Sounds like a molt to me, too. I have one currently in the same state. It is ridiculously cold where I'm at and the hens that are molting have been spending a lot of time inside the coop during the day, which is unusual for them. The cold does seem to be bothering them a bit more than usual. I would not add any heat unless you are really worried. Chickens are really tough and can handle just about anything that is thrown at them. Supplemental heat may give you more problems in the long run than you anticipate. If your birds are acclimated to the cold they should do fine, but if they are used to toasty warm temps and the power should go out, you will have some pretty miserable birds.
Good luck.