With my hatching eggs coming later this week, I've got the incubator prewarming. I learned last year that it does take a little while to reach temperature, and stabilize at the recommended 99.5 degrees Fahrenheit. The manufacturer directions say 6-8 hours, but I found that it took about 24-ish to really get consistent. So, it's plugged in and waiting for those eggies to arrive in plenty of time.
One thing that does impair my set-up is that the only place for it is in my "spare room", which is really a glorified hallway. The bathroom is off it, and runs rather cool, and then the other three entrances all face the doors to the house: one in the kitchen, and one to the back door. After muttering and dealing with a room that has temperature fluctuations, I've come up with a relatively ingenious plan.
Simple double-folded sheets, hung from tension rods and spring clip rings across the doorways. Inside the room, I'll be turning on the electric baseboard heater (which I never use except for this purpose) to keep the temperature in the contained area around 65-70 degrees. While I can't do much about the stairwell rising air to the loft area, I think by covering up the doors and placing a little heater in the room should help a bit. Ideally, if the room is around 70, the incubator should have an easier time maintaining and keeping the desired temperature...and I should, in turn, get a better hatch rate with healthy little chicks.