Well now that one is a dang really a dang good question, and sitting here trying not to be a SMART------ how about a heating pad on low, or those 72 hour warmers, or putting the boody chicken and her laying box/nest in more sunny heated area of your resident, another suggestion I might add is the kind of bedding in the nest, I was using pine straw, and changed mined several times experimenting the type of nexting box also plays a part in heat control, I put a quarter inch piece of ply wood in the bottom of all mine and there is a wheat field next to my home, when they cut the wheat I went and raked up the cuttings left and filled my nesting boxes thick with these cuttings, and this works better for me and you can actually feel the heat in the nest when you slide your hand in under the chicken??? I was only first of all sharing my experience with me trying to impove my ratio of females and males in the hatching cycle--stage and give you an idea that I use, but nevertheless, BEST WISHES and hope you have a HAPPY 4th.