My chickens are the same age as yours. Where I am at it's already been down to the single digits at night, we've had 50mph + winds, and we've had snow on several occasions. I have not heated my coop. I have half inch foam insulation in the roof only, so I wouldn't say my coop is well insulated by any means, just plywood walls and floor. My girls have been fine. They come out every day. If they don't like the weather they go back inside for awhile after they eat and drink and will reemerge after it warms up a bit in the afternoon. Generally the weather gets colder for increasing lengths of time as we get further into winter. This gradual weather change allows our chickens to acclimate and get used to the cold. As long as they have somewhere to escape the elements, they are their own little space heaters. I have noticed at night the girls will be roosting so they are crouched down on their feet and usually the smallest are sandwiched between the largest birds. I hope this helps you feel better about leaving your chickens out in the cold. I too have been skeptical, and concerned friends keep asking what I will do with my chickens in winter, but honestly, now that the bad weather is here, the girls have proven to me that they will be fine and I have worried over nothing.