That happened to me two winters ago with my 8 hens, the heat lamp bulb just popped around 2am and it was 9 below outside. I ended up grabbing every old blanket and towel in the house and draping them over the coop like a tent, then shoved hand warmers inside their nesting boxes wrapped in socks so nobody got burned. The hens actually huddled together on their own and were fine, turns out they handle cold way better than we think as long as they stay dry and out of the wind. What saved me the next day was hitting the farm store for a backup bulb plus a cheap thermometer so I could actually watch the temp instead of guessing. Now I keep two spare bulbs and a roll of that reflective bubble wrap stuff in the shed all winter, cost me like 15 bucks total and I have never had a repeat of that night. The garage thing works in a pinch but man does it get messy fast, mine pooped all over my husband's work bench and he still brings it up.