Garage Heater

Since we know have the house stove taken care of with lots of help from this forum, it is time to tackle the garage.

The garage is attached to the house, is approx 900 sguare feet, is insulated with R-19 ceiling and R-11 walls and has Raynors best insulated steel doors. It only gets below 32 when the outside temp is -20 or lower for days on end. I would like garage heat (NG) for car work, and just the general it is nice to have a 50 degree car to get into rather than a 20 degree car. Any brands to stay away from in garage heaters, how big do I need to go, is used realistic, any brands I should consider, etc. Thanks for the insights all the response was very helpfull for the house stove, I hope I can get the same type of usefull info for the garage.