Mike they'll be fine. I brooded in the garage and there were some cooler days. On extra cooler nights I partially covered the wire top of the brooder with a bath towel to help hold in heat. And of course left an opening with safe margins for the brooder light to warm. How many weeks are the chicks? They might have enough feathers to help with keeping warm as well. Once the body is feathered they're doing quite a bit on their own to keep warm.