Garage Heat
The problem with any nonvented combustion based heating source (Kerosene convection heaters Kero, LPG, or Nat gas : Bullet heater Kero, LPG, or Nat gas) All of the products of combustion are vented on the inside of the building. CO2, CO, And last but not least H2O. Space heaters will very quickly give you one heck of a condensation and humidity problem.
Go with something like this
http://www.northerntool.com/shop/tools/product_200307959_200307959
Good price right now also.