quote; I am required to put HVAC register in this room.
Usually, ABSOLUTELY NOT permitted, because that could allow carbon monoxide from a car engine to enter and circulate through the house. Many people have gotten ill, or died, when a car was idling in the garage while the exhaust gases are circulating through the house, because someone wanted a "warm garage". But if you do insist, you have to jump through a lot of hoops to do it, because it would have to have a fire damper in it with a fusible link which activates it in the event of a fire. Your installation would have to be approved by your local fire inspector before AND after it is installed.