I came off my gas water heater and mounted mine to wall. View attachment 331932
These ventless old gas heaters are what I have too. Works great and I got mine for free from someone renovating a house. Just poke a hole in the wall or mount it to a piece of plywood tied to the wall. Warms the whole 2 car garage up to 50 degrees in about 1 hour at 10 degree outside.
This is in addition to my regular electric garage heater I keep running anytime it's below freezing in there. I have exposed pipes (botched project I will fix someday) and can't have it get below freezing in there.
Those ceiling mounted heaters would be nice. I just probably wouldn't use it enough to justify the investment to the wife.