If the room temperature is hotter than the desired incubator temperature it will get too hot. If you have to keep your incubator in a room that is consistantly above 90 degrees, you can use a peltier elecrothermal chip on a heat sink and use a Herpstat to cool the eggs down to 90 degrees, instead of using a heat source to heat the eggs to 90. Depending on the ambient temperature and the size of the incubator, it might requre a lot of thermal units to do the job, so finding a cooler area might be the easiest option.