HVAC Sheet Metal and Fabrication 4

Question 1

What does the term 'duct aspect ratio' refer to, and why does it matter?

Accepted Answer

The ratio of duct width to height; high ratios increase friction loss

Answer

Aspect ratio is the width-to-height ratio of rectangular duct; ratios above 4:1 significantly increase friction losses and material use.

Question 2

When fabricating a conical reducer in round ductwork, what maximum taper angle minimizes turbulence?

Accepted Answer

15 degrees or less per side

Answer

Keeping the taper angle to 15 degrees or less per side (30 degrees total included angle) minimizes flow separation and turbulence in a conical reducer.

Question 3

What is a 'snap lock' seam used for in HVAC sheet metal fabrication?

Accepted Answer

Joining round duct spiral seam longitudinally

Answer

The snap lock seam is the longitudinal seam used on spiral wound round duct, formed continuously by interlocking the strip edges as it is wound.

Question 4

Which material is NOT typically acceptable for use as HVAC duct in a commercial building per IMC/SMACNA?

Accepted Answer

PVC plastic

Answer

PVC plastic duct is generally not acceptable for supply and return HVAC systems in commercial buildings due to flammability concerns, though it may be allowed for specific exhaust applications.

Question 5

A duct system tested at 1.0 inch WC positive pressure is classified under SMACNA as what pressure class?

Accepted Answer

1-inch WC (low pressure)

Answer

SMACNA classifies duct systems tested at 1.0 inch WC as the 1-inch pressure class, requiring specific gauge and reinforcement standards.

HVAC Practice Test

HVAC Practice Test

HVAC Sheet Metal and Fabrication 4