There were a lot of posts so I just skimmed through most of them, I wish I had time to read every post but alas, I do not
I have one coop, in the barn, open to the outside on one side, 2 sides are solid and one side open to the barn. All wire, no heat. The girls were laying eggs in -13 (minus 13) degrees and if I was off work and could get to them before they froze solid, I could hatch them in the incubator. I made sure they had fresh, clean water daily. They need that particularly in the evening before they go to roost. Increasing the fats in the diet in the fall helped to put a decent coat of fat on them all (I didn't see anything mentioned here about nutrition to prepare for winter). I also give a bit of cracked corn in addition to their routine pellet diet and scraps of course.
Something else I didn't see here was any discussion on breeds. Some breeds handle the winter better and some do better in hotter climates in general. Those breeds with the huge combs are really going to need a good place to keep out of drafts and possibly, a heat source.
all my chickens but one have huge combs, never had a problem with out heat, and I never use the deep litter method, I change out my litter every two weeks. 
never had a problem with frozen combs one time.I believe its the moisture from the poop and not enough ventelation that causes combs to freeze. My Serama's are tiny and originated in Malaysia so enough said, they have a heated building for temps below freezing and outside in warmer times. My Araucana's are those that are super fine in the cold and tolerate the heat okay too.
Fluffy chicken breeds, like cochins etc. I would "guess" that the fluff could help or not with cold. I could see that fluff blowing in a draft or the wind exposing the skin to cold. A really tight feathered breed may have opposite issues. It's a neat thread to read through and probably everyone here is doing the right things for their area and their breeds or else there would be more deaths. I feel that nutrition and planning for their winter months is a good idea. Allowing them adequate rest after molt in the fall, worming them before winter to decrease the stress on the body in the cold, considering a draft free area with plenty of room for them to line up close to roost and stay warmer together, maybe a lower ceiling over the roost to trap some heat. A light source "may" increase stress to their body by making them lay when they might otherwise be resting. speeding the loss of stored fat, etc. If someone is thinking hens are healthy and happy if they are laying all winter, they may find themselves replacing hens much sooner than planned. They can be used up (burned out) pretty quickly if cared for like battery hens.
I know my routine isn't right for every one else but here it is.
My routine here is in the fall is to remove the roosters from any breeding pens about October. I worm them orally with fenbendazole twice, a week before then the day I turn them out. I look for mites/lice but in general, I go ahead and treat with a couple drops of Ivermectin 1% topically. I let them free range (I have dogs to protect them so I am able to pull this one off). The roosters all get along fine (all Araucana's) and they all roost together on the lower beams of a wire pen. They are relieved of their duties, they get to forage, they get fed as well. When they forage, there are many benefits to the rooster. They increase muscle size from being able to run about and fly etc. They eat a lot more bugs that way, there is less stress because no hens. It's like sending a bunch of bachelors to the gym and I feed them very well.
The Araucana hens get their time off too. When the roosters are free ranging, all the hens are cooped together. I briefly drop the quality of feed to help them all go into molt together. Before molt, I worm them, treat for mice/lice as I do the roosters then when they have finished filling the entire coop with feathers, lol, I slowly bring the nutrition back up and take this time to clean out the coops, laying down a layer of powdered lime then bedding. In the winter I use straw and pine shavings to give them something to scratch around but also the heat from the poop in the winter over this bedding is somewhat helpful since it's all dirt flooring. For a while, I give the eggs to the dogs to eat then we eat them when the wormer is out of their system. I don't use any lights and try not to disturb them too much with the outside lights unless I have to. They have fresh water and decent feed along with occasional scraps and greens when I have them. They get a bit of corn in the winter for heat but no other heat source. I want them to "rest" and they need the winter cold and change in feeding patterns to put their bodies into that mode. About Dec to Jan I begin to bring them back into breeding condition with better quality feed, increasing calcium and adding a vitamin A/D/E granules in soft feed. After a couple of weeks to a month, depending on how they look and act, I'll begin sorting them into breeding groups so they can get their pecking order figured out. Then, in go the roosters. Generally 1 or 2 per pen depending on the number of hens and I usually have a few trio's and quads or so with a single rooster then 2 roosters in with the remaining, larger flock of hens. I generally have a few roosters that will remain free ranging to swap in and out of the pens later on. I like keeping the roosters happy as the hens.
With a good plan to keep them happy and healthy, I have not seen a need for heat other than for my tiny Serama's and any chicks that will need it till spring.
I know this thread was about what type of heat do we use but my answer, in a nutshell, is the best health possible and a draft free place to roost.
So relieved
