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Thread: Removing old sheet metal air duct from an attic

  1. #16
    Join Date
    Jul 2005
    Location
    Eastern Iowa
    Posts
    751
    Quote Originally Posted by Pat Barry View Post
    If its a gable roof you might he able to take it out through one of the gable end vents. Maybe you cut it to fit or flatten it and bend it so it will fit.
    Never took something like that out of an attic; did have to put in a 2x12x20’ beam.

    Something similar to Pat’s suggestion, but no gable vent.
    $1.79 for a vinyl siding removal tool.
    Pulled a couple of rows of siding, about 5 minutes.
    Cut an opening in the sheathing big enough for the beam.
    Slid it in,
    Screwed a 1/4” backer over the hole
    Glued and screwed the plug back in
    Reinstalled the siding, (another $1.79 tool),

    Seems rectangular ductwork can be pushed almost flat. Even if not, pulling a couple more rows of siding is simple.
    .... just thinking....
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  2. #17
    Join Date
    Apr 2010
    Location
    Berkshire County in Western Ma
    Posts
    200
    I have a dewalt electric shear for sheet metal. I use it to cut up old washers and dryers, microwave oven housings, aluminum and steel. I think they are rated for 18 ga steel. Picked mine up at a pawn shop. With some coaxing, you can cut around a 90 degree bend. Cut away a narrow strip of insulation where you want to make your cut, then go to town. It will leave a long curly strip, not a bunch of small pcs. There is one moving jaw that pivots between 2 stationary jaws. Once you start you can cut all the way across a washing machine in about 15 or 20 seconds.
    Last edited by Tony Pisano; 03-17-2019 at 10:52 PM. Reason: Added info

  3. #18
    Join Date
    Sep 2006
    Location
    Las Cruces, NM
    Posts
    2,037
    The old duct has been removed. The useful tool turned out to be a saber saw with a metal cutting blade. Both a Bosch corded saber saw and a Ryobi cordless saw worked well. Often the saw had to be run in bursts instead of continuously to keep vibrations of the duct from kicking the saw out of the cut. When cutting across the bottom of the duct I tipped the base of the saw away from the duct at an angle to keep the end of the blade from hitting the ceiling below the duct. ( Perhaps a better solution would be to buy a very short blade or to shorten a normal length blade by cutting the end off. )

    I used a spray bottle with water and vinegar in it to mist the fiberglass insulation before I gently pulled it off the duct. The worst incidents of dust happened when a freed section of duct was pulled down from the attic through the opening I cut in the hallway ceiling. Debris from inside the duct spills out. It's best to block the end of the duct before pulling it down or pull it down so it faces sideways.

    My method was to first cut out a rectangular section all the way across the top of the duct, wide enough so I could use the saber saw to make a cut across the bottom of the duct. I used a cordless drill to make holes for starting blind cuts. After making the cut across the bottom, I made cuts down the sides of the duct and used (manual) metal snips to finish the very end of the side cuts where they met the bottom cut. Connections of small ducts to the main duct were pryed apart with a small crowbar.

    My observations on other tools:

    Tools that cut too slow to be useful: Bosch and Porter Cable oscillating mutli-tools. Harbor Freight electric and air powered body saws, manual hack saw.

    Tools that cut well in ideal conditions, but didn't work well on rusty ducts that are free to vibrate: Harbor Freight air nibbler, Harbor Freight and DeWalt electric metal cutting shears. ( I don't understand why the jaws of electric sheet metal cutting shears aren't designed to open wider. Perhaps the type of shear used to cut corrugated metal roofing would work better. Judging from pictures, the jaws on that type of shear seem to have a different design, but I've never used one.)

    A Dremel Saw Max cuts the duct well but shoots a shower of sparks, so I didn't use it in the attic. (Also, the abrasive disks for it don't last long.)

  4. #19
    Join Date
    Sep 2013
    Location
    Wayland, MA
    Posts
    3,656
    Sawzall.

    But then that's how I solve most problems.

    Actually first I'd try taking it apart and bending it flat. But pretty quickly I'd reach for the sawzall to cut it up. Noisy but it will only take a couple minutes-- use ear and eye protection. Snips are fine if you have patience and strong hands. I have neither anymore.

  5. #20
    Join Date
    Feb 2014
    Location
    Lake Gaston, Henrico, NC
    Posts
    8,975
    I know you're glad to have that job behind you!

  6. #21
    I have a obsolete version of this tool, https://www.kett-tool.com/products/KD-400 works great for sheet metal. Mine came from a scrap yard, needed new blades and a power cord and getting rid of the Twistlock® plug.

  7. #22
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,905
    Why vinegar with the water? Good idea to wet the dust done before touching it and shaking it with power tools.
    Bill D

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