Air Conditioning Home Duct Work Installation

Locate all the vents in a house. Put supply vents, which carry conditioned air into the house, on outside walls, preferably near windows. Make return outlets, which capture "used" air from the house and send it back to the unit, either in the same room with supply vents or in some central area, like a hallway, which gets a natural flow of air through the house.

Design the duct pattern in a "trunk and branch" system, with a main supply duct running the length (or width) of the house from the unit to the outer wall, with branches that fork to individual rooms. Use a basement for ducts, if there is one. Otherwise, run duct work through an attic. Putting duct work in an attic will require a large enough wall or other space for a duct from the unit up to the attic. Place individual room vents in a ceiling or at the base of a wall.

Start the duct installation at the supply outlet of the unit, typically a large sheet metal box with a round connecting point to fasten flexduct. Run flexduct under floor joists in a basement or over ceiling joists in an attic. Secure basement duct work at least every six feet with metal strap hangers, which go around the duct and fasten to joists; you can use gas pipes or other supports instead of hangers, but avoid any hot water pipes or other heated elements. Fasten attic ducts in a few places to keep them from blowing around.

Make branches using metal connectors, sleeves which slide inside the openings of each duct. Get connectors that transition from full central duct to smaller room ducts. Cut flexduct where needed with tin snips. Seal all connections and seams with tape recommended by the flexduct supplier. Don't use duct tape, which does not hold well in duct work installations. Connect supply lines to individual vents and secure the connection with tape or as recommended by the manufacturer.

Build return ducts in similar fashion, from the return entry point to the return element on the unit, again a metal box with a round opening. Install a filter system at the return openings, the size and type depending on the number of returns, their size and location. Typically filter openings will be large, from 12 inches by 24 inches to perhaps 30 inches by 30 inches, metal frames that hold filters with covers that lock in place.