We lost power last night and I had 5 one week old chicks who needed heat. My survival skills kicked in and I found hand warmers that I activated and put into socks and tied off the ends so they couldn't get at it. The hand warmers stayed warm for 8 hours (luckily the poer came back on after a few hours). All chicks sat their little bottoms on a "warm sock" before I left them with a flashlight on top of their brooder box and greeted me with little peeps in the morning.