Ductwork Installation
- 1). Diagram routing for the ductwork using a "trunk and branch" scheme with a main central duct and offshoots to individual vents. Mark all vent locations and plan return ducts, to take "used" air from rooms back to the heating/cooling unit. Try to put one return for every vent. If this is not possible, place large returns in hallways or areas where air will flow from several rooms. Put supply vents on outside walls, returns on inside walls. Measure all runs for specific duct lengths.
- 2). Place ductwork with as many straight runs as possible. Avoid sharp turns or bends. Stay away from electrical fixtures and boxes, hot water pipes or other obstructions. Put ducts between floor joists in a basement or crawl space. In slab construction, put ducts between ceiling joists and in wall cavities. Run ducts in attics, if necessary, with a straight flow up a wall or closet to the attic.
- 3). Secure ducts about every 6 feet. Use gas pipes or cold water pipes for support where possible. Put metal strap braces where no natural support is available, around the duct and nailed or screwed to floor or ceiling joists on both sides. Keep flexduct loose but not sagging and avoid pinching ductwork with straps. In an attic, leave ducts loose over joists, but secure in a few places to prevent ductwork from moving with any wind.
- 4). Use metal connectors to join duct sections, either on straight runs or on branches. Put part of a connector in each element to be joined and secure the seam with heat-resistant tape. Cut ductwork with tin snips as needed; flexduct is formed with wires surrounded by fiberglass insulation and a metallic fabric cover.
- 5). Test the system when all ducts are installed by forcing the unit blower to turn on and checking for leaks. Some units have a manual blower switch, others must be activated by adjusting a thermostat until the blower kicks on. Look for any loose or blowing duct pieces and block any such leaks with heat-resistant tape.
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