I have used them in an indoor conservatory/spa/pool in my house that I had in Edmonton Canada. I had two and ran them in parralel along the ridge.
They were extremely good and inexpensive to heat and kept toasty a 2,400 sq.ft. area. I had them mounted up high {about 24' } and I needed no other heating except for the pool and spa water heated. Kept the water at 86 F. and I had no issues with the very large windows icing over in even minus 50. I used four ceiling fans originally {Humphrey Bogart type, slow turning } but later I kept them off because I had free flying bids in there. No problems or issues over 8 years I lived there. They are used extensively in warehouses.