We've gotten 24, 23, 23 and 22 eggs for the past four days from our 29 GC's. They've been working hard in all this bitter cold here in Central NC so far. I think it helped that we put back up our tarps on the north, east, and west sides of the run so it forms a windbreak for them. We left the south side open so they can get the sun all day when it's out. Last night it got down to 12F but when I opened the coop doors at 7:00 it was a balmy 38.5F inside. One thing I've been doing is to fill their big plastic waterer with very hot water and sitting it inside the coop with them before I close them up for the night and I take it out in the morning. The coop is 4d'x8w'x4h' and I've been sitting it over in the corner away from the roosting bars so they don't make a mess on it. I think it's been helping on these bitterly cold nights. It's more than 100' from the nearest outlet so I can't very well run a cord down and put in a heat lamp so this is what I think is a good solution to the problem.