An adjustable boot hanger mounting bracket assembly comprising a boot hanger frame portion and a support member portion; the ductwork components, which may include a prefabricated can-boot/mud ring assembly; a pair of boot hanger arms; and a register grille. The boot hanger mounting bracket assembly is formed of a sturdy yet bendable material so that it can be configured and adjusted on-site. Once configured, the assembly is secured to the building structure by a securing a pair of boot hanger arms to the ceiling joists, wall studs, or other support structure. In this way, the boot hanger mounting bracket, through a direct attachment to the ceiling joist or wall stud, provides a positive inexpensive simple and error free way to mount the duct components.