Hi everyone. New member here, reader since we got our first chickens last spring and I'm having some issues with some of my girls getting frost bite on their combs and I've been doing a ton of research but I'm still not sure what to do. I'll detail our setup and I'd love some advice if anyone cares to share any. We've got a rather small coop for our 20 chickens (expansion to come, we started with 6 pullets and raised 14 chicks from day-old for my dad, who then wanted them to stay with me, so they moved from a mobile coop into the big house with the older ladies just in time to start laying) so we struggle a bit with moisture but use a droppings board and a couple of high vents to help with that. It's a raised coop, double walled construction 2x3 framed and OSB chipboard interior and exterior, but not insulated. We have a covered run with two of three sides tarped (so only one large side with the man-door untarped) and plastic sheeting covering the three sides of the under-coop portion to cut down on snow and wind in the run and heat loss under the coop. The run is sand covered by hay which we freshen every week or two and the girls love to snuggle into. The girls love their run and being outside no matter the weather and have some big branches mounted from the roof that they snuggle up on. They don't care to leave the run since there's been any snow on the ground and other than a couple of days where there was grass visible on our yards paths, and they were frolicking, I don't expect they'll want to come out much until the thaw (we've currently got a couple of feet of snow in most spots). We've got a cookie tin water heater that works in all but the coldest weather that we switched to when the heated nipple waterer started freezing and leaking water all over. Bedding in the coop is shavings, usually changed about weekly depending on how much time the girls have been inside mucking it up. So my dilemma is some of the girls are showing signs of frostbite on their combs (even the small combed breeds) and we're in a cold snap of -35C (-45C windchill, -31F, -49F windchill) and that's too dang cold. Some have the pale discolourations and others have purplish discolourations and swelling. The coop keeps them protected from the wind but it isn't much warmer than the outside temps, maybe a couple of degrees, if that. So we caved and put a heater in there. And this is what I'm losing sleep over. Hubs installed a shelf, he put up chicken wire so the girls can't get on it or near it, he put it on low and set the thermostat to low (it's a little box style heater, the kind I've used under my desk at an office job, we didn't want to do a heat lamp because of the horror stories we've heard nor were we set up for one, the fixtures are still attached to the brooder in storage buried in a shed), and he installed a smoke alarm. The coop is about 25ft from my bedroom and I'm sleeping with one ear open and working from my bedroom, not to mention the window open just a hair in case the smoke alarm goes off. And the heater is also on a remote so we can turn the power to the plug on and off from inside the house if we wanted to. I'm paranoid, can you tell? Everything I've read says don't heat your coop, they don't need it, they'll adapt, but then I read that these people writing these things are talking about temps that sound like they're barely below freezing (I'm not very familiar with fahrenheit but 20F, which is one of the coldest I've read, is not that cold to a Canadian, that's collect the eggs and check on the girls in a nighty weather). And it's clear to me that it must be too cold right now because even when we vent the coop all day to dry it out, they're still getting signs of frostbite. So anyway we've been heating the coop since Friday evening (it's Sunday morning now), keeping it around -15C (5F) which the chickens seem very happy with and we kept them inside most of the day Saturday letting them outside only to eat and for the first time ever most of them finished eating and high tailed it back inside right away so we're doing so again today and we even moved their feeder inside so they don't have to go out at all today. After today the temp is supposed to go back up to -5C (23F) for a couple days and then back down to -20C (-4F) and then back up so I'm planning to take out the heater and clean it and the filter in between cold snaps (we only plan to use the heater in extreme cold) to reduce the risk of fire, but I'm still so dang nervous. The horror stories of coop fires have me freaked out but I can't have all my girls suffering half of their combs falling off because I can't figure this out. I'm also worried about the damage the girls have already suffered. They don't seem to have any issues on their feet or waddles, just their poor discoloured and somewhat swollen combs. I'm hoping that keeping them locked up for 2 days will help them start to heal but after that I have no idea what to do. There are too many showing frostbite for me to set up an infirmary in my house for them. So any advice on the heating or the frostbite would be very much appreciated.