well I know forced air is gonna move the air more, but Ive had them on job sites for 10 yrs.. they're loud, and the heat goes away pretty quick, but they do heat up quick.. Convections dont use nearly as much and seem to be better for a constant gradual heat..
I cant do Kerosene/Diesel .. If Im in the garage for a few hrs, the last thing I want is burning eyes..
I would have got a wall mounted Direct vent / direct propane , but the ground is frozen and I dont feel like stubbing in another line.. I installed the boiler on the 20x24 side of the garage last yr... Dont ask me why I didnt do the entire slab.. Cuz I have no idea...
Either way , the "garage/car " part of the garage will hold heat well as I blew about 18" of cellulose in the trusses, and R19 in the walls, which are sheetrocked..
So I just need something small anyways.. Honestly a 20 lb tank would last me 1/2 the winter.. ( which is usually about 5*-15* avg , and -50 below @ extremes )