You're on the right track. Most of those type heaters have bi-metallic type thermostats that spark when they make or break the circuit, just like the spark plug in your car's engine, that ignites the gas vapors in the cylinder. An oil-filled radiator type heater with an electronic thermostat (non-sparking, but does such a thing exist?) would also have no exposed heating element, and might be a good choice, but again, most of the ones I've seen in that price and heat capacity range draw 1500 Watts, which at 120 Volts nominal, eats up 12,5 Amps of a typical 15 amp household circuit. Your garage may have a 20 A circuit, but that still leaves a very slim margin for running power tools, lights, etc.