Sheet Metal and Fabrication Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Sheet Metal and Fabrication flashcards as text
What is the primary reason galvanized steel is the most common material for HVAC ductwork?
Answer: It provides corrosion resistance without requiring additional coatings
The zinc coating on galvanized steel provides inherent corrosion resistance, making it durable and cost-effective for most HVAC duct applications.
Which fitting is used to offset duct around an obstruction while maintaining the same duct size?
Answer: Offset fitting
An offset fitting shifts the duct laterally or vertically to route around a beam, pipe, or other obstruction while keeping the same duct dimensions.
When a wye fitting splits a round duct into two branches, what should the combined cross-sectional area of the branches equal for proper air distribution?
Answer: Approximately equal to or greater than the main trunk area
The combined area of the two branches should at least equal the main trunk area to avoid excessive velocity increase and pressure loss at the split.
What type of mastic sealant is recommended for sealing HVAC duct joints in unconditioned spaces?
Answer: UL 181-listed water-based duct mastic applied with mesh tape
UL 181-listed duct mastic reinforced with fiberglass mesh tape provides a durable, airtight seal that remains flexible across temperature cycles in unconditioned spaces.
What is 'parallel pattern development' used for in HVAC sheet metal layout?
Answer: Developing the flat pattern of cylinders and prisms that have parallel lateral edges
Parallel pattern development (parallel line development) is used to unfold fittings such as cylinders, rectangular ducts, and elbows whose lateral edges are parallel.
A duct hanger rod for a rectangular duct should be sized based on which primary factor?
Answer: The weight of the duct and any insulation it must support
Hanger rods are sized by the load they must support, which is determined by the weight of the duct section (and insulation) between hanger points.
When fabricating a square-to-round transition, which development method is most appropriate?
Answer: Triangulation method
The triangulation method is used for square-to-round transitions because the surfaces are warped (non-developable) and must be divided into triangles to approximate the flat pattern.