The best replacement for duct is metal duct.

The best alternatives to duct are rated as following:
★★★★★  metal duct
★★★★  mastitis
★★★  hard duct
★★★  gland
★★  conduit
★★  pipe
★★  pink eye
★★  ductless ac
★★  flex duct
★★  square duct
★★  breast cancer
★★  ductless
★  hard pipe
★  rectangular
★  sac
★  conjunctivitis
★  rigid duct
★  flex
★  rectangular duct
★  flexible duct
  sheet metal
  duct board
  bile duct
  sheet metal duct

Your alternative for duct is not listed? Suggest!
Speaking about duct, one probably shouldn't forget about fan.

Other search terms related to duct and their ratings are:
★★★★★ fan
★★ fan coil units
You have in mind a companion for duct and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of duct in all years. Click on graph for more.
duct
metal duct
mastitis