If you brew with gas in the garage, you need to vent...for safety's sake. Do you have a window and a fan...? You would probably need to crack the garage door open to get it working right. Like a summer time vent system. Put the burner near the window forcing the exhaust out. That sounds like a logical solution. Unless you want to just leave the garage door open. And fire it up near the open door... That could work too, just don't want exhaust getting sucked into the house.
I brew outside on the back porch all year round. More moderate winter temps than some places in New York (only occasional snow in Oregon's Willamette Valley). Have a system where I set up and break down for each brew as well. Covered area but can get some wind...and can be a little cold, but am a sliding glass door away from the dining room and kitchen.
Works well for me, doing it outside. Pretty quick, the setup and break down. And much safer than trying to deal with exhaust of brewing with gas in a garage. (Unless the garage door is open).
EDIT: Why only brew in the winter?