garage heating

When I lived in michigan, I tried propane heaters a few times, they basically spew carbon monoxide, we always got sick when we used these. Ideally you want radiational heat, like an electrical element heater, or the safest, oil filled radiators. They are also the slowest to heat up the space, but they retain heat really well. You can put a small fan on low blowing through the radiator to heat the space a little quicker. I have one on in my garage all the time since I am doing a lot of painting and need to keep the space above 65F. Also, try to avoid opening the main garage door, use a side door if possible.