In ,
spewed forth:
I have a 2-1/2 car garage I would like to heat.

I garage already has a NG line and a chimney.

Any suggestions on brand and type of heater?

You don't say what part of the country you live in, but I've been using an
old Dearborn heater in my shop for years and would highly recommend them.
The newer ones even have a thermostat on them
http://www.dearbornheater.com/
the one pictured is similiar to the one I have. There is no need to vent
them and they'll keep it toasty.
they are very efficient and the unit never gets hot. Hell, I've got
magazines and a fax machine sitting on top of mine