I live in Colorado, in a place where in my coat in my brother's car, I am literally shaking. There is usually some snow on the ground in the winter, not a lot of wind, and usually just very cold air. The coop and chicks have not arrived yet (I'm actually building the coop.) They will probably get here around August 20th, and as for the coop, I was going to do a simple 24 square foot A - frame for 6 chickens. It will be able to be completely shut off from the run, which is pretty big, and is half covered. There is a 0% possibility I can get heat in the coop, but there will be lots of nice straw and I can put up cardboard around the walls (plywood.) At what age would chickens (cochin, wyandotte, andalusian, and EE) be able to move to the flock as a group? I was initially thinking late October/early November, but at that time, usually I'm in a hoodie every day! I'd be concerned that a 5ish week old flock raised in my garage and house would freeze. The time I can keep them in the house is very limited, as my HOA has little tolerance for chickens being on my lot (the chicks are moving just down the street to a farm where they are allowed). Is putting them out at 6 weeks okay?
Fully feathered is the rule of when they can safely go to the coop - usually about 6 weeks so you'll be fine and so will they! Chickens handle cold better than hot weather. Heat in the coop is not necessary as long as you have a draft-free (but ventilated) coop. Here is an article that addresses cold weather and chickens! https://www.backyardchickens.com/newsearch?search=so+you+think+it's+too+cold
We didn't put ours out until the weather was 40 degrees at night and they were pretty well feathered. Do you have a deep cycle marine battery? You could rig a 40 or 60 watt incandescent light bulb to the battery to knock the chill of of the roost area at night and then charge it back during the day. The bigger the birds are before you put them in the cold the better. Another though might be to make the inside of the coop by walling it off with something with a high R rating so they they not only stay close together to share body heat but it gets reflected back into the coop instead of lost with the insulation.