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

The easiest way to gain valuable headroom

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.

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

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