There have been many many discussions here regarding the different methods of heating a shop.  We've had an overhead LP furnace in our first shop, a big forced air wood stove augmented with used oil in the quonset we used when we outgrew it, and we have an oil fired hot water furnace in a small detached mechanical room heating water to the floor of our current shop, so I've been around several different choices. 

Now, lets think about an incident which is not all that uncommon in a shop.  There are lots of liquids in a shop.  Sometimes they get spilled.  Sometimes they are flammable things.  Suppose, for instance, that you are removing the fuel tank from a vehicle for a repair.  Suppose the vehicle runs on a volatile fuel, gasoline for instance.  Suppose for some reason an amount of said fuel remains in said tank.  Suppose the fuel spills.  If that were to happen, which would you prefer the walls of the shop you were working in to be made of, steel, or wood?   What method of heating would you prefer to have keeping the shop you were working in warm at that instant?  Where would you prefer for that heater to be located?

I know two shops where virtually this exact scenario has happened.  

One of them has been replaced. 

The other one had the doors opened for a few minutes while the fuel evaporated.   

One was all steel, and was heated by floor heat with an external boiler. 

The other was built of wood, and heated by a forced air furnace. 

Just a little food for thought.