Yes,its best to have an outside air intake and exhaust if a gas heater is used in a "working" garage...guy I knew blew up his garage a few winters ago when his riding mower decided to leak a tank of gas onto the floor overnight,and the heater was set at 55 degrees,when it came on,the overhead door blew out into the street!..

...fire caused 10K in damages..
I found it rather strange that the building inspector didn't really seem to care when I told him I wanted to put a wood stove in the quonset garage back in '92 when I built it--he said "Eh,its metal,just keep it elevated up off the floor on cinder blocks,to avoid any fumes getting sucked into it--and dont use it if your going to paint things with a spray gun,and NO gasoline stored in there either"..(I didn't tell him I was going to "work" in there--it was for storage and "hobby" use only!..

)..he was not happy about me putting a 10x10 overhead door on it,he kept asking if I was planning to park an 18 wheeler in it--I said "no,but I would like to be able to back in my pickup with a slide in camper on it if I get one someday"...
He didn't even make me get a permit for the stove,he said as long as we had one for the stoves in the house,that was good enough.

.but if I wanted a propane heater hanging from the ceiling,he said it would have to be vented,and use outside air intake,and inspected..

..