I find the chicks are a better temperature indicator than a thermometer. I know the ideal is to start at something like 85-90 degrees & drop it down 5 degrees each week, and I don't want to steer you wrong. But I stick a desk lamp in one end of the brooder box & watch what the chicks do. If they huddle shivering right under the light I figure it's too cool, if they avoid the lighted area entire it must be too warm. If they act happy & busy, moving about the box on their tiny birdy business it must be just right. I rarely keep a thermometer in the brooder box, the chicks just poop all over it.