The present invention relates to duct systems, registers and ductwork components used with floor or ceiling registers employed in warm air heating, ventilating and air conditioning systems, and specifically to improvements for mounting and installing the components of the duct system, including register boots, mud rings and register grilles, in the walls, floors or ceilings of buildings components, mud ring, register grille and wall, floor or ceiling opening, which reduces costs.The invention includes 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 pre-fabricated 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 boot hanger mounting bracket 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.