if you have never used a bullet heater, rent one before you buy it, and try it out, YOU WILL BE breathless in 30 minutes, and have the door wide open before long, trust me, ive been there, a monoxide detector will go off in 5 to 10 minutes of starting the heater up, thats why you see them on construction sites with open walls and such, the box its in will give a warning not to use it in a closed area., using these heaters is the same as running your car in a closed garage, not the best idea.
any heater that is mounted to the ceiling of the room and is vented, such as gas, oil, or propane should be just fine, but it will cost some coin.