I'm a firm believer in keeping chickens out of severe cold. They were tropical birds after all! I hesitate in saying "keeping them warm" all winter,, because that isn't practical. I don't want an extreme difference in the outside temps and the coop. I just don't want it "freezing" inside the coop. It gets cold in Kansas. But NOT below zero. My current coop is big (10x10 + 8' ceiling). It is insulated but the windows are inferior. I keep one of those oil filled radiator-look heaters in there. I used to have one of those big heat bulbs but never again. It fell one day and started burning a hole in the floor. Why the whole coop didn't start on fire is beyond me. Scarey. Anyways, the heater works well since there are no open flames and they won't get on it. I think a tiny coop like yours may be heated enough by a 100 watt lightbulb, properly caged and protected.