I grew up with Knipco torpedo heaters huffing on diesel or kerosene smoke in Dad's garage and listening to the woosh of the fan running. I'm not sure what we did wrong but burning diesel always put a thick stank in the garage and even though pump kersonse at the gas station was twice the price not having the stench or smoke haze was worth it. After a few years he got a propane 'flaming sun' heater as a primary heater and it wasn't as loud or stinky but no fan so less direct heat. Tradeoff that I was OK with. Bump the torpedo heater and the flaming sun about 2 hours before you go into the garage and turn off the torpedo when it was comfortable. Granted this is MN/ND so 0-10F outdoor temps was common.
I never knew what I was missing until I worked in my buddies garage had a natural gas vented heater and swore I would get one when I got the chance.
I just got my nat gas heater installed and it's not that much work, really nothing overly complex. It seemed daunting at first but after doing it there really isn't anything crazy. About $600 total and it's really not that complicated. Biggest part is reading all the codes to do it 'legal' and pulling the permits but my wife did that for me lol. The heater was $350, vent supplies were $100, gas piping was $75 and another $75 for wire, thermostat, breaker and random screws and hardware.
Only thing to know is if you vent horizontal it has to be stainless cat III tube which is $$$ and the exhaust has to be 4ft away from any door, window, or vent in the soffit. I ran B vent (double wall mild steel) and you can run it vertical or down to 45 degrees and it just has to dump 3ft above the roof.
Just needs 120v power, 1/2 gas line (which tapping into the gas line in the house is as easy as turning the valve off at the meter and screwing some black pipe back together), a thermostat and vent.
For those in the frigid north it's a good call!