer)
- 36 inches
- 6 inches
- 48 inches
Correct answer: 12 inches
SMACNA recommends flexible duct connectors at fan units be limited to 12 inches to isolate vibration without excessive pressure drop.
HVAC Sheet Metal and Fabrication 2
What is the standard gauge thickness for residential HVAC supply ductwork in low-pressure systems?