silkies arent the most cold hardy of chickens, i would recommend heat lamps for them - red lamps.
the big issues with using light for heat (we do it here), is over stimulation - and if you only run one lamp and it blows, they get chilled.
if you run white lamps 24-7 the chickens become over stimulated, laying very well for the cold temperatures; and using alot more feed. when you turn the lamps off, it forces a molt that kills your egg production. when i turned my lights off last summer i went from about 8 dozen eggs a day out of that barn, to maybe a dozen (a day) in less than a week. red lamps seem to help as the chickens will sleep under red light, consuming less feed and not laying as much. make sure they can get away from the lamp, if you put your hand under a red lamp for a few seconds you wont feel much heat. if you leave it there you will get a burn in a matter of minutes.
to avoid the lamp blowing and the chickens getting chilled, use 2 lamps on opposite corners of the coop. that way if one blows there will be a backup. now for the other down side - be prepared for a power outage with either propane heat, or a generator.
if you can "lower the roof" of the pen it helps too, i have some 8x8 pens with a peak at 3 feet. on these pens if i block the wind on 3 sides and keep plenty of bedding in, i never have comb freeze.
as big medicine mentioned, make sure you have a draft- and feed some cracked corn late in the evenings on these cold nights. the corn probably works better than lamps for most breeds.
bantam breeds, light weight breeds, and breeds with large straight combs are less cold tolerant than others. if you have a pen of buckeyes or brahmas, corn would probably be all you need- as long as they can get out of the wind.
I've added myself.
