I have a 36k unit and a 1700 square foot shop. This winter it was about 25 degrees in my shop and I turned the heat on the night before I wanted to work. The unit got my shop to about 50 degrees. Workable, but chilly. I'm going to supplement it with a large wall heater for next winter.
The 36k unit is the largest one they make. In hind sight I probably should have just put a couple or large wall heaters in instead. I don't really have a problem tolerating the heat in the summer so I probably won't use the AC portion of it, its' just the 20 degree days in winter where my fingers just don't work very well that I need heat for.
If your going to heat just half of your shop it should work for it, but trying to heat the entire 1900 square feet it just won't be near enough.