Hi, 
I am not an expert as I have only just started in September, and to be honest I did not expect to get any eggs until next year, as my chickens were quite young and I really could not afford or engineer lights in the coup, as I am currently off work with severe arthritis, so I just muddled along bonding with my girls who I love dearly, eggs or no eggs, and BINGO!!!
To my amazement, 2 of them are laying, and now at this coldest time here. 
I had bought Black Rocks as they are supposed to be hardy, but I was not hopeful.  But they have exceeded all expectations. So completely without any artificial light or heat, they are producing 2 eggs a day ( and I only have 4 chickens) a third is now looking very much like she is due to start, her comb is well pronounced and she is huddling down if we approach her and this has been the main sign with the others too, and slowly the final girl Becca is coming along the same path. 
The temp here for the past few days has been -5 degrees C, so I think they are doing ok, it is too cold for me...lol. 
I don;t know if I am just lucky, but I am so very proud of my girls...lol. 
Hope you have the same kind of luck, 
Jena.