I am in the mountains of N E Georgia lowest temps aro here mostly in the low teens lowest around 8 or 20 sometimes snow, hens love it their coop has a wide open front. Never could understand insulating or heating your coop. Summer is the time to think of helping your hens. Shade or even a fan. Just my opinion. Coons and opossums are what gives me a restless sleep not the weather.What kind of and how much ventilation do you have?
What breed is the little rooster?
We get well below zero here. Even in a solid week of the high being a whopping 3°F with lows at -16°F no frostbite even on the leghorn hens.
Good ventilation will let the moist air rise and exit the coop. It is very important to have good ventilation.
That ventilation will make adding heat moot as that heat will be rolling out the vents not staying in.