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How To Install Air Supply Ducts In A Basement

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If you are a homeowner who plans to install central air, the most common place for sheet metal air ducts is the basement. The air ducts move the cool air to the registers in the home. You could only cool one room without air ducts.

You don't need advanced HVAC skills, but it helps to have some home improvement experience, since it requires working with sharp sheet metal. Here are some tips to install air supply ducts in a basement.

Prepare to Work

For this project, you need:

  • work gloves
  • pencil
  • tape measure
  • duct tape
  • metal snips
  • pipe crimper
  • galvanized hanging straps
  • sheet metal ductwork screws, collars,and elbows
  • sheet metal ductwork

If your system is a combination heat and air unit using the same ducts, contact your local building codes department for information on the best placement for ducts. Some municipalities also require the return air ducts be the same size of bigger as the supply duct. Check your home insurance policy to ensure that your insurance won't be voided.

Map a Route

Draw a floor plan of your basement, noting locations of hot water heater and electrical boxes that need to be bypassed. Choose an output path for the ducts, and choose a return duct path running from the registers back to the main supply.

Don't install return ducts to the basement. This may cause toxic fumes to be released inside. Measure the distance between paths, and buy enough ductwork and hardware.

Install the Ducts

Turn the power to the unit off and the thermostat all the down. Begin installation at the supply unit.

Sheet metal ducts are attached by a crimped end and a non-crimped end. Insert the non-crimped end to the crimped end, and secure it with sheet metal screws. For a tight seal, wrap the connections with a layer of duct tape.

Lay the ductwork, installing it between floor joists and under floor joists where possible. Insert sheet metal elbows when you reach a bend, and trim the ductwork to size with the metal snips. Use the pipe crimper to bend one end of the cut piece.

Support the ducts every three to four feet by hammering them in the center of the hanging strips, which are commonly shaped like a "U." Attach the ducts to vents with sheet metal collars by bending the metal tabs. Install the return ducts in the same manner.

Turn the power back on and raise the thermostat all the way to test the installation. If the unit fails, or you don't trust your skill, contact an HVAC service.


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