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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

  1. What is 'total external static pressure' (TESP) in an HVAC system?

    Answer: Combined pressure drop across all external components the blower must overcome

    TESP is the sum of all static pressure drops external to the air handler — including ductwork, filters, coils, and grilles — that the blower must overcome to move air.

  2. A duct system has a design static pressure of 0.08 in. w.g. per 100 feet. What design method is being used?

    Answer: Equal friction method

    The equal friction method designs all duct sections to have the same friction rate (pressure drop per 100 feet), making it straightforward to size ducts from tables.

  3. Fire dampers are required by code to be installed where ducts:

    Answer: Penetrate fire-rated walls or floor-ceiling assemblies

    Fire dampers must be installed wherever ducts penetrate fire-rated construction (walls, floors, ceilings) to prevent fire and smoke from spreading through the duct system.

  4. What is the function of a duct sound attenuator (silencer)?

    Answer: Absorb sound energy to reduce noise transmitted through ductwork

    Sound attenuators contain sound-absorbing material (typically fiberglass) that dissipates acoustical energy from fan and airflow noise before it reaches occupied spaces.

  5. In a duct system, what causes the 'stack effect' to influence duct airflow in tall buildings?

    Answer: Temperature difference between inside and outside air creating buoyancy-driven pressure differences

    The stack effect occurs when indoor-outdoor temperature differences create buoyancy forces that drive air up or down through vertical shafts, affecting duct pressure and airflow distribution.

  6. A technician measures 350 CFM at a supply register designed for 400 CFM. After checking the duct system, they find a collapsed section of flex duct. What is the most likely effect on system static pressure?

    Answer: Static pressure increases upstream of the restriction

    A restriction (collapsed flex duct) increases resistance, causing static pressure to build up upstream of the blockage while reducing airflow downstream.

  7. What is the primary advantage of a radial duct system over an extended plenum system?

    Answer: Each branch run is roughly equal length, improving airflow balance

    In a radial (spider) system, individual ducts run directly from a central plenum to each register, creating equal-length runs that naturally balance airflow without extensive damper adjustment.