This is what was in my 30X40 shop when I bought it last fall, it has R13 in the walls and a bunch (unknown) of blown in cellulose in the ceiling, and insulated doors. It did very well last winter even in January when the temps were around 10*. Couldn't find a tag on it, but IFIRC, it pulled 41A when I checked it so it's about 9.8kw. On the very coldest days, it'll run about 20 minutes to get up to 65* then cycle for about 4-5 minutes 4-5 times an hour to keep it there. I'm pretty happy with it. Haven't taken the time to figure what it's costing me, because the increase in the electric bill hasn't been enough to make me do it yet.
EDIT:It was already installed when I bought the place last year. The sticker on the top references an air handler made by York, used in Coleman mobile home furnaces, so I'm guessing the previous owner sourced it used out of a mobile home. Wherever it came from, it works very well and I am happy with it.
I will however be making a wood furnace after I add on to the shop. It will end up being 45' X 50' and I think that's too much for electric heat alone.