We don't use any but our climate is pretty mild here. Our chicken houses face the south and have large windows on the front, on sunny days the house get nice and warm during the day, at night we have quite a few birds so they put off a good bit of heat themselves.
Like others have said a good house is the key. Since you only have a few birds I remember somebody saying last year that they closed off part of their chicken house. With a smaller space the birds were able to warm it themselves.
Age has alot to do with winter laying and length of the day. Our older birds pretty much quit Dec/Jan and pick up again as the days get longer. We try to have some just start laying around Oct/Nov and they will lay thru the winter, the day length doesn't seem to bother them.
Steve in NC