The present disclosure includes air spinners for use in duct burners, and duct burners and duct burner kits including a plurality of air spinners. Air spinners may include a plurality of blades extending radially outward from a fuel path and configured to impart rotation to air flowing between the blades, where the air spinner is configured to be coupled to a fuel runner of a duct burner such that the air spinner encircles a fuel outlet of the fuel runner with the axis of the fuel path extending at a non-parallel angle from an axis of the fuel runner. Duct burners can comprise a plurality of air spinners coupled to a plurality of fuel runners. Duct burner kits can comprise a plurality of air spinners configured to be coupled (e.g., without welding) to a plurality of fuel runners.