StadiumDetail said:I tried the propane heaters in my shop last year, and although they worked fast and well the fumes certainly gave me a headache. I have heard the opposite of what ten39 said about kerosene, that it burns away cleaner than propane with little to no fumes and it is certainly cheaper to run. I still think the torpedo heaters is your best route to take, but research it a bit because there seem to be conflicting reports.
Also consider a combination of everything mentioned in this thread. Start at the local coin-op to blast out under your car and the bulk of the dirt, drive the car home to park in the garage and leave it for 30min with the propane/kerosene heater running, then do your ONR wash. This is a great way to get the best possible wash at the cheapest price while staying reasonably confortable.
EDIT: Looked quickly around the web and it seems kerosene and propane boht have the same problem, carbon monoxide. One doesn't seem to be any worse than the other, but every site mentioned a CO detector should be installed when in use. That really isn't a bad idea if you use the torpedo heater.
Most guys crack a door or window when using either a propane or kerosene heater for the carbon monoxide issue, and the instructions recommend such. The venting needed is not much though. One of the 50K BTU units I'm looking at only recommends two 1/4 cu. ft. sized "vents" in your workspace.
My personal experience is with radiant and forced air kerosene heaters, and they're far from clean burning. They tend to kick out a smoke cloud on startup and shutdown, and they smell terrible even in full power use. No matter the level of efficient combustion, kerosene/diesel/jet fuel just puts off some nasty fumes.
If propane is giving you a headache, it's CO, not fumes. Remember propane is an odorless gas both in static form, and in combustion. The "smell" is just put in there at the production stage for safety issues.