I am in the "no heat" camp but I have to say, you aren't doing them any favors having heat on them at 10 weeks of age. They should have been weaned off the heat weeks ago. I've never had heat on them beyond 4 weeks and by 6 weeks they are fully feathered and definitely don't need it. By offering heat now, you are delaying their acclimatization to cooler temperatures, making it harder for them to transition.
Reasons not to offer heat:
* They don't need it! Birds grow a downy undercoat that keeps them warm. Wild birds don't have heat and survive winters just fine.
* Coop fires. Stick around the forum and you WILL read about several coop fires among our very own members this winter, almost always started by someone trying to provide heat to their coop.
* Power outages. Once the birds are reliant on heat, what happens when you have a power outage and they don't have it for a day or two? They suffer worse than if they'd never had it in the first place.
I'm sure there are others - those are just the ones that immediately spring to mind.
I'm not in Wisconsin but where I live it does occasionally get down to the single digits. I won't say they're happy at those temps, but they survive them.
I don't insulate either. What birds need MOST is good ventilation. Ammonia build-up from a poorly ventilated coop is far worse for them than cold temperatures. It is almost impossible to provide good ventilation AND insulation.
The best set-up is a coop that has good ventilation while not being drafty. The best way to think about it is: a draft is air flow that is blowing directly over the birds. Ventilation is allowing for good air exchange. So, ideally, your ventilation will be at a level higher than the birds are roosting, so that stale air can move out and be replaced by fresh air, while not blowing directly ON the birds.
