80f is a long way from 100f. 80f is inadequate. All things being equal, sure, an open room should work. That’s said, in a room without a fan would develope a thermocline, a layering based on temperature thresholds. 100f up high might be 75f down low, so if you have no fan circulation, you’d need to perfectly position the egs where they are at the ideal temp, ideally using a laser temp gun to monitor the precise temp for the eggs. A mother hen precisely, within a degree or so, manages the temp by adjusting the quills of her feathers to retain or release heat.