Whether you choose to add supplemental heat to your coop or not is entirely up to you. You can google things like Sweeter Heaters, various flat paneled heaters, thermocubes (temp. range controllers for plug in devices such as fans/heaters), etc. Animals (including dogs and cats) can live through conditions that are far more harsh than you or I could stand. Since I view my chickens similarly to my dogs and cats (in the pet category), I do try to make mine more comfortable w/a little supplemental heat on the coldest of nights (which we won't hit until Dec./Jan).
But do know that if your coop is draft free (but leave some ventilation open) and has plenty of bedding, chickens can survive in temps. down below zero.
But do know that if your coop is draft free (but leave some ventilation open) and has plenty of bedding, chickens can survive in temps. down below zero.