We live in Iowa where it averages 80-90 degrees in the summer and they have been allowed to free range during the day. (8am to 8pm) with no restriction. We noticed in the morning they are dying to get out of the coop. However what should we expect in the winter? We average 5-15 degrees with snow? Will they be ok being locked up in the coop? Or should we still let them out? We plan to get some heating for the coop floor but if we leave the door open then it will be hard to heat..
I always leave a little chicken-sized door open. I live in MI and my coop is not heated at all. Your chickens would be okay locked in the coop, but if they're willing to romp around in the snow I wouldn't stop them (just be a little wary of frost bite.) Personally, my chickens won't touch the snow if it is deeper than an inch. I hope I answered your question!
Chickens do fine in colder weather as they have a thick feather coat keeping them warm. Heating the coop overnight if the temperatures drops really low may be a good option for you, but usually a cozy, dry insulated coop that is draught free is adequate. Here is a discussion on chickens and cold tolerance that may interest you: https://www.backyardchickens.com/t/421122/think-its-too-cold-for-your-chickens-think-again
I always leave the pop door open and give them the option. They often don’t venture out in snow for a while, (chickens don’t like change) but once one gets brave and ventures out, many will. Don’t worry about frostbite as long as they have proper ventilation in the coop and a direct breeze is not hitting them when they are sleeping in the roost. When given the opportunity, mine walk around outside in zero degrees Fahrenheit weather. They walk on ice and snow. They don’t like a cold wind hitting them but just cold temperatures are not a big problem.
Your chickens will still want to go out. They might not like the snow so shovel part of their run so they can still scratch and roll around in the dirt. Mine love to sunbathe in the winter so I fashion a sunroom for them with old sliding glass door. I wouldn't run any heater in the coop for adult birds. Not worth the risk of fire. My chickens do fine in freezing temps. Go with a light if you need to and add extra straw and shavings on the floor to provide more insulation.