Attaching HVAC vents to drywall?

[weatherby460]

For some reason my hvac guy when he installed heating vents did not leave a flap of tin to screw into. Looks like I have to drill into the drywall. These heater vents come with #8 2" screws. Do I just use those screws and the drywall will hold it, or do I need anchors in the drywall? Thanks

 

[The Cobbler]

can you get behind the drywall?
use a pc of plywood as a backer to screw to, no the drywall isn't really a good option, IMO

 

[Jim greengo]

Are they going in the wall or ceiling?

 

[bazar01]

Request them to replace flange-less register with flanges.
Drywall anchors may work on new drywall, but may work loose over time because they will be right on the edge of the drywall opening.