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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 ASHRAE standard primarily governs acceptable ventilation rates and duct design for commercial HVAC systems?

    Answer: ASHRAE 62.1

    ASHRAE 62.1 specifies minimum ventilation rates and indoor air quality requirements, including duct design criteria, for commercial buildings.

  2. A technician notices supply air temperature drops 8°F between the air handler and a distant register. What is the most likely cause?

    Answer: Inadequate duct insulation allowing heat gain or loss

    Significant temperature drop along supply ducts typically indicates insufficient insulation allowing heat transfer between the duct and surrounding unconditioned space.

  3. What is the recommended maximum air velocity in a residential supply trunk duct to minimize noise?

    Answer: 900 FPM

    Residential supply trunk ducts are typically designed for 700–900 FPM to balance efficiency with acceptable noise levels; 900 FPM is a common upper limit.

  4. When installing flexible duct, what is the maximum sag allowed per SMACNA guidelines between supports?

    Answer: 1.5 inches per foot of length

    SMACNA recommends flex duct supports no more than 5 feet apart, with no more than 1.5 inches of sag per foot of unsupported duct span.

  5. A VAV (Variable Air Volume) box modulates airflow by:

    Answer: Adjusting a damper to control CFM to the zone

    A VAV box uses a motorized damper to throttle airflow to the zone, maintaining zone temperature while the central AHU runs at constant temperature.

  6. Which duct material is most resistant to moisture and best suited for use in humid crawlspaces?

    Answer: Galvanized sheet metal

    Galvanized sheet metal resists corrosion and moisture far better than fiberglass-lined products, which can grow mold in persistently humid crawlspaces.

  7. What is the purpose of a duct balancing damper installed near a branch takeoff?

    Answer: Allow manual adjustment of airflow to individual zones or rooms

    Balancing dampers at branch takeoffs allow technicians to throttle airflow to individual rooms, balancing the system so each zone receives the designed CFM.