You guys running propane, watch the condensation. I noticed when I was running my propane heater, it created a TON of condensation (a by product of burning propane is water vapor) and it would collect on ALL my tools (including those in a tool box). It works, but if you use it a lot, spray your tools and anything cast (like machine beds/tables) with WD-40 to keep them from rusting.
I made the switch to a permanent, natural gas heater and I keep it on all the time (thermostat stays around 50)...Its SO MUCH BETTER. I realize its a luxury, but I'll never go back to an unheated shop space again. I gladly pay the extra gas charge...my floor is warm, the tools are warm, I don't have condensation issues, no venting issues, etc.