hello, First time keeper. I have 15 javas around 4 months old. They are noted to be "cold hardy". I live in northern Illinois, where the winter is usally in the 20's down to -20f at times. How warm should the coop be? I've never found a solid answer. Everything says to heat until they stop huddling. I'm looking for a temperature range. At the moment I have an automatic switch to turn the heat light on at 35 and off at 45. Good enough? I know I wouldn't like that temperature range! Thanks!