Practice Test Geeks(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test
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Airflow and Duct Sizing Flashcards

7 cards from real 313D practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which Manual D concept defines the path through the duct system with the greatest pressure drop?

    Answer: Critical path

    The critical path (or index circuit) is the duct run with the highest total effective length and determines the required system static pressure.

  2. When sizing return air ducts, what minimum free area ratio is typically recommended for return grilles to avoid excessive velocity noise?

    Answer: Return velocity below 500 FPM

    Return air grilles should be sized so face velocity stays below 500 FPM to prevent objectionable noise at occupied locations.

  3. A room requires 200 CFM of supply air. If the supply register has a neck area of 0.2 sq. ft., what is the duct velocity at the register neck?

    Answer: 1000 FPM

    Velocity = CFM / Area = 200 / 0.2 = 1,000 FPM.

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

    Answer: Each branch has equal length for more balanced airflow

    A radial (spider) layout routes individual ducts directly from the air handler plenum to each room, making branch lengths more equal and airflow more balanced.

  5. What does a negative room pressure relative to adjacent spaces indicate about the duct system serving that room?

    Answer: More return air is being removed than supply air is delivered

    If a room is negative relative to adjacent spaces, more air is being exhausted or returned than is being supplied, often due to a missing or undersized return.

  6. When installing duct in a conditioned crawl space, what is the primary installation consideration compared to attic installation?

    Answer: Moisture and condensation management on cold supply ducts

    Cold supply ducts in a humid crawl space can experience condensation on the outer surface, requiring vapor barriers and proper sealing.

  7. Which ASHRAE standard provides guidance on acceptable duct leakage rates for residential HVAC systems?

    Answer: ASHRAE 90.1

    ASHRAE 90.1 (and its residential counterpart 90.2) establishes duct leakage requirements as part of energy efficiency standards.