Hello! It has never been this cold here, that I can remember! This our second winter with a flock, and we only have 3 girls in our coop. The coop is relatively small ( see photos). I would like to put in a heat lamp, but am afraid it may get too warm. Should I put in a heat lamp or just a 100 watt bulb? It is currently -5 degree but tonight and tomorrow we will hit double -17. Any advice would be greatly appreciated!