just got chickens around march of this year, so this will be the first winter for the chickens. my coop is 4' by 6' and 2 levels on it. there are no drafts in it, but not insulated, but about as warm and airtight as it can get for being made out of wood. I have a window that I like to leave open a little bit for air ventilation. I have 4 Columbian rock's, 5 regular brown chickens, and 1 rooster. not to worried about the rooster or Columbian's seeing as they sleep outside in a tree every night.. but when it does get colder is there anything I should do to help improve the heat in the coop? I sometimes use a heat lamp on cold nights but don't really want to use it every night through the winter... for bedding I use shavings and then straw on top.. any tips on keeping it warm? or is that good enough?