When God created Adam, he charged him with a mission. He was to take dominion over the birds in the air, the animals upon the ground, and the land itself. (Gen. 1:26) Sometimes it feels that those things didn't get the message that we are to have dominion over them. For example, we tried to grow some broilers over the winter, because I AM MAN! That turned out to be a horrible failure. So we waited until the weather got warmer, in February mind you, and tried again. The first week of their little lives, we had a huge snow storm, we actually had snow on the ground when they came in the mail. But they survived the week and I started to think I actually knew what I was doing. Then during their second week of life, I realized that I in fact did not know what I was doing and the chickens started dying in bunches. Birds tend to pile up and crush the ones underneath the pile. It's like a chicken version of king of the mountain, only instead of a hill of dirt, they get on top of one another until they form a pile of chickens. It's really sad when you come out in the morning and there is a pile of them crushed down. Usually at that time it's warm enough that the survivors are just milling around like nothing happened.
A fellow farmer once told me, "Once they start piling up, ain't nothing you can do to stop 'em." Now I just assumed he was exaggerating - he was not. I put waterers and cans and various objects and they would just pile as close to that original spot as they could. It's like they just wanted some warmth, just for a moment until the weight of their brothers slowly crush them. As I have stated before, I don't really know what I'm doing. So I started reading about hovers and I built one out of an old, slightly broken plastic crate.
Here is the basic approach. The chickens need about 90 degree ambient temp or they get too cold and die. One of the hardest things to do is to heat up a room to 90 degrees, especially when the outside air temp is in the low 30s. So when it gets too cold they huddle, wouldn't you? They also tend to dig into the bedding a little which will make a slight depression. More chickens want to get into the middle where it is warmer so they keep jumping into the middle and piling on top of one another. The little guys in the middle get warm, but usually get crushed as an end result. The hover does two things: it reduces the amount of air you have to heat up and it allows the chickens to move in and out of the warming area. I used a large plastic crate and cut holes in the side for the heat lamps. I turned it upside down and set it on bricks. This allows the heat lamps to heat up the air inside the crate, and since it is upside down the heat is trapped in the crate. It's up on bricks so the chickens can come and go - in and out of the crate without piling.
Here are a couple of pictures to help you see what we're doing. The first picture is in the daylight, so not many are under the crate. The second one is at night, so they are almost all under there. The last one is a bird's eye view.