@Roada Red, it seems counter-intuitive that ventilation is better in cold weather than auxiliary heat at preventing frostbite, but it's pretty well been proven many times by many people.
Yep, unless you devote to going all out to heating and maintaining the coop above freezing at all times with a 'proper' up to code heating (not extension cords or heat lamps) while still balancing the ventilation that is still necessary to rid the coop of ammonia gasses then it's best to avoid heat totally as the cons outweigh the pros in almost all instances unless fully devoted and done correctly...
As many know I'm not against heating if done properly, as I heat my own coop to about 35°-40°F all winter, but it's done with a forced air furnace just like you have in most houses, that furnace has multiple levels of additional filtration that are checked every day and the furnace is cleaned weekly of anything that gets past the filters... My coops size at 1800 sq/ft is much larger than most, and even so I continue to vent it even while heating, I just dampen down the venting day and night and based on outside temps... It's a lot of work and requires near daily adjustments, hardly some plug and play setup...
I would never just toss a heat lamp in the coop and call it a day, that is dangerous and likely to cause more issues then it begins to solve...
If you are going to 'heat' a coop for cold intolerant breeds I suggest a heat box inside the coop using a radiant ceramic heater similar to this setup, this will trap some warm air around the bird, but sill allow normal ventilation in the coop and if sized properly the birds head is in the constant fresh air from ventilation and the exhaled air is also exhausted... The red being a radiant heater, spaced off the back wall with a screen in front of it to stop the bird from leaning against it... These ceramic heaters never reach combustion temps so the risk of first is extremely low...
Also one has to really consider the temp, I know for warm weather people anything bellow 32°F seems cold but honestly it's not and for most chickens it's not even a mild concern at any above 0°F as long as there is proper ventilation to rid the coop of excess humidity...