adding a supply vent

[vdotmatrix]

I have sheet metal ductwork in our home running lengthwise for HVAC.

The trunk is covered but accessable behind drywall.

When the dew point gets to be above 74, i have a rain forrest in my garage.

SO, I was thinking, cut a hole to access the ductwork and tie into it.

What vent size should I put put in?

I used to work HVAC a zillion years ago.

But we used ductboard. We would cut a hole in the duct, tape in some FLEX, put in a boot of pre-determined vent size and tape the flex to the boot done!

This will be like a flush mount cuz the duckwork runs right next to the drywall.

can anyone tell me what to do. The Garage is roughly 12 x25. We have a new clopay door and new triple pane windows opened.