One of the best things you can invest in when getting backyard chickens: a remote temperature reader. This way, you can obsess over the slightest temperature variations and neurotically check on your ladies to make sure they’re not chickensicles. (They’re not- in fact, they’re fine down to around 0degrees without any heat source, so long as they’re dry and away from drafts.)
Ferndale Chickens 
Ha! “Obsess over the slightest temperature variations” – that would be me if we set our remote thermometer up in the coop! As it is, we finally broke down and set up a 60W bulb in the coop today. It is just WAY too cold out there today, even for my feathered friends.