Do It Yourself: Heating Duct Installation
Proper ductwork is essential to efficient heating and cooling in a house. Ducts normally are installed during construction or when a new heating/cooling unit is installed. Often the vendor of the unit will install the ducts -- some won't give a warranty unless it does that work -- but a homeowner can install ductwork with some planning and effort. It requires no special tools but some help will be needed, especially if the house is large or has two stories. It's easiest if there is basement access. Does this Spark an idea?
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Things You'll Need
- Tape measure
- House floor plan
- Flexible duct
- Tin snips
- Metal duct hangers and nails or screws
- Hammer or screw gun
- Heat-resistant tape
Instructions
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1
Mark the location of the heating/cooling unit on a floor plan of the house. Note locations for every supply vent to distribute conditioned air; these should all be on outside walls. Draw a plan for return ducts, to take "used" air back to the unit; ideally there will be one in each room, near a floor on a inside wall, but many houses have only one of two large returns. Locate returns in a hallway or other natural point for air flow if one can't be put in every room.
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2
Draw a detailed plan of ductwork routing, both supply and return, which must use separate ducts. Use a "trunk and branch" system, with a large main supply duct going from the unit through the house, with branches to individual rooms or vents. Make the return system similar, if possible; otherwise locate returns in some central area which will draw air from all spaces. Avoid any sharp bends and obstacles like electrical boxes, hot water lines or other utilities.
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3
Install the supply system first, starting at the unit with flexible duct. Run ducts through a basement or crawl space if possible, through an attic if underneath access is impossible. Avoid any areas subject to dampness. Fasten ducts to floor joists at least every 6 feet, if working underneath, with metal straps that go around the duct and nail or screw to the joist on either side. Lay ducts over ceiling joists in an attic and fasten to joists with metal straps; fewer fasteners are needed in an attic, but some must be used to keep ductwork from moving if wind gets into the attic.
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Place the trunk duct first. Add branches by cutting into the trunk duct with tin snips, using a metal connector and sealing the joint with heat-resistant tape. Metal connectors slip inside both duct elements in a T shape. Connect each branch duct to its vent, which will have a round opening to match the duct. Secure with sheet metal screws and heat-resistant tape. Vents are rectangular or square in the floor, but have a round connection at the bottom. Use straight metal connectors where more than one length of duct is required. Slip both ducts over the connector and seal the seams with tape.
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Install the return system, starting at each opening in the house and running back to the unit. Avoid bends and make runs as straight as possible. Connect the return duct at the opening to a frame which will hold an air filter. The frame screws to wall studs; ducts fasten to circular openings at the back or bottom of the return frame. Secure ducts with heat-resistant tape.
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Connect main supply and return ducts to the unit. Typically, each side will have a metal tube which comes through the wall into the house. Fasten duct ends to the connector with sheet metal screws and seal with heat-resistant tape. Test the ductwork by forcing the unit to turn on, either with a manual switch or by setting the thermostat so the unit will activate; examine all seams for tightness. If a seam is flexing or bubbling when air goes through, secure it with tape until it is air tight.
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Tips & Warnings
Don't use duct tape. Despite its name, it is not heat-resistant and the adhesive will lose its strength over time.
References
- Photo Credit Jupiterimages/Comstock/Getty Images
