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Home Repair: How to Flatten Basement Air Ducts to Gain Space

Install wider, flatter heating and cooling ducts (you can have them custom made) to increase headroom in your basement, especially when finishing the ceiling.

By the DIY experts of The Family Handyman Magazine

Replace a low-hanging duct

Don't let low-hanging ductwork scuttle your plans for a basement remodel. If the ductwork is in the way, you have three options. You can reroute it or split it into more but smaller ducts. But the least disruptive and easiest way is to replace the low ducts with new ducts that are flatter but wider. In most cases, you can gain several inches of headroom.

Measure the existing ducts that are too low. Sketch out the current duct layout and note the location of each joint. Take the sketch to a professional heating contractor and get a quote for building new, flatter ducts. If the new ducts provide enough headroom, just deliver the old ducts to the contractor to use as a template for the new ones.

To disassemble a duct joint, remove the drive “couplers” (Photo 1). Then install the new duct (Photo 2). Seal all the joints with aluminum duct tape or duct-sealing caulk.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Hammer
    • Spring clamps
    • 4-in-1 screwdriver
    • Drill/driver, cordless
    • Stepladder
    • Pliers
    • Safety glasses

You'll also need leather gloves.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • New thinner ducts
    • Drive couplers
    • S-slips
    • Duct hangers
    • Aluminum duct tape or duct-sealing caulk

Comments from DIY Community Members

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January 23, 11:14 AM [GMT -5]

This is disappointingly lacking in information.

1. It appears that all he is doing is raising the duct, from its original position to just under, maybe even touching, the floor joists. I this this might result in more noise as the ducts bang against the joists as the HVAC system comes on and either heats up or cools off.
2. Although not an exact science, and I'm sure that every installer does the math a little differently, the volume of your ducts should be a function of the size of your furnace and house, and how far and how many runs you have. Altering a main in the basement near the system might negatively impact its performance.

The question is, can I take a duct that is approximately 32 inches wide, or two joist bays, and (let's say) 12 inches deep or high, and make it 64 inches wide and 6 inches deep?
- This might make it really hard to hang a ceiling, but I'd gain 6 inches.

January 15, 11:25 PM [GMT -5]

I was just curious on how shallow these new ducts can be? Ours currently are spanning approx 25 feet in a strait shot.
Any feed back would be appreciated.
Thank You,
The Flemings

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Home Repair: How to Flatten Basement Air Ducts to Gain Space

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