How Old Do Chickens Have To Be To Stay Outside?

Chickens need to have feathers to survive outside in the cold.  My mother kept our chicks in a makeshift incubator in our oven.  The pilot light and an old towel kept the chicks warm. That might sound silly but chicks are covered in soft down that is soon replaced with pin-feathers.  Once these little feathers start to fill out, the chickens can be exposed; The birds will now look like "teenagers".  Adult chickens can survive outside in very cold climates if they can roost and keep out of drafts.  I grew up on a farm and tended our chickens.  We had a chicken coop that was protected with plywood on three sides. However, the fourth side was covered with chicken wire and open to the elements.  Our chickens lived very comfortably as pets for many, many years.  We provided them with lots of hay for insulation and roosting boxes so they did not have to lay on the cold ground.  Like most birds, they feel safer up high.  Coops are important because even though our chickens were "free range" during the day, we always put them in their coop at night.  Foxes and other nocturnal animals will kill them.