Don't keep it in a heated room, that really will kill it. Dig a hole, shove it in and bury the roots. Then it'll be fine till you're ready to plant it out properly. If you can't do that, put it somewhere cool, preferably where the roots are going to be protected from frost, as I'm not sure what, if anything, it does to them. Keep the roots damp, and don't leave it too long. Get it heeled in on the next mild day, if not sooner.