Unless we have another bitterly cold winter like last year don't add heat. I would say don't at all unless you start having issues with your birds. If they get used to having heat and aren't acclimated to the cold....if your power goes out you could lose your whole flock. I only put heat a few feet above them if it was below zero at night last year. They got sent to bed with a warm meal in their bellies and they huddle together. Our lowest nights were almost -30. The only two who had it rough were my leghorn and a huge combed mixed roo. The leghorn molted also, which didn't help her.
If your birds are feathered in, don't mess with them.
Tough little things that need less help than we give them credit for. I also had broodies with fresh babies when it was only 20' as a high outside. The babies grow and feather out faster outside under mama. Air circulation, dry, nice roosts...easy.
They are really flighty when they are babies. They are 5 weeks old on Monday and will be going outside soon. They are just now starting to wonder who I am. They are very curious chickens but also very leery of new things,
As if they have retained some of their "Wild" instincts. I am putting pictures so that you can see the little Puff of feathers on the top of their heads.
They looked different as chicks but now they are so close in color that I can barely tell them apart. They are right in that weird ugly phase. 
I so love my Chickens I did not realize that I would become so attached. I bought three different batches and the first batch has two White leghorns that just started laying last week at just over 15 weeks which I think is really early, but Who am I? I am no expert.
So included in all three batches are; 2 white leghorns, 3 Easter Eggers, I buff orpinton, 1 Cockoo Maran, I Barred Plymouth Rock, 3 Blue Favaucana, 2 Delawares, 2Cream Legbars and 1 Jersey Giant. I plan to see which breeds I like the most and then get more of those next summer. 
So far the Blue Favaucanas are the friendliest :cd Sorry I didn't mean to ramble on. So I got them at my Pet Chicken and they were 49 dollars a piece. 
