-13 degrees in the Colorado mountains

I personally would never heat the coop. You probably have your fair share of power outages up there and I would rather have them acclimated to the temps. Heat lamps are also a fire hazard.\ with all the dust and bedding in a coop. Bed the floor with a thick layer of straw or shavings, keep them dry and out of a draft and they will be fine.

I don't change their feed in the winter other than add roasted soybeans when they are molting which they are right now. Mine also double their feed intake in the bitter cold.

 

First off, what breeds are your chickens? How old are they? Breed and age are big factors in the Winter.

When thinking about the weather and chickens the first thing you should do is go outside and put your fingers inside of your chickens feathers (like a little oven)!!!! Depending on breed they may not even need the heat.

If you are going to leave heat on for them that is fine, as long as you are aware of fire hazard and so on. I would turn off the heat durning the day and on more mild nights to keep them acclimated to the weather.

As far as feed, as Percheron said, they will increase their intake by a LOT. I breed, and I always bring my numbers way down in the winter. So make sure they have plenty to eat so that they can produce enough energy to stay warm. A snack right before bed will go a long way to help keep them warm through the night. Also make sure they stay busy and active. I throw out treats and hang up fruit and vegtables to give them stuff to peck and scratch at.

 

You have one heat lamp too many. You don't need a thermometer in the their house, and you're probably right about them being too hot. Chickens have their own wonderful, insulated heating system. It's their feathers. They acclimate to the cold by growing more downy feathers, just like your dog, cat, horses and cows grow thicker hair in the winter. The most important thing about housing chickens in the winter is keeping their coop well-ventilated to keep the humidity down. Yep, you want a little air-flow, even when it's this cold. I'm in MN and have been keeping chickens for over 25 years in sub-zero temps and have never had one freeze to death. Too much humidity will cause frostbitten combs and wattles and make your chickens feel more chilled. You know those cold, humid days - the soak into your bones kind of cold. Too much heat in the coop causes humidity to build because it keeps the manure and urine thawed and that moisture gets in the air. They're much better off with deep, fresh bedding. Another thing to consider. When you go outside and bundle up with coat, snow pants, boots, gloves, etc. you can take it off when you come back in. Try leaving it on for a while when you get back in and see how uncomfortably hot you get. Your chickens don't get to take off their down coats. A somewhat consistent temp is much healthier for them.

Some people will feed a higher-energy feed. Something with more fat in it.