Popsicle is right--temperature doesn't have much to do with hens laying in the winter. They need supplementary light--usually a regular 75 watt light bulb on a timer to come on at 4am and go off around sunrise will do it. Also, hens should have free access to a balanced layer ration, instead of being limited to twice a day. Feed limiting is actually a technique used to force a moult in commercial layer houses.
If you give your hens a lot of scraps, you may be messing up their nutrition, as well. Remember, a hen has a tiny body weight so anything you give her will count quite a bit in her daily nutrients. I don't have a specific example for hens, but when I had a parrot, my avian vet told me that ONE GRAPE would change his nutrition for the whole day since his body weight was so small. So pay attention to what scraps you're giving, and try not to give too much sugar or fat. You might also want to put out a free-choice feeder of oyster shell or crushed egg shell if you feed a lot of scraps.