We’re in Vt, probably not Mt cold but close. I’m new to the discussion here but not to wintering chickens. We do use a heated waterer outside the coop. We also use lights (not heat lamps, but CFL or LED inside plastic trouble lamps) to provide about 14 hrs total light on average (daylight + artificial) so a couple hours at each end of the day. This helps keep egg production going, and it also adds just a touch of warmth.
On those minus 25F wind chill days (you know the ones) the chicks do stay inside, and if it continues overnight I might leave the lights on. I’ll also place a feeder and heated water bowl in the coop. The top vent is always open but wind-proofed. Other winter days (above zero) the small coop door is open and they‘ll venture out, even into a foot of snow (though I’ll shovel a path to the food and water).
We‘ve never used a heater or heat lamp, and learned the importance of cold-weather ventilation early on when some hens got frost-bitten combs from high indoor humidity / ammonia levels.
Hope this helps. Stay warm!