Alternative to the heater fan?!

Yes, for example. Something like that

Basically, infrared heat is not "scheiße," but it is unsuitable for your garage because it would need to be on for a longer time to have even a small warming effect. Your heater, on the other hand, gives off a lot of heat exactly when you want it. In the house, I find infrared heat very pleasant.

The two contradict that it has to be on for a long time!

With an infrared heater, the purpose is not to heat the room but the objects that are illuminated. In this case, the person working there. You turn on the heater, and as soon as the unit glows and you are being illuminated, it is warm.

For example, a changing table lamp for babies works the same way.