depends on if the bater is still air or has a fan. For still air,the temps should be around 101, but would probably do o.k. anywhere from 100-102. For fans,the optimum is 99.5, but you'd probably do o.k. anywhere from 99-100. It's better to be on the cool side,it just may take the eggs a little longer to hatch. If the temps chnage for just a little while,most of the time the eggs will be fine. I had a broody set this past Summer when the temps were anywhere from 102-106 for 2 weeks straight(even at night). She hatched 2 chicks out of 8.