Ductwork 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 Ductwork flashcards as text
When retrofitting insulation on existing sheet metal ducts in an unconditioned attic, what minimum R-value does IECC 2021 typically require for climate zones 4 and above?
Answer: R-8
IECC 2021 requires a minimum of R-8 duct insulation for ducts in unconditioned spaces in climate zones 4 and above to limit thermal losses.
What is 'duct conduction loss' and how does it affect system efficiency?
Answer: Heat transfer through duct walls that warms or cools supply air before it reaches registers
Duct conduction loss occurs when heat flows through duct walls between conditioned supply air and surrounding unconditioned space, reducing the effective capacity delivered to the room.
A return air grille is significantly undersized. What is the most likely symptom in the living space?
Answer: Negative pressure in the room causing doors to slam shut or stick
An undersized return grille restricts airflow back to the air handler, creating negative pressure in the served space and causing pressure-related door and draft problems.
What is the purpose of a turning vane installed inside an HVAC elbow?
Answer: Guide airflow around the bend to reduce turbulence and pressure drop
Turning vanes inside elbows redirect airflow smoothly around the bend, reducing turbulence and cutting pressure drop compared to a plain 90° elbow.
In a commercial VAV system, when zone cooling demand drops to minimum, the VAV box may switch to reheat mode. What is the energy concern with this operation?
Answer: Reheating previously cooled air wastes both cooling and heating energy simultaneously
Reheat systems cool air centrally and then heat it locally at the VAV box, consuming both cooling energy (chiller) and heating energy (boiler or electric coil) at the same time — an inherently wasteful process.
What is a 'return air plenum bypass' problem and why is it a concern?
Answer: Conditioned supply air short-circuits back into the return without serving the space
A bypass problem occurs when supply air re-enters the return without conditioning the space (short-circuiting), reducing effective airflow delivery and system capacity.
Which SMACNA standard specifically governs the construction and installation of HVAC duct systems in North America?
Answer: SMACNA HVAC Duct Construction Standards – Metal and Flexible
The SMACNA HVAC Duct Construction Standards – Metal and Flexible is the primary industry reference for duct construction, sealing classes, reinforcement, and pressure ratings in North America.