Just a general caution if you use lamps be careful. I had a heat lamp in my coop way up in the top of it in the corner, way out of the way, it was a light bulb type. Well, chickens can be retarded sometimes. She was jumping up to get on the perch, one of the others did not like it, they somehow squabbled a jump off of sorts occurred, and mid hop, wings flapped, and somehow this bulb way up in the corner got broke. I was there when it happened or i'd never have known how they managed that. Glass everywhere from the broken bulb. Luckily this happened when it was NOT turned on. If it was on, it could have been a big problem. Glass shards to cut them, electricity from the hanging filament, fire??? No telling. Not to mention the base of the bulb with very sharp shards of glass still hanging on it. If they decided to continue quarreling and hit that thing again that would have sliced someone clean open. And YES the bulb was caged. They knocked the whole thing hard enough to break the bulb and knock the cage off the bulb.
Heat rocks like you use for lizards might work too, the heat comes up through the straw and up into the coop for them. If they poop on it, it washes right off, just like it does when your lizard poops on the rock. A convection heater can work in a pinch,blow warm air in there, I hung the heater OUTSIDE the coop, blowing into the window. set it to 500 watts, worked nicely. Kept them warm but not overly hot. The wind was howling that night so I was worried the air would cool them too much, so did that for extra heat, otherwise I dont bother, it rarely gets cold enough in Florida to worry.
Aaron