yawninggreyhound - my layer coop is from the same person. First thing we did was add insulation and inner walls in including a ceiling. The insulation we used was that stuff you buy in a roll that looks like foil around bubble wrap. If I put enough birds in there it raises the temp over outdoors by maybe 10 degrees. If your birds are draft-free they will be fine. If you want to supplement heat safely look for a ceramic heat emitter in the reptile section at the pet store, but now that we are past the sub-zero nights I would not worry. If we have another cold snap it won't hurt to prepare, but as I said a couple of days ago, if I didn't have chicks out in the coop I would not have supplied any extra heat. This is the first time I have done so, it is a minimal amount of heat in place only to ensure ambient temp in the coop stays above zero, which is about all it's done. Chickens are tougher than you think they are 
