I was talking to my dad about heating my shop. He was saying, as has been said here already, that the infrared tubes are the best. But they aren't cheap. He said the panel type, infrared, radiant heaters would be the next best choice. Like this one Summit Carries
http://www.summitracing.com/parts/mrh-mh40ng
He has a smaller one in his garage, but I've never really used it, because he has a shop out back I did everything in in high school. He said a 100,000 btu should heat my shop, or a couple smaller ones.