How to Install Flex Ducts in New Construction
- 1). Make a layout of the basic duct-work routing, from the unit through the house with branches to all vents. Locate vents on exterior walls, preferably near windows. Plan a return system to collect air from inside the house and return it to the unit. Place returns in every space with a supply vent or in a central hallway or similar location where air flows naturally. Match return ducts to the airflow output of the supply side, so the system is balanced.
- 2). Use "natural" supports such as gas lines or drain pipes to support flexduct in a basement, but don't use these spaces if they crimp or crowd the duct. Fasten ducts in a basement with metal hangers, which go around the duct, and nail to joists on either side. Lay ducts between joists in an attic and fasten in a few places with metal straps to keep ducts from shifting with any air that comes in.
- 3). Run a main supply duct from the unit through the house, as straight as possible. Go through the center of the house in a basement. Go up through a wall cavity from the unit to reach an attic. Run that main duct first. Cut openings in the flexduct with tin snips for branches to individual vents. Connect branches to the main duct with T or Y connectors, which are metal sleeves fitting inside the two ducts and are fastened with heat-resistant tape.
- 4). Attach branches to vents, using the metal connectors on the vents and secure with tape. Run small ducts down wall cavities if vents are located in walls or attach in the attic for ceiling vents. Houses built on concrete slabs usually use ceiling vents except in locations where ducts can be run down through larger openings, such as inside closets or utility rooms.
- 5). Install a filter frame at the opening for a return duct. Fasten the frame to wall studs on either side of the opening, Nail a cross board at the top of the frame opening if necessary; some filter frames require cutting off a stud to make room for the frame.