equibling, so sorry about your birds! That sounds really cold to me down here in TN. I have experimented with three different heat methods in my three (small) coops. I have a relatively small flock (12 birds, mostly bantam) spread among 2 primary coops and one portable. Here's what I have tried:
1) reptile heat pads sandwiched on ceramic tiles (portable mini coop, 4' x 30", 2' high interior) ~ maintains 10-12 degrees above external temp
2) ceramic heat lamps (small/med coop, 5 x 4, 3' high interior) ~ maintains 20 degrees + above external temp
3) mini sealed oil-filled heater (largest coop, 8 x 6, 6' high interior) ~ seems to maintain 12-15 degrees above external temp, but the new, larger heater will probably add 10+ degrees to this.
Coop #1 has one 12" tile from Shopthecoop.com, and one mini tile we made ourselves.
For Coop #2, here's the info on the ceramic bulbs ~ I believe Shopthecoop also sells these ~
http://theworldofjenotopia.com/cmsjoomla/index.php?option=com_content&task=view&id=53&Itemid=27
For Coop #3, the largest coop, we made a "table" that raises the heater 2' from the floor. It is bolted to the wall for stability, and is completely caged (to the ceiling) in 1/2" hardware cloth so no one can get near it.
I have not yet added all this info to my website. Feel free to PM me for details or more info. I feel quite safe with all my options so far, but I check the condition of things every day and I keep the lamps wiped down so dust does not accumulate.
I just bought a length of reptile heat rope and a thermostat, and I will keep the forum posted on how this works for a small coop.
Good luck!
Ed. to add ~ INSULATION is probably the most important part of coop planning I have found. The last coop we did, we made in three layers, with foil-backed foam insulation. Makes a huge difference, and keeps things warm and dry inside. If I had it all to do over again, I'd insulate every coop. In fact, I have gone back and retro-fitted parts of all of them (esp. ceilings).