Maybe I'm a bit over-cautious, but please be careful!
If you have the area tightly sealed, you might be able to get a high concentration of CO2 or H2S or something else nasty and dangerous in your hot house from the fermentation. Here's a reference for agriculture workers, but the same concepts probably apply to your much smaller operation (you can probably ignore the "buried in grain" hazard unless you really make a lot of your own bonsai soil):
http://www.cdc.gov/nasd/docs/d00080...36/d000836.html
The problem with a room full of gas is that the early symptoms, especially confusion, prevent people from figuring out that they're in trouble, and then they pass out (remember the airline lecture, "put on your own mask before helping your children with theirs"). Once they pass out, they lay on the floor breathing more gas until they stop or somebody rescues them. I don't know about you, but my wife probably wouldn't come looking for me until at least dinnertime, if at all.
I don't know about the flammability issue (methane?), but smoking a fat Cuban while pruning your trees in your stinky hot house might also be a bad idea.
Yeah, I'm really no fun at all.
Again, maybe it would never happen, but it might be worth letting the place air out for a little while before you venture in, although that might lose you some of your hard-earned heat. On the other hand, it would get rid of much of the stink too.
Be safe!
-Jason.