lilshadow, I live in MN too and it got to -12 here last night. This morning all the hens are fine and healthy. And I'm expecting 10 to 13 eggs from these 16 hens today.
Supplemental heat is not needed. Just good ventilation and elimination of drafts. Giving un-necessary heat just lowers natural hardiness. Keep em tough and strong I say.
For winter egg production we use 2 timers with a 40 watt bulb, plus a 7.5 watt bulb for dimming. Both morning and evening hours are extended for a daily total of only 12 hours.
Giving additional light both in morning and evening means you can set the timers in the Fall and never have to adjust after that.
Good luck,
spot