Full System Installation: Planning, Execution, and Inspection

Full System Installation: Planning, Execution, and Inspection

Installing a complete duct system is the capstone skill of this course. You will move through three distinct phases—planning, execution, and inspection—and each phase builds directly on the ones before it. A mistake on paper is easy to fix; a mistake in sheet metal behind a finished ceiling is not.

Phase 1: Planning the Layout

Before a single screw is driven, your team draws a duct layout. Start with the floor plan of the mock structure and locate the air-handling unit (AHU) or furnace. From there you will route the main trunk duct—the largest duct in the system—toward the conditioned spaces, then branch off to each supply register. Size your trunk and branches based on the airflow (CFM) required at each outlet; your instructor will provide the design CFM values for the mock structure. Register and grille locations must be marked on the drawing with dimensions from walls.

Return air is as important as supply air. Identify where return grilles will be placed so that air can travel back to the AHU without dead-end pressure buildup. A balanced system—roughly equal supply and return—prevents room pressurization problems, door gaps, and noise. Submit your completed drawing and get instructor sign-off before touching any material.

Phase 2: Installing the Trunk and Branches

Work from the AHU outward. Set the trunk first, then add branches, then hang registers and grilles last.

Supporting ductwork correctly keeps the system from sagging, vibrating, and pulling apart at joints. Support sheet-metal trunk ducts at intervals no greater than what the applicable standard and your instructor's checklist require—typically every 10 feet or closer for larger duct. Flexible duct requires support at shorter intervals to prevent sag; consult the manufacturer's instructions and your checklist. Excessive sag in flex duct increases friction, cuts airflow, and can cause the inner liner to collapse.

Bend radius for flexible duct is critical. The centerline bend radius must be at least equal to the duct diameter; tighter bends pinch the liner and can reduce airflow dramatically. A 6-inch flex duct, for example, needs at least a 6-inch centerline radius at any bend.

Sealing every joint is not optional. Apply mastic compound generously over every connection—trunk-to-trunk, branch take-off, flex-to-collar, and register boot—then embed fiberglass mesh tape into the wet mastic. Mastic alone without mesh can crack over time; mesh alone without mastic allows air leakage. Pressure-sensitive foil tape that is UL 181-rated may be used per local code in addition to mastic, but it does not replace mastic on critical joints in attic or crawlspace simulations. Never use standard cloth duct tape on ductwork; it fails quickly under heat and humidity.

Insulating duct runs in unconditioned spaces prevents condensation and heat gain or loss. Wrap exposed sheet-metal runs with duct wrap insulation and secure seams with the appropriate tape. Flexible duct sold for unconditioned spaces already includes an insulating jacket; confirm the R-value meets local energy code requirements before installation.

Manual dampers placed in branch takeoffs allow you to balance the system after installation. Install a damper in each branch, verify it moves freely, and leave it fully open for the inspection; balancing is done after the inspection is complete.

Safety on the Job

Sheet metal edges are razor-sharp. Wear cut-resistant gloves whenever you handle sheet-metal components, and use snips—not your bare hands—to bend or adjust edges. Safety glasses are required during all cutting and drilling operations. When working overhead, be aware of who is below you; a loose section of trunk duct falling from head height is a serious struck-by hazard. Secure every duct section in its final support before moving on. If you need to use a ladder, follow three-points-of-contact rules and have a partner foot the ladder.

Duct board and insulation fibers are skin and respiratory irritants. Wear gloves and a minimum N95 respirator when cutting duct board or handling loose insulation, and keep the work area ventilated.

Phase 3: Peer and Instructor Inspection

Once installation is complete, your team switches to inspector mode. Using the program's 20-item duct installation checklist, you will audit another team's work item by item. Mark each item Pass or Fail with a note explaining any failure. Be thorough—this is practice for the fieldwork you will perform on real jobs.

After the peer inspection, your instructor conducts the final inspection using the same checklist. To pass, you must score at least 18 out of 20 items, and no safety-critical item may be marked Fail. Safety-critical items include: unsecured duct sections at or above head height, unmasticized joints in the attic simulation zone, and exposed sharp edges on installed components. Any failed item must be corrected immediately and re-inspected before the lesson is signed off. Document all corrections in your lab-log notebook with the date, item number, and description of the fix.

Documenting Your Work

Your lab-log entries for this lesson must include: the as-built duct drawing, a list of materials used, a record of peer inspection findings, correction notes for any re-work, and your instructor's final sign-off. These records mirror the documentation habits expected on commercial jobs and are evidence of competency for NCCER portfolio requirements.