Hello there and welcome to BYC!
Chickens can tolerate some very cold temps, even temps below zero. It is never recommended to add heat to your coop unless you have very young, old or sick birds. They are designed with lots of feathers and down to keep them warm. However if it is going to get down to -15 or -20, you might add a small heat lamp to the roosting area just to bring up the temp a bit. My rule of thumb is, if it is going to get 30 degrees colder than the average over night low, then I will add heat at night only and then remove it when temps return to their normal over night lows. If you do use a heat lamp, permanently attach it to a wall or ceiling so it cannot fall down in the night and start a fire. No extension cords laying on bedding or anything like this.
Good ventilation is EXTREMELY important to preventing frost bite. You will want about 3/4 to 1 square foot of vent space in your eaves per bird at all times. All the breathing and pooping moisture has to go somewhere. Without proper ventilation, it is going to rise and then fall back down on your birds as water or frost. Birds can withstand the coldest of temps if the air is dry. Use ventilation high above their heads, vents on opposing sides of your coop eaves...preferably one side of vents higher than the other to create a nice air flow in the lower side and out the upper side. Your birds roosting low to the floor. The moisture will rise into this positive air movement and get whisked away. If it is going to be really windy that night, you can block off 2/3rd of the lower venting to prevent the heat from being sucked away from the birds. And use a 2x4 for a roost bar, the 4 side up so they can cover their feet and toes with their breast feathers to prevent frost bitten toes. You can also use vaseline on combs if you start to see frost bite. Never close up your coop tightly. This will create bad air space and can cause all kinds of respiratory issues. Always keep that air moving!
You can wrap an old towel around your roost bar. This will help to keep the feet warm. Birds loose heat through their feet. So warm feet mean warmer birds. I wrap mine sometime early December. I also cover my windows with clear plastic. That way I can open the windows in the coop but keep the winter winds from blowing in.
Your birds should have the same outdoor time as they normally do in warmer temps or at least the opportunity to get outside. You can shovel the snow out of the way for them to get out and scratch around, but don't let them stand for long periods on snow as they can get frost bite on the feet. Provide places they can hop up off the snow.
I use heated dog water bowls or heated water bases. It gets to be too much to haul water around every other hour when it is below freezing outside.
Good luck this winter and stay warm! :-)