Removing old sheet metal air duct from an attic

[Stephen Tashiro]

I need to remove an old sheet metal air duct about 20 ft long that's over the ceiling of a hallway. I can get to it by working in the attic, but I'll have to cut it into pieces to get it out from under the ceiling joists. An alternative would be to tear out the ceiling of the hallway, including the 2x4's under the duct and take the duct out in one piece. I suppose that would make sense if the duct is replaced by a new sheet metal duct. However, from a DIY perspective, it would be simpler to replace the old duct by several flexible ducts.

What's the best tool and technique to use if I cut up the old duct? (A large section of the bottom of the duct rusted away from being under the swamp cooler. Cutting up the rest of it will require the same effort as cutting new sheet metal.)

[Lee Schierer]

I need to remove an old sheet metal air duct about 20 ft long that's over the ceiling of a hallway. I can get to it by working in the attic, but I'll have to cut it into pieces to get it out from under the ceiling joists. An alternative would be to tear out the ceiling of the hallway, including the 2x4's under the duct and take the duct out in one piece. I suppose that would make sense if the duct is replaced by a new sheet metal duct. However, from a DIY perspective, it would be simpler to replace the old duct by several flexible ducts.

What's the best tool and technique to use if I cut up the old duct? (A large section of the bottom of the duct rusted away from being under the swamp cooler. Cutting up the rest of it will require the same effort as cutting new sheet metal.)

I would use and oscillating multitool with a metal cutting blade. Be sure to wear ear protection and a dust mask. A rotary tool with a cut off wheel will throw a lot of sparks in an area where they could be dangerous.

[Tom M King]

Multitool (since you probably don't have a battery powed, handheld bandsaw) to start a cut, then tin snips with offset handles (I recommend Milwaukee), and power shears. Some are lined with fiberglass insulation. Can you just replace the part that needs replacing, where it's rusted?

[Matt Day]

I don’t know, not sure I’d want to hear the racket of a multitool cutting sheet metal in an attic for 20’ of cutting. I’d consider something like a metal shear like this one from HF:
https://m.harborfreight.com/14-gauge...ars-62213.html

[Mike Cutler]

Pneumatic shears.
The Tin Knockers at work have some electric shears which are pretty cool.
There is probably a battery powered version available now.

[Brad Chenoweth]

Isn't the duct assembled in sections? Most large ducts are assembled in 5' sections, with drive clips.

[Roger Feeley]

My tool of choice would be a pneumatic nibbler. it runs on your air compressor. Just use a step drill to drill a starter hole and then the thing will go through the metal like butter. Like the multi-tool, it will be noisy but, in my view, a LOT safer.

$28

https://www.harborfreight.com/16-gau...ler-46061.html

[Bruce Wrenn]

I would SKIP the nibbers as they leave a bunch of half moons of metal. I take each section apart at the drives, and then break it down using the electric shears from HF. At each joint, you will have two drives, and two "Pittsburg" locks. Knock the drive off, and the duct slips out of the Pittsburgs.

[John Terefenko]

If it does not have splines which you can take apart, I would knock a hole with a screwdriver and use snips. If there is toxic dust in there you do not want to be spreading that around with electric rotor snips. Also be careful tipping it to get out the hole. I would cover the hole with a large plastic bag and duct tape it. So you do not track through the house. Wear a dust mask.

[Stephen Tashiro]

Isn't the duct assembled in sections? Most large ducts are assembled in 5' sections, with drive clips.

I see only 1 joint in the duct. It appears to consist of two 10-ft sections that are joined. It's 1956 vintage construction.

[Stephen Tashiro]

I donÂ’t know, not sure IÂ’d want to hear the racket of a multitool cutting sheet metal in an attic for 20Â’ of cutting. IÂ’d consider something like a metal shear like this one from HF:
https://m.harborfreight.com/14-gauge...ars-62213.html

I happen to have that particular tool , as well as a similar tool from DeWalt. They work well for cutting flat sheet metal. I don't know a good way to cut around the corner of a square duct with them. The duct is wrapped with a thin (about 1 inch) sheet of fiberglass insulation that must be removed or cut through.

[Bob Glenn]

Let sleeping dogs lay.

[Pat Barry]

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.

[Tom M King]

Cutting the sheet metal wouldn't be bad, but that compressed fiberglass insulation glued to it is the worst of the worst fiberglass to have to deal with.

I'd be looking for one of these types of lining systems: https://www.ductarmor.com/ Just put a patch over anywhere that's rusted all the way through.

[Andrew Fleck]

You can easily cut that sheet metal up with some compound tin snips.