I was asked to repost this thread, but with the new system it is gone, so I will do it as an article. I am not a biologist, or a specialist of any kind, and I am still learning after all these years.
First, let's do some history, chickens have been here way before us, and have never needed us to count on for surviving as a species. They have adapted to nearly every climate. We have domesticated and made breeds to suit our needs.
In this day and age we are spoiling them as we have our kids, who no longer play outside or are made to do chores, learn basic things like cooking, equipment maintenance and so on, and even homework in some homes, the parents do it for them while the child plays video games. I have personally seen all of this, and my ex, was guilty of the homework thing. Of course the child suffers for it in the long run.
Chickens are very hardy, and will adapt to the environment they have lived in. Cold is not an issue for them. Think about it, a 140 years ago or so, folks were definitely not heating barns, coops or any animal structure for that matter, as it would have burnt the places down. Even today, people don't have or use electricity in some cultures and those living off grid, so they don't heat the coops. We do this because we don't want them cold it makes us feel good.
Here is 50 years of real life experience, not what I think but how I was raised and what I do now with my own flock. NO HEAT IN MY COOPS, rabbits, quail, and ducks, nor outside dogs for that matter. I do use a 40 watt bulb on a timer in the winter to keep the light hours up for laying, I get eggs every day of the year. I currently have 6 hens that are not allowed in the coop at night do to the pecking order (that will be another article). Since I free range, they do use the nest boxes for egg laying, but that's it. Three of these hens were hatched by the current flock, the other 3 came over my 5 foot fence to get away from 2 dog attacks at my neighbors. They have been there since winter and the neighbor doesn't think they would stay home now, so I have them for good. One is a little Polish hen. These last three roost 15 feet up in a pine tree every night. The other three roost on the 7 foot fence surrounding my enclosed chicken yard, I had to put roosts there to keep them from breaking down the wire. Even they (all sisters) have a particular place on these roosts. Not in your spot, you get kicked off and start over. These six hens, have been in rain, snow, an ice storm and 0 or below temperatures. I even made a set up for them outside of the main chicken area and they will not roost in it. They are very hardy, and I personally believe are stronger do to living in these conditions. In the past I have had birds survive -20 deg. with a -70 windchill, a 30 day run of 0 or below temps with no ill effects.
What I do for them is this, food, and water twice a day (do to it being frozen), and 2x4 roosts, flat side up so they can cover their feet when roosting. Even the outside ones don't have that luxury, and have lost no toes or anything else in those temps. Also as a note, a guy I work with has a grandmother with many chickens, a local small town supplier of eggs and meat, who uses no housing at all. They all roost in trees or brush and she collects the eggs from where the hens have chosen to lay them. Now that is roughing it, but, keeps her in shape.
This is just fact and experience I am giving you. Do what you will and what makes you feel good. Spoil them like kids if you wish. But they sure don't require it. Enjoy them and the bounty they give you every day.